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  • Periodicals Archive Online (PAO)
  • Annual Reviews
  • 1995-1999  (979)
  • 1980-1984
  • 1999  (979)
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  • 1995-1999  (979)
  • 1980-1984
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  • 1
    Electronic Resource
    Electronic Resource
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 117-142 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract The enteric nervous system exerts local control over mixing and propulsive movements in the small intestine. When digestion is in progress, intrinsic primary afferent neurons (IPANs) are activated by the contents of the intestine. The IPANs that have been physiologically characterized are in the intrinsic myenteric ganglia. They are numerous, about 650/mm length of small intestine in the guinea pig, and communicate with each other through slow excitatory transmission to form self-reinforcing assemblies. High proportions of these neurons respond to chemicals in the lumen or to tension in the muscle; physiological stimuli activate assemblies of hundreds or thousands of IPANs. The IPANs make direct connections with muscle motor neurons and with ascending and descending interneurons. The circular muscle contracts as an annulus, about 2-3 mm in minimum oral-to-anal extent in the guinea pig small intestine. The smooth muscle cells form an electrical syncytium that is innervated by about 300 excitatory and 400 inhibitory motor neurons per mm length. The intrinsic nerve circuits that control mixing and propulsion in the small intestine are now known, but it remains to be determined how they are programmed to generate the motility patterns that are observed.
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  • 2
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    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 283-310 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Intercellular channels present in gap junctions allow cells to share small molecules and thus coordinate a wide range of behaviors. Remarkably, although junctions provide similar functions in all multicellular organisms, vertebrates and invertebrates use unrelated gene families to encode these channels. The recent identification of the invertebrate innexin family opens up powerful genetic systems to studies of intercellular communication. At the same time, new information on the physiological roles of vertebrate connexins has emerged from genetic studies. Mutations in connexin genes underlie a variety of human diseases, including deafness, demyelinating neuropathies, and lens cataracts. In addition, gene targeting of connexins in mice has provided new insights into connexin function and the significance of connexin diversity.
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  • 3
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    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 337-362 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract ATP-sensitive K+ channels (KATP channels) play important roles in many cellular functions by coupling cell metabolism to electrical activity. By cloning members of the novel inwardly rectifying K+ channel subfamily Kir6.0 (Kir6.1 and Kir6.2) and the receptors for sulfonylureas (SUR1 and SUR2), researchers have clarified the molecular structure of KATP channels. KATP channels comprise two subunits: a Kir6.0 subfamily subunit, which is a member of the inwardly rectifying K+ channel family; and a SUR subunit, which is a member of the ATP-binding cassette (ABC) protein superfamily. KATP channels are the first example of a heteromultimeric complex assembled with a K+ channel and a receptor that are structurally unrelated to each other. Since 1995, molecular biological and molecular genetic studies of KATP channels have provided insights into the structure-function relationships, molecular regulation, and pathophysiological roles of KATP channels.
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  • 4
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    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 391-415 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract In this article, we review the basic pharmacological and biochemical features of endothelin and the pathophysiological roles of endothelin in cardiovascular diseases. Development of receptor antagonists has accelerated the pace of investigations into the pathophysiological roles of endogenous endothelin-1 in various diseases, e.g. chronic heart failure, renal diseases, hypertension, cerebral vasospasm, and pulmonary hypertension. In chronic heart failure, the expression of endothelin-1 and its receptors in cardiomyocytes is increased, and treatment with an endothelin receptor antagonist improves survival and cardiac function. Endothelin receptor antagonists also improve other cardiovascular diseases. These results suggest that the interference with endothelin pathway either by receptor blockade or by inhibition of endothelin converting enzyme may provide novel therapeutic drugs strategies for multiple disease states.
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  • 5
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    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 417-433 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract The acquisition of a sexually dimorphic phenotype is a critical event in mammalian development. Although the maturation of sexual function and reproduction occurs after birth, essentially all of the critical developmental steps take place during embryogenesis. Temporally, these steps can be divided into two different phases: sex determination, the initial event that determines whether the gonads will develop as testes or ovaries; and sexual differentiation, the subsequent events that ultimately produce either the male or the female sexual phenotype. A basic tenet of sexual development in mammals is that genetic sex-determined by the presence or absence of the Y chromosome-directs the embryonic gonads to differentiate into either testes or ovaries. Thereafter, hormones produced by the testes direct the developmental program leading to male sexual differentiation. In the absence of testicular hormones, the pathway of sexual differentiation is female. This chapter reviews the anatomic and cellular changes that constitute sexual differentiation and discusses SRY and other genes, including SF-1, WT1, DAX-1, and SOX9, that play key developmental roles in this process. Dose-dependent interactions among these genes are critical for sex determination and differentiation.
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  • 6
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    Palo Alto, Calif. : Annual Reviews
    Annual Review of Physiology 61 (1999), S. 683-697 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Vasopressin or AVP regulates water reabsorption by the kidney inner medullary collecting duct (IMCD) through the insertion and removal of aquaporin (AQP) 2 water channels into the IMCD apical membrane. AVP-elicited trafficking of AQP2 with the apical membrane occurs via a specialized population of vesicles that resemble synaptic vesicles in neurons. AQP2 vesicles and the IMCD apical membrane contain homologs of vesicle-targeting and signal transduction proteins found in neurons. Expression studies of AQP2, including human AQP2 mutants, suggest that the carboxyl-terminal domain of AQP2 is important in AQP2 trafficking, particularly as a site for cAMP-dependent protein kinase phosphorylation. These present data reveal that IMCD cells possess a complex integrated-signaling and vesicle-trafficking machinery that provides integration of AVP-elicited water transport with many other parameters within the IMCD cell as well as kidney.
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  • 7
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    Annual Review of Anthropology 28 (1999), S. 509-529 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Human beings are biologically adapted for culture in ways that other primates are not, as evidenced most clearly by the fact that only human cultural traditions accumulate modifications over historical time (the ratchet effect). The key adaptation is one that enables individuals to understand other individuals as intentional agents like the self. This species-unique form of social cognition emerges in human ontogeny at approximately 1 year of age, as infants begin to engage with other persons in various kinds of joint attentional activities involving gaze following, social referencing, and gestural communication. Young children's joint attentional skills then engender some uniquely powerful forms of cultural learning, enabling the acquisition of language, discourse skills, tool-use practices, and other conventional activities. These novel forms of cultural learning allow human beings to, in effect, pool their cognitive resources both contemporaneously and over historical time in ways that are unique in the animal kingdom.
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  • 8
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    Annual Review of Anthropology 28 (1999), S. 531-552 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Optimality theory was introduced in the early 1990s as an alternative model of the organization of natural human language sound systems. This article provides an introduction to the model for the nonlinguist. The basic principles of optimality theory are introduced and explained (GEN, CON, and EVAL). Three important constraint families are explored (Faithfulness, Alignment, and Markedness). Illustrations are provided involving syllabification and vowel harmony in Tibetan and prosodic phonotactics in Tonkawa. The article closes with two general discussions. The first addresses recurring issues in phonological and linguistic analysis and sketches how optimality theory might account for these. The second points out how the explanations arrived at through optimality theory are providing new answers to familiar questions, as well as raising new questions for study.
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  • 9
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    Annual Review of Anthropology 28 (1999), S. 553-575 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Studying human behavior in the light of evolutionary theory involves studying the comparative evolutionary history of behaviors (phylogeny), the psychological machinery that generates them (mechanisms), and the adaptive value of that machinery in past reproductive competition (natural selection). To show the value of a phylogenetic perspective, I consider the ethology of emotional expression and the cladistics of primate social systems. For psychological mechanisms, I review evidence for a pan-human set of conceptual building blocks, including innate concepts of things, space, and time, of number, of logic, of natural history, and of "other minds" and social life, which can be combined to generate a vast array of culture-specific concepts. For natural selection, I discuss the sexual selection of sex differences and similarities, and the social selection of moral sentiments and group psychology.
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  • 10
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    Annual Review of Anthropology 28 (1999), S. 577-598 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract As an artifact of imperial culture, Africanist anthropology is historically associated with the colonization of Africa in ways that undermine the subdiscipline's claims of neutrality and objectivity. A critical literature on the ideological and discursive inventions of Africa by the West challenges the very possibility of Africanist anthropology, to which a variety of responses have emerged. These range from historical reexaminations of imperial discourses, colonial interactions, and fieldwork in Africa, including dialogical engagements with the very production of ethnographic texts, to a more dialectical anthropology of colonial spectacle and culture as it was coproduced and reciprocally determined in imperial centers and peripheries. Understood philologically, as an imperial palimpsest in ethnographic writing, the colonial legacy in Africanist ethnography can never be negated, but must be acknowledged under the sign of its erasure.
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  • 11
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 183-229 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract Recent developments in the application of K-Ar and 40Ar/39Ar dating of continental weathering process demonstrate the method's suitability for dating minerals present in weathering profiles. Alunite-group sulfates and hollandite-group manganese oxides, which often precipitate through weathering reactions, were first analyzed by the K-Ar method 30 years ago. Recently these minerals were shown to be suitable to 40Ar/39Ar geochronology, despite their fine-grained habits. The bulk nature of the K-Ar technique and the complex mineral assemblages in weathering profiles restrict K-Ar dating of weathering processes. The single-crystal approach possible with the 40Ar/39Ar method allows the study of weathering profiles where alunite- and hollandite-group minerals occur as minor phases. Step-heating analysis possible with the 40Ar/39Ar method provides information about the Ar and K retention histories, the presence of hypogene contaminants, and possible 39Ar recoil during sample irradiation. Fully automated, modern 40Ar/39Ar systems enable analysis of several samples, providing a comprehensive weathering database. These results are useful in the study of continental paleoclimates and the geochemical, geomorphological, and tectonic histories of an area.
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  • 12
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 359-384 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract In this paper, an overview is presented of coupled processes linking thermo-hydro-mechanical (THM) effects in fractured rocks. A formulation is first presented to show the linkage mathematically, which can be used as a basis for numerical solutions and for further developments. Two simple examples of hydromechanical (HM) and thermo-hydro-mechanical (THM) coupled processes are discussed to convey physical insight into such couplings. Finally, three large-scale, long-term experiments currently under way are described. These are being conducted specifically to study coupled processes in situ.
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  • 13
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 313-358 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract Stromatolites are attached, lithified sedimentary growth structures, accretionary away from a point or limited surface of initiation. Though the accretion process is commonly regarded to result from the sediment trapping or precipitation-inducing activities of microbial mats, little evidence of this process is preserved in most Precambrian stromatolites. The successful study and interpretation of stromatolites requires a process-based approach, oriented toward deconvolving the replacement textures of ancient stromatolites. The effects of diagenetic recrystallization first must be accounted for, followed by analysis of lamination textures and deduction of possible accretion mechanisms. Accretion hypotheses can be tested using numerical simulations based on modern stromatolite growth processes. Application of this approach has shown that stromatolites were originally formed largely through in situ precipitation of laminae during Archean and older Proterozoic times, but that younger Proterozoic stromatolites grew largely through the accretion of carbonate sediments, most likely through the physical process of microbial trapping and binding. This trend most likely reflects long-term evolution of the earth's environment rather than microbial communities.
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  • 14
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 463-493 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract The history of carnivorous mammals is characterized by a series of rise-and-fall patterns of diversification in which declining clades are replaced by phylogenetically distinct but functionally similar clades. Seven such examples from the last 46 million years are described for North America and Eurasia. In three of the seven turnover events, competition with replacement taxa may have driven the decline of formerly dominant taxa. In the remaining four this is less likely because inferred functional similarity was minimal during the interval of temporal overlap between clades. However, competition still may have been important in producing the rise-and-fall pattern through suppression of evolution within replacement taxa; as long as the large carnivore ecospace was filled, the radiation of new taxa into that ecospace was limited, only occurring after the extinction of the incumbents. The apparently inevitable decline of incumbent taxa may reflect the tendency for clades of large carnivorous mammals to produce more specialized species as they mature, leading to increased vulnerability to extinction when environments change.
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  • 15
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    Annual Review of Neuroscience 22 (1999), S. 49-103 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Dr. Thomas PS Powell was one of the founders of modern neuroanatomy. His career spanned an era that saw techniques for analyzing connections in the central nervous system dramatically increase in number and resolving power. In tracing the history of his research, one can see how the introduction of each new technique provided an incremental step in analytical capacity although eventually revealing its own limitations. Also evident is the extent to which prejudices born in the days of applying earlier techniques could continue to influence the interpretation of results obtained with new ones. Powell's contributions to neuroscience were extremely wide-ranging, encompassing investigations of the circuitry of the basal ganglia, corticofugal connections, topographic maps in sensory systems, central olfactory pathways, corticocortical and commissural connections, and pathways for sensory convergence in the cerebral cortex. From these investigations, made with tract tracing techniques, much existing knowledge of forebrain organization is derived. He was also one of the earliest investigators to use electron microscopy in the investigation of the central nervous system, and his electron microscopic studies on the olfactory bulb, thalamus, cerebral cortex, and basal ganglia laid, to a large extent, the foundations for all modern research on the synaptic circuitry of these structures. He was given to synthesizing data across systems in order to arrive at common principles of brain organization. A number of these syntheses have been sources of great interest and, occasionally, controversy.
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    Annual Review of Neuroscience 22 (1999), S. 123-144 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Parkinson's disease (PD) is an age-related neurodegenerative disorder that affects approximately 1 million persons in the United States. It is characterized by resting tremor, rigidity, bradykinesia or slowness, gait disturbance, and postural instability. Pathological features include degeneration of dopaminergic neurons in the substantia nigra pars compacta coupled with intracytoplasmic inclusions known as Lewy bodies. Neurodegeneration and Lewy bodies can also be found in the locus ceruleus, nucleus basalis, hypothalamus, cerebral cortex, cranial nerve motor nuclei, and central and peripheral components of the autonomic nervous system. Current treatment consists of a dopamine replacement strategy using primarily the dopamine precursor levodopa. While levodopa provides benefit to virtually all PD patients, after 5-10 years of treatment the majority of patients develop adverse events in the form of dyskinesia (involuntary movements) and fluctuations in motor response. Further, disease progression is associated with the development of dementia, autonomic dysfunction, and postural instability, which do not respond to levodopa therapy. Accordingly, research efforts have been directed toward understanding the etiology and pathogenesis of PD in the hope of developing a more effective therapy that will slow or halt the natural progression of PD. This paper reviews recent advances.
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    Annual Review of Neuroscience 22 (1999), S. 261-294 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The generation of distinct classes of neurons at defined positions within the developing vertebrate nervous system depends on inductive signals provided by local cell groups that act as organizing centers. Genetic and embryological studies have begun to elucidate the processes that control the pattern and identity of neuronal cell types. Here we discuss the cellular interactions and molecular mechanisms that direct neuronal cell fates in the dorsal half of the vertebrate central nervous system. The specification of dorsal neuronal cell fates appears to depend on a cascade of inductive signals initiated by cells of the epidermal ectoderm that flank the neural plate and propagated by roof plate cells within the neural tube. Members of the transforming growth factor-beta (TGFbeta) family of secreted proteins have a prominent role in mediating these dorsalizing signals. Additional signals involving members of the Wnt and fibroblast growth factor (FGF) families may also contribute to the proliferation and differentiation of dorsal neuronal cell types.
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  • 18
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    Annual Review of Immunology 17 (1999), S. 331-367 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Four members of the tumor necrosis factor (TNF) ligand family, TNF-alpha, LT-alpha, LT-beta, and LIGHT, interact with four receptors of the TNF/nerve growth factor family, the p55 TNF receptor (CD120a), the p75 TNF receptor (CD120b), the lymphotoxin beta receptor (LTbetaR), and herpes virus entry mediator (HVEM) to control a wide range of innate and adaptive immune response functions. Of these, the most thoroughly studied are cell death induction and regulation of the inflammatory process. Fas/Apo1 (CD95), a receptor of the TNF receptor family activated by a distinct ligand, induces death in cells through mechanisms shared with CD120a. The last four years have seen a proliferation in knowledge of the proteins participating in the signaling by the TNF system and CD95. The downstream signaling molecules identified so far-caspases, phospholipases, the three known mitogen activated protein (MAP) kinase pathways, and the NF-kappaB activation cascade-mediate the effects of other inducers as well. However, the molecules that initiate these signaling events, including the death domain- and TNF receptor associated factor (TRAF) domain-containing adapter proteins and the signaling enzymes associated with them, are largely unique to the TNF/nerve growth factor receptor family.
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    Annual Review of Immunology 17 (1999), S. 89-108 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The initiation of biochemical signal transduction following ligation of surface receptors with intrinsic cytoplasmic tyrosine kinase activity is common for many cell types. T lymphocytes also require activation of tyrosine kinases following T cell receptor (TCR) ligation for maximal stimulation. However, the TCR has no intrinsic tyrosine kinase activity. Instead, the TCR must rely on cytoplasmic tyrosine kinases that localize to the TCR complex and initiate TCR-mediated signaling events. Although much has been learned regarding how these cytosolic tyrosine kinases are activated and recruited to the TCR complex, relatively little is understood about how these initial events are translated into transcriptional activation of genes that regulate cytokine production, cell proliferation, and cell death. Recently, it has become clear that the class of intracellular molecules known collectively as adapter proteins, molecules with modular domains capable of recruiting additional proteins but that exhibit no intrinsic enzymatic activity, serve to couple proximal biochemical events initiated by TCR ligation with more distal signaling pathways.
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    Annual Review of Immunology 17 (1999), S. 189-220 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Natural killer (NK) cells are populations of lymphocytes that can be activated to mediate significant levels of cytotoxic activity and produce high levels of certain cytokines and chemokines. NK cells respond to and are important in defense against a number of different infectious agents. The first indications for this function came from the observations that virus-induced interferons alpha/beta (IFN-alpha and -beta) are potent inducers of NK cell-mediated cytotoxicity, and that NK cells are important contributors to innate defense against viral infections. In addition to IFN-alpha/beta, a wide range of other innate cytokines can mediate biological functions regulating the NK cell responses of cytotoxicity, proliferation, and gamma interferon (IFN-gamma) production. Certain, but not all, viral infections induce interleukin 12 (IL-12) to elicit NK cell IFN-gamma production and antiviral mechanisms. However, high levels of IFN-alpha/beta appear to be unique and/or uniquely dominant in the context of viral infections and act to regulate other innate responses, including induction of NK cell proliferation in vivo and overall negative regulation of IL-12 production. A detailed picture is developing of particular innate cytokines activating NK cell responses and their consorted effects in providing unique endogenous milieus promoting downstream adaptive responses, most beneficial in defense against viral infections.
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    Annual Review of Immunology 17 (1999), S. 109-147 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract This review addresses issues related to the evolution of the complex multigene families of antigen binding receptors that function in adaptive immunity. Advances in molecular genetic technology now permit the study of immunoglobulin (Ig) and T cell receptor (TCR) genes in many species that are not commonly studied yet represent critical branch points in vertebrate phylogeny. Both Ig and TCR genes have been defined in most of the major lineages of jawed vertebrates, including the cartilaginous fishes, which represent the most phylogenetically divergent jawed vertebrate group relative to the mammals. Ig genes in cartilaginous fish are encoded by multiple individual loci that each contain rearranging segmental elements and constant regions. In some loci, segmental elements are joined in the germline, i.e. they do not undergo genetic rearrangement. Other major differences in Ig gene organization and the mechanisms of somatic diversification have occurred throughout vertebrate evolution. However, relating these changes to adaptive immune function in lower vertebrates is challenging. TCR genes exhibit greater sequence diversity in individual segmental elements than is found in Ig genes but have undergone fewer changes in gene organization, isotype diversity, and mechanisms of diversification. As of yet, homologous forms of antigen binding receptors have not been identified in jawless vertebrates; however, acquisition of large amounts of structural data for the antigen binding receptors that are found in a variety of jawed vertebrates has defined shared characteristics that provide unique insight into the distant origins of the rearranging gene systems and their relationships to both adaptive and innate recognition processes.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 47-65 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract In plants the biosynthesis of prenyllipids and isoprenoids proceeds via two independent pathways: (a) the cytosolic classical acetate/mevalonate pathway for the biosynthesis of sterols, sesquiterpenes, triterpenoids; and (b) the alternative, non-mevalonate 1-deoxy-d-xylulose-5-phosphate (DOXP) pathway for the biosynthesis of plastidic isoprenoids, such as carotenoids, phytol (a side-chain of chlorophylls), plastoquinone-9, isoprene, mono-, and diterpenes. Both pathways form the active C5-unit isopentenyl diphosphate (IPP) as the precursor from which all other isoprenoids are formed via head-to-tail addition. This review summarizes current knowledge of the novel 1-deoxy-d-xylulose-5-phosphate (DOXP) pathway for isopentenyl diphosphate biosynthesis, apparently located in plastids. The DOXP pathway of IPP formation starts from D-glyceraldehyde-3-phosphate (GA-3-P) and pyruvate, with DOXP-synthase as the starting enzyme. This pathway provides new insight into the regulation of chloroplast metabolism.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 187-217 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract C4 plants, including maize, Flaveria, amaranth, sorghum, and an amphibious sedge Eleocharis vivipara, have been employed to elucidate the molecular mechanisms and signaling pathways that control C4 photosynthesis gene expression. Current evidence suggests that pre-existing genes were recruited for the C4 pathway after acquiring potent and surprisingly diverse regulatory elements. This review emphasizes recent advances in our understanding of the creation of C4 genes, the activities of the C4 gene promoters consisting of synergistic and combinatorial enhancers and silencers, the use of 5' and 3' untranslated regions for transcriptional and posttranscriptional regulations, and the function of novel transcription factors. The research has also revealed new insights into unique or universal mechanisms underlying cell-type specificity, coordinate nuclear-chloroplast actions, hormonal, metabolic, stress and light responses, and the control of enzymatic activities by phosphorylation and reductive processes.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 245-276 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract The past few decades have witnessed exciting progress in studies on the biosynthesis of cellulose. In the bacterium Acetobacter xylinum, discovery of the activator of the cellulose synthase, cyclic diguanylic acid, opened the way for obtaining high rates of in vitro synthesis of cellulose. This, in turn, led to purification of the cellulose synthase and for the cloning of genes that encode the catalytic subunit and other proteins that bind the activator and regulate its synthesis and degradation, or that control secretion and crystallization of the microfibrils. In higher plants, a family of genes has been discovered that show interesting similarities and differences from the gene in bacteria that encodes the catalytic subunit of the synthase. Genetic evidence now supports the concept that members of this family encode the catalytic subunit in these organisms, with various members showing tissue-specific expression. Although the cellulose synthase has not yet been purified to homogeneity from plants, recent progress in this area suggests that this will soon be accomplished.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 333-359 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract The involvement of excited and highly reactive intermediates in oxygenic photosynthesis poses unique problems for algae and plants in terms of potential oxidative damage to the photosynthetic apparatus. Photoprotective processes prevent or minimize generation of oxidizing molecules, scavenge reactive oxygen species efficiently, and repair damage that inevitably occurs. This review summarizes several photoprotective mechanisms operating within chloroplasts of plants and green algae. The recent use of genetic and molecular biological approaches is providing new insights into photoprotection, especially with respect to thermal dissipation of excess absorbed light energy, alternative electron transport pathways, chloroplast antioxidant systems, and repair of photosystem II.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 419-446 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Leaves are produced in succession on the shoot apical meristem (SAM) of a plant. The three landmark stages in leaf morphogenesis include initiation, acquisition of suborgan identities, and tissue differentiation. The expression of various genes relative to these steps in leaf morphogenesis is described. KNOTTED-like homeobox (KNOX) genes, FLO/LFY, and floral homeotic genes may be involved in generation of leaf shape and complexity. The differences between compound leaves and simple leaves in gene expression characteristics and morphogenetic patterns are discussed.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 539-570 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Many microorganisms possess inducible mechanisms that concentrate CO2 at the carboxylation site, compensating for the relatively low affinity of Rubisco for its substrate, and allowing acclimation to a wide range of CO2 concentrations. The organization of the carboxysomes in prokaryotes and of the pyrenoids in eukaryotes, and the presence of membrane mechanisms for inorganic carbon (Ci) transport, are central to the concentrating mechanism. The presence of multiple Ci transporting systems in cyanobacteria has been indicated. Certain genes involved in structural organization, Ci transport and the energization of the latter have been identified. Massive Ci fluxes associated with the CO2-concentrating mechanism have wide-reaching ecological and geochemical implications.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 641-664 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Silicon is present in plants in amounts equivalent to those of such macronutrient elements as calcium, magnesium, and phosphorus, and in grasses often at higher levels than any other inorganic constituent. Yet except for certain algae, including prominently the diatoms, and the Equisetaceae (horsetails or scouring rushes), it is not considered an essential element for plants. As a result it is routinely omitted from formulations of culture solutions and considered a nonentity in much of plant physiological research. But silicon-deprived plants grown in conventional nutrient solutions to which silicon has not been added are in many ways experimental artifacts. They are often structurally weaker than silicon-replete plants, abnormal in growth, development, viability, and reproduction, more susceptible to such abiotic stresses as metal toxicities, and easier prey to disease organisms and to herbivores ranging from phytophagous insects to mammals. Many of these same conditions afflict plants in silicon-poor soils-and there are such. Taken together, the evidence is overwhelming that silicon should be included among the elements having a major bearing on plant life.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 695-718 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract The root system of a plant is as complicated as the shoot in its diversity, in its reactions with the matrix of substances, and with the myriad organisms that surround it. Laboratory studies blind us to the complexity found by careful study of roots in soil. This complexity is illustrated in the much-studied corn root system, covering the changes along the framework roots: the surface tissues and their interactions with the soil, the water-conducting xylem, whose gradual elaboration dictates the water status of the root. A conspicuous manifestation of the changes is the rhizosheath, whose microflora differs from that on the mature bare zones. The multitude of fine roots is the most active part of the system in acquiring water and nutrients, with its own multitude of root tips, sites of intense chemical activity, that strongly modify the soil they contact, mobilize reluctant ions, immobilize toxic ions, coat the soil particles with mucilage, and select the microflora.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 1-32 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Many cellular processes require a balance between protein synthesis and protein degradation. The vacuole/lysosome is the main site of protein and organellar turnover within the cell due to its ability to sequester numerous hydrolases within a membrane-enclosed compartment. Several mechanisms are used to deliver substrates, as well as resident hydrolases, to this organelle. The delivery processes involve dynamic rearrangements of membrane. In addition, continual adjustments are made to respond to changes in environmental conditions. In this review, we focus on recent progress made in analyzing these delivery processes at a molecular level. The identification of protein components involved in the recognition, sequestration, and transport events has begun to provide information about this important area of eukaryotic cell physiology.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 81-112 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The neural crest is a transient population of multipotent precursor cells named for its site of origin at the crest of the closing neural folds in vertebrate embryos. Following neural tube closure, these cells become migratory and populate diverse regions throughout the embryo where they give rise to most of the neurons and support cells of the peripheral nervous system (PNS), pigment cells, smooth muscle, craniofacial cartilage, and bone. Because of its remarkable ability to generate such diverse derivatives, the neural crest has fascinated developmental biologists for over one hundred years. A great deal has been learned about the migratory pathways neural crest cells follow and the signals that may trigger their differentiation, but until recently comparatively little was known about earlier steps in neural crest development. In the past few years progress has been made in understanding these earlier events, including how the precursors of these multipotent cells are specified in the early embryo and the mechanisms by which they become migratory. In this review, we first examine the mechanisms underlying neural crest induction, paying particular attention to a number of growth factor and transcription factor families that have been implicated in this process. We also discuss when and how the fate of neural crest precursors may diverge from those of nearby neural and epidermal populations. Finally, we review recent advances in our understanding of how neural crest cells become migratory and address the process of neural crest diversification.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 231-268 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The Drosophila phototransduction cascade has emerged as an attractive paradigm for understanding the molecular mechanisms underlying visual transduction, as well as other G protein-coupled signaling cascades that are activated and terminated with great rapidity. A large collection of mutants affecting the fly visual cascade have been isolated, and the nature and function of many of the affected gene products have been identified. Virtually all of the proteins, including those that were initially classified as novel, are highly related to vertebrate homologs. Recently, it has become apparent that most of the proteins central to Drosophila phototransduction are coupled into a supramolecular signaling complex, signalplex, through association with a PDZ-containing scaffold protein. The characterization of this complex has led to a re-evaluation of the mechanisms underlying the activation and deactivation of the phototransduction cascade.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 291-339 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Information can be transferred between the nucleus and the cytoplasm by translocating macromolecules across the nuclear envelope. Communication of extracellular or intracellular changes to the nucleus frequently leads to a transcriptional response that allows cells to survive in a continuously changing environment. Eukaryotic cells have evolved ways to regulate this movement of macromolecules between the cytoplasm and the nucleus such that the transfer of information occurs only under conditions in which a transcriptional response is required. This review focuses on the ways in which cells regulate movement of proteins across the nuclear envelope and the significance of this regulation for controlling diverse biological processes.
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    Annual Review of Biochemistry 68 (1999), S. 287-300 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract An RNA motif is a discrete sequence or combination of base juxtapositions found in naturally occurring RNAs in unexpectedly high abundance. Because all the motifs examined so far have three-dimensional structures independent of the context in which they are embedded, they are important components of the "kit" of structural elements from which RNAs are constructed. This review discusses the structures of the motifs that have been identified so far and speculates on the importance of their role in determining RNA conformation and their evolutionary origin.
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    Annual Review of Biochemistry 68 (1999), S. 301-319 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract Eukaryotic mRNA synthesis is catalyzed by multisubunit RNA polymerase II and proceeds through multiple stages referred to as preinitiation, initiation, elongation, and termination. Over the past 20 years, biochemical studies of eukaryotic mRNA synthesis have largely focused on the preinitiation and initiation stages of transcription. These studies led to the discovery of the class of general initiation factors (TFIIB, TFIID, TFIIE, TFIIF, and TFIIH), which function in intimate association with RNA polymerase II and are required for selective binding of polymerase to its promoters, formation of the open complex, and synthesis of the first few phosphodiester bonds of nascent transcripts. Recently, biochemical studies of the elongation stage of eukaryotic mRNA synthesis have led to the discovery of several cellular proteins that have properties expected of general elongation factors and that have been found to play unanticipated roles in human disease. Among these candidate general elongation factors are the positive transcription elongation factor b (P-TEFb), eleven-nineteen lysine-rich in leukemia (ELL), Cockayne syndrome complementation group B (CSB), and elongin proteins, which all function in vitro to expedite elongation by RNA polymerase II by suppressing transient pausing or premature arrest by polymerase through direct interactions with the elongation complex. Despite their similar activities in elongation, the P-TEFb, ELL, CSB, and elongin proteins appear to play roles in a diverse collection of human diseases, including human immunodeficiency virus-1 infection, acute myeloid leukemia, Cockayne syndrome, and the familial cancer predisposition syndrome von Hippel-Lindau disease. Here we review our current understanding of the P-TEFb, ELL, CSB, and elongin proteins, their mechanisms of action, and their roles in human disease.
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    Annual Review of Biochemistry 68 (1999), S. 425-458 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract The high water permeability characteristic of mammalian red cell membranes is now known to be caused by the protein AQP1. This channel freely permits movement of water across the cell membrane, but it is not permeated by other small, uncharged molecules or charged solutes. AQP1 is a tetramer with each subunit containing an aqueous pore likened to an hourglass formed by obversely arranged tandem repeats. Cryoelectron microscopy of reconstituted AQP1 membrane crystals has revealed the three-dimensional structure at 3-6 A. AQP1 is distributed in apical and basolateral membranes of renal proximal tubules and descending thin limbs as well as capillary endothelia. Ten mammalian aquaporins have been identified in water-permeable tissues and fall into two groupings. Orthodox aquaporins are water-selective and include AQP2, a vasopressin-regulated water channel in renal collecting duct, in addition to AQP0, AQP4, and AQP5. Multifunctional aquaglyceroporins AQP3, AQP7, and AQP9 are permeated by water, glycerol, and some other solutes. Aquaporins are being defined in numerous other species including amphibia, insects, plants, and microbials. Members of the aquaporin family are implicated in numerous physiological processes as well as the pathophysiology of a wide range of clinical disorders.
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    Annual Review of Biochemistry 68 (1999), S. 187-218 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract Telomerase is a cellular reverse transcriptase specialized for use of a template carried within the RNA component of the enzyme ribonucleoprotein complex. Substrates for telomerase are single-stranded oligonucleotides in vitro and chromosome ends in vivo. In vitro, a bound substrate is extended by an initial round of DNA synthesis on the internal RNA template and in some cases by multiple rounds of template copying before product dissociation. In vivo, de novo synthesis of one strand of a telomeric repeat sequence by telomerase balances the sequence loss resulting from incomplete replication of linear chromosome ends by RNA primer-requiring DNA polymerases. Telomerase biochemistry has been studied extensively by using partially purified cell extracts. Telomerase components are being identified and beginning to be produced in recombinant form. This review focuses on the enzyme mechanism of telomerases from ciliate species, thus far the most intensively studied systems.
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    Annual Review of Entomology 44 (1999), S. 207-231 
    ISSN: 0066-4170
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract The family Anthocoridae (Hemiptera:Heteroptera) contains between 400 and 600 species distributed worldwide, chiefly on the continents but also on oceanic islands. They are small (1.4-4.5 mm) and common to a wide variety of habitats. Many are found in cryptic habitats such as galls, several widespread genera are surface feeders on small arthropods (Anthocoris, Orius, and Tetraphleps), and others can be found in ant nests and, especially, under bark. Wing polymorphism is common in this family, often associated with the cryptic habit. Most known species are predaceous, though some take plant food as well (e.g. Orius insidiosus, Orius pallidicornis). A few of these are believed to be entirely phytophagous (Paratriphleps laeviusculus). Their small size and often generalized feeding habits have resulted in about 30 introduced species, mostly accidental. A few have been introduced deliberately as biological control agents (Anthocoris spp., Montandoniola moraguesi, O. insidiosus, Orius tristicolor, and Tetraphleps spp.). Most nonindigenous species seem to have been distributed as a result of human activities, especially commerce. The predaceous habits of many Anthocoridae have attracted the attention of researchers who work in agroecosystems. Integrated pest management programs often include these predators, which has given us greater knowledge about these species than those found in natural ecosystems. Exciting discoveries about the attractiveness to these bugs of certain volatile plant and arthropod compounds are opening new areas of investigation into their chemical ecology. The reactions of these tiny predators will surely become better understood as a result.
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    Annual Review of Entomology 44 (1999), S. 343-370 
    ISSN: 0066-4170
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Cassava (Manihot esculenta) occupies a uniquely important position as a food security crop for smallholder farmers in areas of the tropics where climate, soils, or societal stresses constrain production. Given its reliability and productivity, cassava is the most important locally produced food in a third of the world's low-income, food-deficit countries. It is the fourth most important source of carbohydrates for human consumption in the tropics, after rice, sugar, and maize. World production of cassava from 1994-1996 averaged 166 million tons/year grown on 16.6 million hectares (ha), for an average yield of 9.9 tons/ha. Approximately 57% is used for human consumption, 32% for animal feed and industrial purposes, and 11% is waste. Africa accounts for 51.3% of the production; Asia, 29.4%; and Latin America, 19.3%. The area planted to cassava in Africa, Asia, and Latin America is 10.3, 3.7, and 2.6 million ha, respectively.
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    Annual Review of Entomology 44 (1999), S. 77-96 
    ISSN: 0066-4170
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Pigeonpea (Cajanus cajan) is an important crop in semi-arid tropical and subtropical farming systems, providing high quality vegetable protein, animal feed, and firewood. Insect pests feeding on flowers, pods, and seeds are the most important biotic constraint affecting pigeonpea yields. This review summarizes the biology and ecology of the three most important groups of pests: flower- and pod-feeding Lepidoptera, pod-sucking Hemiptera, and seed-feeding Diptera and Hymenoptera. Recent research investigating the complex interactions among pigeonpea, its key pests, and their natural enemies is also reviewed. These relationships have implications on the pest status of individual species and on possible control strategies. Pigeonpea pest management research has focused until recently on the identification and development of resistant cultivars and on chemical control. Future research must focus on environmentally sound pest management strategies that are compatible with the needs and limitations of pigeonpea farmers. Several priority areas for research are suggested.
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    Annual Review of Physiology 61 (1999), S. 143-167 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Angina pectoris often results from ischemic episodes that excite chemosensitive and mechanoreceptive receptors in the heart. Ischemic episodes release a collage of chemicals, including adenosine and bradykinin, that excites the receptors of the sympathetic and vagal afferent pathways. Sympathetic afferent fibers from the heart enter the upper thoracic spinal cord and synapse on cells of origin of ascending pathways. This review focuses on the spinothalamic tract, but other pathways are excited as well. Excitation of spinothalamic tract cells in the upper thoracic and lower cervical segments, except C7 and C8 segments, contributes to the anginal pain experienced in the chest and arm. Cardiac vagal afferent fibers synapse in the nucleus tractus solitarius of the medulla and then descend to excite upper cervical spinothalamic tract cells. This innervation contributes to the anginal pain experienced in the neck and jaw. The spinothalamic tract projects to the medial and lateral thalamus and, based on positron emission tomography studies, activates several cortical areas, including the anterior cingulate gyrus (BA 24 and 25), the lateral basal frontal cortex, and the mesiofrontal cortex.
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    Annual Review of Physiology 61 (1999), S. 193-217 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Secreted by the heart, more specifically by atrial cardiomyocytes under normal conditions but also by ventricular myocytes during cardiac hypertrophy, natriuretic peptides are now considered important hormones in the control of blood pressure and salt and water excretion. Studies on natriuretic peptide secretagogues and their mechanisms of action have been complicated by hemodynamic changes and contractions to which the atria are constantly subjected. It now appears that atrial stretch through mechano-sensitive ion channels, adrenergic stimulation via alpha1A-adrenergic receptors, and endothelin via its ETA receptor subtype are major triggering agents of natriuretic peptide release. With several other stimuli, such as angiotensin II and beta-adrenergic agents, modulation of natriuretic peptide release appears to be linked to local generation of prostaglandins. In all cases, intracellular calcium homeostasis, controlled by several ion channels, is considered a key element in the regulation of natriuretic peptide secretion.
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    Annual Review of Physiology 61 (1999), S. 311-335 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Subcellularly localized Ca2+ signals in cardiac and skeletal muscle have recently been identified as elementary Ca2+ signaling events. The signals, termed Ca2+ sparks and Ca2+ quarks, represent openings of Ca2+ release channels located in the membrane of the sarcoplasmic reticulum (SR). In cardiac muscle, the revolutionary discovery of Ca2+ sparks has allowed the development of a fundamentally different concept for the amplification of Ca2+ signals by Ca2+-induced Ca2+ release. In such a system, a graded amplification of the triggering Ca2+ signal entering the myocyte via L-type Ca2+ channels is accomplished by a recruitment process whereby individual SR Ca2+ release units are locally controlled by L-type Ca2+ channels. In skeletal muscle, the initial SR Ca2+ release is governed by voltage-sensors but subsequently activates additional Ca2+ sparks by Ca2+-induced Ca2+ release from the SR. Results from studies on elementary Ca2+ release events will improve our knowledge of muscle Ca2+ signaling at all levels of complexity, from the molecule to normal cellular function, and from the regulation of cardiac and skeletal muscle force to the pathophysiology of excitation-contraction coupling.
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    Annual Review of Physiology 61 (1999), S. 363-389 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Two potent hypotensive peptides, adrenomedullin (AM) and proadrenomedullin N-terminal 20 peptide (PAMP), are encoded by the adrenomedullin gene. AM stimulates nitric oxide production by endothelial cells, whereas PAMP acts presynaptically to inhibit adrenergic nerves that innervate blood vessels. Complementary, but mechanistically unique, actions also occur in the anterior pituitary gland where both peptides inhibit adrenocorticotropin release. In the adrenal gland both AM and PAMP inhibit potassium and angiotensin II-stimulated aldosterone secretion. Natriuretic and diuretic actions of AM reflect unique actions of the peptide on renal blood flow and tubular function. In the brain AM inhibits water intake and, in a physiologically relevant manner, salt appetite. Both AM and PAMP act in the brain to elevate sympathetic tone, effects that mirror the positive inotropic action of AM in the heart. Cardioprotective actions in the brain and heart may be important counter-regulatory actions that buffer the extreme hypotensive actions of the peptides when released in sepsis. Thus the biologic actions of the proadrenomedullin-derived peptides seem well coordinated to contribute to the physiologic regulation of volume and electrolyte homeostasis.
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    Annual Review of Physiology 61 (1999), S. 573-592 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Vertebrate lungs have long been thought to have evolved in fishes largely as an adaptation for life in hypoxic water. This view overlooks the possibility that lungs may have functioned to supply the heart with oxygen and may continue to serve this function in extant fishes. The myocardium of most vertebrates is avascular and obtains oxygen from luminal blood. Because oxygen-rich pulmonary blood mixes with oxygen-poor systemic blood before entering the heart of air-breathing fishes, lung ventilation may supply the myocardium with oxygen and expand aerobic exercise capabilities. Although sustained exercise in tetrapods is facilitated by septation of the heart and the formation of a dual pressure system, a divided cardio-pulmonary system may conflict with myocardial oxygenation because the right side of the heart is isolated from pulmonary oxygen. This may have contributed to the evolution of the coronary circulation.
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    Annual Review of Physiology 61 (1999), S. 593-625 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract The mouse is an ideal species for investigation at the interface of lung biology and lung function. As detailed in this review, there are well-developed methods for the quantitative study of lung function in mice. These methods can be applied to mice in both terminal and nonterminal experiments. Terminal experimental approaches provide more detailed physiological information, but nonterminal measurements provide adequate data for certain experiments. In this review, we provide two examples of how these models can be used to further understanding of the primary pathobiology of airway responsiveness in both the absence and the presence of induced airway inflammation. The first model is a dissection of chromosomal loci linked to the variance in airway responsiveness observed in the absence of any manipulation to induce airway inflammation. The second model explores the role of T-cell costimulatory signals in the induction of airway hyperresponsiveness. As the number of mice with targeted deletions of effector genes or insertion of informative transgenes grows, additional examples are likely to accrue.
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    Annual Review of Physiology 61 (1999), S. 663-682 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Krebs cycle intermediates such as succinate, citrate, and alpha-ketoglutarate are transferred across plasma membranes of cells by secondary active transporters that couple the downhill movement of sodium to the concentrative uptake of substrate. Several transporters have been identified in isolated membrane vesicles and cells based on their functional properties, suggesting the existence of at least three or more Na+/dicarboxylate cotransporter proteins in a given species. Recently, several cDNAs, called NaDC-1, coding for the low-affinity Na+/dicarboxylate cotransporters have been isolated from rabbit, human, and rat kidney. The Na+/dicarboxylate cotransporters are part of a distinct gene family that includes the renal and intestinal Na+/sulfate cotransporters. Other members of this family include a Na+- and Li+-dependent dicarboxylate transporter from Xenopus intestine and a putative Na+/dicarboxylate cotransporter from rat intestine. The current model of secondary structure in NaDC-1 contains 11 transmembrane domains and an extracellular N-glycosylated carboxy terminus.
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    Annual Review of Physiology 61 (1999), S. 627-661 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract At birth, fetal distal lung epithelial (FDLE) cells switch from active chloride secretion to active sodium (Na+) reabsorption. Sodium ions Senter the FDLE and alveolar type II (ATII) cells mainly through apical nonselective cation and Na+-selective channels, with conductances of 4-26 pS (picoSiemens) in FDLE and 20-25 pS in ATII cells. All these channels are inhibited by amiloride with a 50% inhibitory concentration of 〈1 muM, and some are also inhibited by [N-ethyl-N-isopropyl]-2'-4'-amiloride (50% inhibitory concentration of 〈1 muM). Both FDLE and ATII cells contain the alpha-, beta-, and gamma-rENaC (rat epithelial Na+ channels) mRNAs; reconstitution of an ATII cell Na+-channel protein into lipid bilayers revealed the presence of 25-pS Na+ single channels, inhibited by amiloride and [N-ethyl-N-isopropyl]-2'-4'-amiloride. A variety of agents, including cAMP, oxygen, glucocorticoids, and in some cases Ca2+, increased the activity and/or rENaC mRNA levels. The phenotypic properties of these channels differ from those observed in other Na+-absorbing epithelia. Pharmacological blockade of alveolar Na+ transport in vivo, as well as experiments with newborn alpha-rENaC knock-out mice, demonstrate the importance of active Na+ transport in the reabsorption of fluid from the fetal lung and in reabsorbing alveolar fluid in the injured adult lung. Indeed, in a number of inflammatory diseases, increased production of reactive oxygen-nitrogen intermediates, such as peroxynitrite (ONOO-), may damage ATII and FDLE Na+ channels, decrease Na+ reabsorption in vivo, and thus contribute to the formation of alveolar edema.
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    Annual Review of Physiology 61 (1999), S. 809-834 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Mechanosensory hair cells of the vertebrate inner ear contribute to acoustic tuning through feedback processes involving voltage-gated channels in the basolateral membrane and mechanotransduction channels in the apical hair bundle. The specific number and kinetics of calcium-activated (BK) potassium channels determine the resonant frequency of electrically tuned hair cells. Kinetic variation among BK channels may arise through alternative splicing of slo gene mRNA and combination with modulatory beta subunits. The number of transduction channels and their rate of adaptation rise with hair cell response frequency along the cochlea's tonotopic axis. Calcium-dependent feedback onto transduction channels may underlie active hair bundle mechanics. The relative contributions of electrical and mechanical feedback to active tuning of hair cells may vary as a function of sound frequency.
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    Annual Review of Physiology 61 (1999), S. 873-900 
    ISSN: 0066-4278
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Medicine , Biology
    Notes: Abstract Taste receptor cells respond to gustatory stimuli using a complex arrangement of receptor molecules, signaling cascades, and ion channels. When stimulated, these cells produce action potentials that result in the release of neurotransmitter onto an afferent nerve fiber that in turn relays the identity and intensity of the gustatory stimuli to the brain. A variety of mechanisms are used in transducing the four primary tastes. Direct interaction of the stimuli with ion channels appears to be of particular importance in transducing stimuli reported as salty or sour, whereas the second messenger systems cyclic AMP and inositol trisphosphate are important in transducing bitter and sweet stimuli. In addition to the four basic tastes, specific mechanisms exist for the amino acid glutamate, which is sometimes termed the fifth primary taste, and for fatty acids, a so-called nonconventional taste stimulus. The emerging picture is that not only do individual taste qualities use more than one mechanism, but multiple pathways are available for individual tastants as well.
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    Annual Review of Anthropology 28 (1999), S. 1-25 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract The interaction of nutritional status with political structure in prehistoric New World societies is examined through bioarchaeological analysis. Overall, a general correlation is seen between political complexity and patterns of morbidity among various subsegments of the population. This relationship is strongest among egalitarian societies, in which few differences exist, and state-level societies, in which differences are readily apparent and appear to widen over time. At intermediate levels of political complexity, a less consistent picture emerges; various explanations are considered as to why the dietary differences predicted by the ethnohistorical and archaeological records are not reflected in the osteological record. Also addressed are patterns of differences in access to nutritional resources by gender at the various levels of political organization, as well as patterns of access between rural and urban centers. Future directions of study are suggested.
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    Annual Review of Anthropology 28 (1999), S. 311-339 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Primatology in anthropology began with morphological comparisons of primates to reconstruct the evolution of humans. Naturalistic studies started in the mid-twentieth century and contributed to understanding the functions of morphological variations. Today, research in primatology employs the new paradigm of behavioral ecology and sociobiology for analysis and interpretation of variation in behavior and ecology. Grouping and group sizes of primates are explained with reference to effects of predation, defense of resources, and female defense against male infanticide. Primates avoid close consanguineous mating, usually by dispersal of males from the birthplace, though in bonobos and chimpanzees males are philopatric. In many primates, nepotistic relations among females are explained by kin selection operating on the philopatric sex. In chimpanzees, nepotism is clearest among the philopatric males. Sexual dimorphism, dominance hierarchies, intrasexual competition, and particularly infanticide by males are best explained by the action of sexual selection. Comparative studies of primates indicate that the large brains of the genus Homo (enlarged cerebral cortex) evolved after bipedalism and human dental characters and probably depended on high-quality diets. Broad comparative studies have supported the hypothesis that large brains may have evolved in response to complex social environments, but comparisons within the apes only may not support the hypothesis. Although dominant themes of current anthropology are not compatible with the epistemology, theory, or methodology of primate research and interpretation, primate studies fit easily within the future of anthropology as a four-field evolutionary study of the origins of humans and human nature.
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    Annual Review of Anthropology 28 (1999), S. 285-310 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Apocalypticism and millennialism are the dark and light sides of a historical sensibility transfixed by the possibility of imminent catastrophe, cosmic redemption, spiritual transformation, and a new world order. This essay briefly surveys work by anthropologists and like-minded scholars that focuses directly on endtime movements. It then reviews at more length a varied literature focusing on American apocalypticisms and millennialisms. Turning to contemporary America, we survey the ways in which an apocalyptic/millennial sensibility-as a mode of attention, mode of knowing, and voice-has come to inhabit and structure modern American life across a wide range of registers.
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    Annual Review of Anthropology 28 (1999), S. 341-373 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract This review describes a paradigmatic shift in anthropological studies of human movement, from an observationist view of behavior to a conception of body movement as dynamically embodied action. After outlining the scope of such study, historical and cultural reasons for the relative neglect of body movement in anthropological enquiry are examined critically and placed in the wider context of recent social and cultural theorizing about the body and the problem of dynamic embodiment. A historical overview situates earlier approaches, such as kinesics and proxemics, in relation to more recent developments in theory and method, such as those offered by semasiology and the concept of the "action sign." Overlapping interests with linguistic and cognitive anthropology are described. The emergence of a holistic "anthropology of human movement" has raised new research questions that require new resources. Theoretical insights have challenged researchers to devise new methods and to adopt or devise new technologies, such as videotape and an adequate transcription system. An example of the latter illustrates the analytic advantages of literacy in the medium.
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    Annual Review of Anthropology 28 (1999), S. 375-395 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Issues in the linguistic study of US Latinos are reviewed, with an emphasis on recent work in sociolinguistics. Predominant models of language contact are evaluated, as are factors contributing to variation. Among these factors are (a) the state of changes in progress; (b) the complexity of historical, socioeconomic, and demographic conditions of US Latinos; (c) the community's degree of contact with other ethnic/linguistic groups; (d) language attitudes toward the matrix and embedded languages; (e) the local evaluation and patterns of use of particular variants; and (f) the possibility of autochthonous innovation within the dialect. Questions of US Latino participation in changes beyond those in their immediate communities are addressed. The need to connect linguistic variation with other aspects of semiotic meaning is emphasized.
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    Annual Review of Anthropology 28 (1999), S. 455-478 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract Anthropologies of late modernity (also called postmodernity, postindustrial society, knowledge society, or information society) provide a number of stimulating challenges for all levels of social, cultural, and psychological theory, as well as for ethnographic and other genres of anthropological writing. Three key overlapping arenas of attention are the centrality of science and technology; decolonization, postcolonialism, and the reconstruction of societies after social trauma; and the role of the new electronic and visual media. The most important challenges of contemporary ethnographic practice include more than merely (a) the techniques of multilocale or multisited ethnography for strategically accessing different points in broadly spread processes, (b) the techniques of multivocal or multiaudience-addressed texts for mapping and acknowledging with greater precision the situatedness of knowledge, (c) the reworking of traditional notions of comparative work for a world that is increasingly aware of difference, and (d) acknowledging that anthropological representations are interventions within a stream of representations, mediations, and unequally inflected discourses competing for hegemonic control. Of equal importance are the challenges of juxtaposing, complementing, or supplementing other genres of writing, working with historians, literary theorists, media critics, novelists, investigative or in-depth journalists, writers of insider accounts (e.g. autobiographers, scientists writing for the public), photographers and film makers, and others.
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    Annual Review of Anthropology 28 (1999), S. 479-507 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract This review asks the question: What new avenues of social science enquiry are suggested by new ecological thinking, with its focus on nonequilibrium dynamics, spatial and temporal variation, complexity, and uncertainty? Following a review of the emergence of the "new ecology" and the highlighting of contrasts with earlier "balance of nature" perspectives, work emerging from ecological anthropology, political ecology, environmental and ecological economics, and debates about nature and culture are examined. With some important exceptions, much social science work and associated popular and policy debates remain firmly wedded to a static and equilibrial view. This review turns to three areas where a more dynamic perspective has emerged. Each has the potential to take central elements of new ecological thinking seriously, sometimes with major practical consequences for planning, intervention design, and management. First is the concern with spatial and temporal dynamics developed in detailed and situated analyses of "people in places," using, in particular, historical analysis as a way of explaining environmental change across time and space. Second is the growing understanding of environment as both the product of and the setting for human interactions, which link dynamic structural analyses of environmental processes with an appreciation of human agency in environmental transformation, as part of a "structuration" approach. Third is the appreciation of complexity and uncertainty in social-ecological systems and, with this, the recognition of that prediction, management, and control are unlikely, if not impossible.
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    Annual Review of Anthropology 28 (1999), S. 225-252 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Abstract The proposal that linguistic sounds such as phonemes, features, syllables, or tones can be meaningful, or sound-symbolic, contradicts the principles of arbitrariness and double articulation that are axiomatic to structural linguistics. Nevertheless, a considerable body of research that supports principles of sound symbolism has accumulated. This review discusses the most widely attested forms of sound symbolism and the research programs linked to sound symbolism that have influenced linguists and anthropologists most. Numerous reports of magnitude sound symbolism in the form of experimental studies and comparative surveys have been integrated into a biologically based theory of its motivation. Magnitude sound symbolism also catalyzed a number of experimental studies by psychologists and linguists in search of a universal sound-symbolic substrate underlying all languages. Although the search for a sound-symbolic substrate has been abandoned, the success rates of these studies have never been satisfactorily explained. Sound-symbolic processes have had a definitive impact on morphological analyses of phonesthemes and on historical linguists' understandings of diachronic processes. A typologically widespread form of sound symbolism occurs as a kind of lexical class known as the ideophone, which is conspicuously underdeveloped in standard average European languages, and highly perplexing for linguists and anthropologists. Although it has always been a respectable domain of inquiry in ethnopoetics and interpretive ethnography, the case for sound symbolism has of late been argued with renewed vigor on the part of psychological anthropologists and philosophers who see a paradigm shift under way.
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    Annual Review of Anthropology 28 (1999), S. i 
    ISSN: 0084-6570
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Ethnic Sciences , Biology
    Notes: Figure 1 Figure 1 A broad reflection on some of the major surprises to anthropological theory occasioned by the history, and in a number of instances the tenacity, of indigenous cultures in the twentieth century. We are not leaving the century with the same ideas that got us there. Contrary to the inherited notions of progressive development, whether of the political left or right, the surviving victims of imperial capitalism neither became all alike nor just like us. Contrary to the "despondency theory" of mid-century, the logical and historical precursor of dependency theory, surviving indigenous peoples aim to take cultural responsibility for what has been done to them. Across large parts of northern North America, even hunters and gatherers live, largely by hunting and gathering. The Eskimo are still there, and they are still Eskimo. Around the world the peoples give the lie to received theoretical oppositions between tradition and change, indigenous culture and modernity, townsmen and tribesmen, and other cliches of the received anthropological wisdom. Reports of the death of indigenous cultures-as of the demise of anthropology-have been exaggerated.
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 231-285 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract Deepwater formation, the process whereby surface water is actively converted into deep water through heat and freshwater exchange at the air-sea interface, is known to occur in the North Atlantic but not in the North Pacific. As such, the thermohaline circulation is fundamentally different in these two regions. In this review we provide a description of this circulation and outline a number of reasons as to why deep water is formed in the North Atlantic but not in the North Pacific. Special emphasis is given to the role of interactions with the Arctic Ocean. We extend our analysis to discuss the observational evidence and current theories for decadal-interdecadal climate variability in each region, with particular focus on the role of the ocean. Differences between the North Atlantic and North Pacific are highlighted.
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 287-312 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract The region of the solar system immediately beyond Neptune's orbit is densely populated with small bodies. This region, known as the Kuiper Belt, consists of objects that may predate Neptune, the orbits of which provide a fossil record of processes operative in the young solar system. The Kuiper Belt contains some of the Solar System's most primitive, least thermally processed matter. It is probably the source of the short-period comets and Centaurs, and may also supply collisionally generated interplanetary dust. I discuss the properties of the Kuiper Belt and provide an overview of the outstanding scientific issues.
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    Annual Review of Earth and Planetary Sciences 27 (1999), S. 385-415 
    ISSN: 0084-6597
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Geosciences , Physics
    Notes: Abstract The detailed morphology of impact craters is now believed to be mainly caused by the collapse of a geometrically simple, bowl-shaped "transient crater." The transient crater forms immediately after the impact. In small craters, those less than approximately 15 km diameter on the Moon, the steepest part of the rim collapses into the crater bowl to produce a lens of broken rock in an otherwise unmodified transient crater. Such craters are called "simple" and have a depth-to-diameter ratio near 1:5. Large craters collapse more spectacularly, giving rise to central peaks, wall terraces, and internal rings in still larger craters. These are called "complex" craters. The transition between simple and complex craters depends on 1/g, suggesting that the collapse occurs when a strength threshold is exceeded. The apparent strength, however, is very low: only a few bars, and with little or no internal friction. This behavior requires a mechanism for temporary strength degradation in the rocks surrounding the impact site. Several models for this process, including acoustic fluidization and shock weakening, have been considered by recent investigations. Acoustic fluidization, in particular, appears to produce results in good agreement with observations, although better understanding is still needed.
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    Annual Review of Neuroscience 22 (1999), S. 1-10 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract FM1-43 and similar styryl dyes have proven useful as probes for membrane trafficking because they reversibly stain membranes, are impermeable to membranes, and are more fluorescent when bound to membranes than when in solution. Because these dyes stain membranes in an activity-dependent manner, they are ideal for studies of neurotransmitter release mechanisms such as synaptic vesicle recycling, exocytosis, and endocytosis. FM dyes have been used in conjunction with other techniques such as fluorescent calcium indicator dyes and electrophysiological techniques to elucidate mechanisms of presynaptic calcium homeostasis and modulation of neurotransmitter release. Presynaptic membranes have been marked by FM dyes in studies of synaptogenesis and reinnervation. As a probe for endocytosed membranes, these dyes have been used to examine vacuole formation in yeast. These versatile membrane dyes are useful in a variety of applications.
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    Annual Review of Neuroscience 22 (1999), S. 29-47 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Many pathways in the developing visual system are restructured and become highly organized even before vision occurs. Yet the developmental processes underlying the remodeling of visual connectivity are crucially dependent on retinal activity. Surprisingly, the immature and light-insensitive retina spontaneously generates a pattern of rhythmic bursting activity during the period when the connectivity patterns of retinal ganglion cells are shaped. Spatially, the activity is seen to spread across the retina in the form of waves that bring into synchrony the bursts of neighboring cells. Waves are present in the developing retina of higher and lower vertebrates, which suggests that this form of activity may be a common and fundamental mechanism employed in the activity-dependent refinement of early patterns of visual connections. Unraveling the cues encoded by the waves promises to provide important insights into how interactions driven by specific patterns of activity could lead to the modification of connectivity during development.
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    Annual Review of Neuroscience 22 (1999), S. 175-195 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Over the past three decades, compelling evidence has emerged that the immune system can attack the nervous system with devastating consequences for human health. Either cell-mediated or humoral (antibody-mediated) autoimmune mechanisms may predominate in effecting a given disease, and either glia or neurons may fall under immune attack. A subset of these diseases has been particularly useful for understanding fundamental neuroscience as well as mechanisms of human disease. This subset involves humoral autoimmune attack on cell surface molecules subserving transmembrane signaling of excitable cells; special emphasis is placed here on proteins involved in synaptic transmission. We begin by reviewing the prototypic humoral autoimmune disease of synaptic transmission, myasthenia gravis. This provides a context for insights obtained from the study of diseases targeting molecules that regulate synaptic transmission at the neuromuscular junction and in the central nervous system. We also explore a disease where autoimmunity produces agonist antibodies acting at two distinct G-protein-coupled receptors. We conclude with an exploration of the vital issue of access of antibodies to targets within the central nervous system and the implications that such access may have in the pathogenesis of poorly understood idiopathic central nervous system diseases.
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    Annual Review of Neuroscience 22 (1999), S. 295-318 
    ISSN: 0147-006X
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Despite considerable evidence that neuronal activity influences the organization and function of circuits in the developing and adult brain, the molecular signals that translate activity into structural and functional changes in connections remain largely obscure. This review discusses the evidence implicating neurotrophins as molecular mediators of synaptic and morphological plasticity. Neurotrophins are attractive candidates for these roles because they and their receptors are expressed in areas of the brain that undergo plasticity, activity can regulate their levels and secretion, and they regulate both synaptic transmission and neuronal growth. Although numerous experiments show demonstrable effects of neurotrophins on synaptic plasticity, the rules and mechanisms by which they exert their effects remain intriguingly elusive.
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    Annual Review of Immunology 17 (1999), S. 283-295 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The transmembrane receptor Notch participates in diverse cell fate decisions throughout embryonic development. Notch receptors and their ligands are expressed in the mammalian thymus, raising the possibility that Notch could regulate T cell fate decisions. Expression of a constitutively activated form of Notch in developing thymocytes causes thymocytes normally destined for the CD4 lineage to adopt the CD8 lineage instead. This suggests that Notch activity normally acts to direct CD4+CD8+ precursors to the CD8 lineage. The choice between CD4 and CD8 T cell fates is also controlled by MHC recognition during positive selection, implying that recognition of class I or II MHC might regulate Notch signaling. Possible models for the regulation of Notch by MHC recognition during CD4 versus CD8 lineage determination are discussed.
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    Annual Review of Immunology 17 (1999), S. 399-433 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The secondary lymphoid tissues are located at strategic sites where foreign antigens can be efficiently brought together with immune system regulatory and effector cells. The organized structure of the secondary lymphoid tissues is thought to enhance the sensitivity of antigen recognition and to support proper regulation of the activation and maturation of the antigen-responsive lymphoid cells. Although a substantial amount is known about the cellular elements that compose the lymphoid and nonlymphoid components of the secondary lymphoid tissues, information concerning the signals that control the development of the tissues and that maintain the organized tissue microenvironment remain undefined. Studies over the past few years have identified lymphotoxin as a critical signaling molecule not only for the organogenesis of secondary lymphoid tissues but for the maintenance of aspects of their microarchitecture as well. Additional signaling molecules that contribute to the formation of normal lymphoid tissue structure are being identified at an accelerating pace. Analyses of mouse strains with congenital defects in different aspects of secondary lymphoid tissue development are beginning to clarify the role of these tissues in immune responses and host defense. This review focuses on studies defining recently identified crucial signals for the biogenesis of secondary lymphoid organs and for the maintenance of their proper microarchitecture. It also discusses new insights into how the structure of these tissues supports effective immune responses.
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    Annual Review of Immunology 17 (1999), S. 523-554 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The two major subsets of T lymphocytes in the peripheral immune system, the helper and cytotoxic T cells, are defined by their expression of either the CD4 or the CD8 glycoproteins, respectively. Expression of these molecules, which serve as coreceptors by interacting specifically with either MHC class II or class I molecules, also defines discrete stages of T cell development within the thymus. Thus, CD4+ and CD8+ single-positive (SP) thymocytes arise from common progenitor double positive (DP) cells that express both CD4 and CD8, during a process known as positive selection. The molecular mechanisms underlying the developmental choice toward the helper or cytotoxic lineage remain poorly understood. Because regulation of coreceptor gene expression appears to be coupled to the phenotypic choice of the differentiating T cell, it is likely that shared signaling pathways direct CD4 and CD8 transcription and the development of an uncommited DP thymocyte toward either the helper or cytotoxic lineage. Therefore, an understanding of how CD4 and CD8 expression is regulated will not only provide insights into transcriptional control mechanisms in T cells, but may also result in the identification of molecular factors that are involved in lineage choices during T cell development. In this review, we summarize recent progress that has been made toward an understanding of how CD4 and CD8 gene expression is regulated.
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    Annual Review of Immunology 17 (1999), S. 657-700 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract In addition to CD4, the human immunodeficiency virus (HIV) requires a coreceptor for entry into target cells. The chemokine receptors CXCR4 and CCR5, members of the G protein-coupled receptor superfamily, have been identified as the principal coreceptors for T cell line-tropic and macrophage-tropic HIV-1 isolates, respectively. The updated coreceptor repertoire includes numerous members, mostly chemokine receptors and related orphans. These discoveries provide a new framework for understanding critical features of the basic biology of HIV-1, including the selective tropism of individual viral variants for different CD4+ target cells and the membrane fusion mechanism governing virus entry. The coreceptors also provide molecular perspectives on central puzzles of HIV-1 disease, including the selective transmission of macrophage-tropic variants, the appearance of T cell line-tropic variants in many infected persons during progression to AIDS, and differing susceptibilities of individuals to infection and disease progression. Genetic findings have yielded major insights into the in vivo roles of individual coreceptors and their ligands; of particular importance is the discovery of an inactivating mutation in the CCR5 gene which, in homozygous form, confers strong resistance to HIV-1 infection. Beyond providing new perspectives on fundamental aspects of HIV-1 transmission and pathogenesis, the coreceptors suggest new avenues for developing novel therapeutic and preventative strategies to combat the AIDS epidemic.
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    Annual Review of Immunology 17 (1999), S. 875-904 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Major histocompatibility complex class I-specific inhibitory receptors on natural killer cells prevent the lysis of healthy autologous cells. The outcome of this negative signal is not anergy or apoptosis of natural killer cells but a transient abortion of activation signals. The natural killer inhibitory receptors fulfill this function by recruiting the tyrosine phosphatase SHP-1 through a cytoplasmic immunoreceptor tyrosine-based inhibition motif. This immunoreceptor tyrosine-based inhibition motif has become the hallmark of a growing family of receptors with inhibitory potential, which are expressed in various cell types such as monocytes, macrophages, dendritic cells, leukocytes, and mast cells. Most of the natural killer inhibitory receptors and two members of a monocyte inhibitory-receptor family bind major histocompatibility complex class I molecules. Ligands for many of the other receptors have yet to be identified. The inhibitory-receptor superfamily appears to regulate many types of immune responses by blocking cellular activation signals.
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    Annual Review of Immunology 17 (1999), S. 435-466 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Superantigens (SAGs) are a class of immunostimulatory and disease-causing proteins of bacterial or viral origin with the ability to activate large fractions (5-20%) of the T cell population. Activation requires simultaneous interaction of the SAG with the Vbeta domain of the T cell receptor (TCR) and with major histocompatibility complex (MHC) class II molecules on the surface of an antigen-presenting cell. Recent advances in knowledge of the three-dimensional structure of bacterial SAGs, and of their complexes with MHC class II molecules and the TCR beta chain, provide a framework for understanding the molecular basis of T cell activation by these potent mitogens. These structures along with those of TCR-peptide/MHC complexes reveal how SAGs circumvent the normal mechanism for T cell activation by peptide/MHC and how they stimulate T cells expressing TCR beta chains from a number of different families, resulting in polyclonal T cell activation. The crystal structures also provide insights into the basis for the specificity of different SAGs for particular TCR beta chains, and for the observed influence of the TCR alpha chain on SAG reactivity. These studies open the way to the design of SAG variants with altered binding properties for TCR and MHC for use as tools in dissecting structure-activity relationships in this system.
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    Annual Review of Immunology 17 (1999), S. 369-397 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Exciting breakthroughs in the last two years have begun to elucidate the structural basis of cellular immune recognition. Crystal structures have been determined for full-length and truncated forms of alphabeta T cell receptor (TCR) heterodimers, both alone and in complex with their peptide-MHC (pMHC) ligands or with anti-TCR antibodies. In addition, a truncated CD8 coreceptor has been visualized with a pMHC. Aided in large part by the substantial body of knowledge accumulated over the last 25 years on antibody structure, a number of general conclusions about TCR structure and its recognition of antigen can already be derived from the relatively few TCR structures that have been determined. Small, but important, variations between TCR and antibody structures bear on their functional differences as well as on their specific antigen recognition requirements. As observed in antibodies, canonical CDR loop structures are already emerging for some of the TCR CDR loops. Highly similar docking orientations of the TCR Valpha domains in the TCR/pMHC complex appear to play a primary role in dictating orientation, but the Vbeta positions diverge widely. Similar TCR contact positions, but whose exact amino acid content can vary, coupled with relatively poor interface shape complementarity, may explain the flexibility and short half-lives of many TCR interactions with pMHC. Here we summarize the current state of this field, and suggest that the knowledge gap between the three-dimensional structure and the signaling function of the TCR can be bridged through a synthesis of molecular biological and biophysical techniques.
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    Annual Review of Immunology 17 (1999), S. 467-522 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract T cells constantly sample their environment using receptors (TCR) that possess both a germline-encoded low affinity for major histocompatibility complex (MHC) molecules and a highly diverse set of CDR3 regions contributing to a range of affinities for specific peptides bound to these MHC molecules. The decision of a T cell "to sense and to respond" with proliferation and effector activity rather than "to sense, live on, but not respond" is dependent on TCR interaction with a low number of specific foreign peptide:MHC molecule complexes recognized simultaneously with abundant self peptide-containing complexes. Interaction with self-complexes alone, on the other hand, generates a signal for survival without a full activation response. Current models for how this distinction is achieved are largely based on translating differences in receptor affinity for foreign versus self ligands into intracellular signals that differ in quality, intensity, and/or duration. A variety of rate-dependent mechanisms involving assembly of molecular oligomers and enzymatic modification of proteins underlie this differential signaling. Recent advances have been made in measuring TCR:ligand interactions, in understanding the biochemical origin of distinct proximal and distal signaling events resulting from TCR binding to various ligands, and in appreciating the role of feedback pathways. This new information can be synthesized into a model of how self and foreign ligand recognition each evoke the proper responses from T cells, how these two classes of signaling events interact, and how pathologic responses may arise as a result of the underlying properties of the system. The principles of signal spreading and stochastic resonance incorporated into this model reveal a striking similarity in mechanisms of decision-making among T cells, neurons, and bacteria.
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    Annual Review of Immunology 17 (1999), S. 625-656 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Human immunodeficiency virus-1 (HIV-1) is usually transmitted through sexual contact and in the very early stages of infection establishes a persistent infection in lymphatic tissues (LT). Virus is produced and stored at this site in a dynamic process that slowly depletes the immune system of CD4+ T cells, setting the stage for AIDS. In this review, I describe the changes in viral and CD4+ T cell populations in LT over the course of infection and after treatment. I present recent evidence that productively infected CD4+ T cells play an important role in establishing persistent infection from the onset, and that the LT are the major reservoir where virus is produced and stored on follicular dendritic cells (FDCs). I discuss the methods used to define the size of viral and CD4+ T cell populations in LT and the nature of virus-host cell interactions in vivo. These experimental approaches have identified populations of latently and chronically infected cells in which virus can elude host defenses, perpetuate infection, and escape eradication by highly active antiretroviral treatment (HAART). I discuss the dramatic impact of HAART on suppressing virus production, reducing the pool of stored virus, and restoring CD4+ T cell populations. I discuss the contributions of thymopoiesis and other renewal mechanisms, lymphatic homeostasis and trafficking to these changes in CD4+ T cell populations in LT, and conclude with a model of immune depletion and repopulation based on the limited regenerative capacity of the adult and the uncompensated losses of productively infected cells that treatment stems. The prediction of this model is that immune regeneration will be slow, variable, and partial. It is nonetheless encouraging to know that even in late stages of infection, control of active replication of HIV-1 provides an opportunity for the immune system to recover from the injuries inflicted by infection.
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    Annual Review of Immunology 17 (1999), S. 829-874 
    ISSN: 0732-0582
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Advances in gene technology have allowed the manipulation of molecular interactions that shape the T cell repertoire. Although recognized as fundamental aspects of T lymphocyte development, only recently have the mechanisms governing positive and negative selection been examined at a molecular level. Positive selection refers to the active process of rescuing MHC-restricted thymocytes from programmed cell death. Negative selection refers to the deletion or inactivation of potentially autoreactive thymocytes. This review focuses on interactions during thymocyte maturation that define the T cell repertoire, with an emphasis placed on current literature within this field.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 1-25 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 97-131 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract The first plant protein kinase sequences were reported as recently as 1989, but by mid-1998 there were more than 500, including 175 in Arabidopsis thaliana alone. Despite this impressive pace of discovery, progress in understanding the detailed functions of protein kinases in plants has been slower. Protein serine/threonine kinases from A. thaliana can be divided into around a dozen major groups based on their sequence relationships. For each of these groups, studies on animal and fungal homologs are briefly reviewed, and direct studies of their physiological functions in plants are then discussed in more detail. The network of protein-serine/threonine kinases in plant cells appears to act as a "central processor unit" (cpu), accepting input information from receptors that sense environmental conditions, phytohormones, and other external factors, and converting it into appropriate outputs such as changes in metabolism, gene expression, and cell growth and division.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 447-472 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract This review discusses how the pressure probe has evolved from an instrument for measuring cell turgor and other water relations parameters into a device for sampling the contents of individual higher plant cells in situ in the living plant. Together with a suite of microanalytical techniques it has permitted the mapping of water and solute relations at the resolution of single cells and has the potential to link quantitatively the traditionally separate areas of water relations and metabolism. The development of the probe is outlined and its modification to measure root pressure and xylem tension described. The deployment of the pressure probe to determine and map turgor, hydraulic conductivity, reflection coefficient, cell rheological properties, solute concentrations and enzyme activities at the resolution of single cells is discussed. The controversy surrounding the interpretation of results obtained with the xylem-pressure probe is included. Possible further developments of the probe and applications of single cell sampling are suggested.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 601-639 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Photoreduction of dioxygen in photosystem I (PSI) of chloroplasts generates superoxide radicals as the primary product. In intact chloroplasts, the superoxide and the hydrogen peroxide produced via the disproportionation of superoxide are so rapidly scavenged at the site of their generation that the active oxygens do not inactivate the PSI complex, the stromal enzymes, or the scavenging system itself. The overall reaction for scavenging of active oxygens is the photoreduction of dioxygen to water via superoxide and hydrogen peroxide in PSI by the electrons derived from water in PSII, and the water-water cycle is proposed for these sequences. An overview is given of the molecular mechanism of the water-water cycle and microcompartmentalization of the enzymes participating in it. Whenever the water-water cycle operates properly for scavenging of active oxygens in chloroplasts, it also effectively dissipates excess excitation energy under environmental stress. The dual functions of the water-water cycle for protection from photoinihibition are discussed.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 505-537 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Asymmetric cell divisions generate cells with different fates. In plants, where cells do not move relative to another cell, the specification and orientation of these divisions is an important mechanism to generate the overall cellular pattern during development. This review summarizes our knowledge of selected cases of asymmetric cell division in plants, in the context of recent insights into mechanisms underlying this process in bacteria, algae, yeast, and animals.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 571-599 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Many plants increase in freezing tolerance upon exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. In this review, recent advances in determining the nature and function of genes with roles in freezing tolerance and the mechanisms involved in low temperature gene regulation and signal transduction are described. One of the important conclusions to emerge from these studies is that cold acclimation includes the expression of certain cold-induced genes that function to stabilize membranes against freeze-induced injury. In addition, a family of Arabidopsis transcription factors, the CBF/DREB1 proteins, have been identified that control the expression of a regulon of cold-induced genes that increase plant freezing tolerance. These results along with many of the others summarized here further our understanding of the basic mechanisms that plants have evolved to survive freezing temperatures. In addition, the findings have potential practical applications as freezing temperatures are a major factor limiting the geographical locations suitable for growing crop and horticultural plants and periodically account for significant losses in plant productivity.
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    Annual Review of Plant Physiology and Plant Molecular Biology 50 (1999), S. 665-693 
    ISSN: 1040-2519
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Phosphorus is one of the major plant nutrients that is least available in the soil. Consequently, plants have developed numerous morphological, physiological, biochemical, and molecular adaptations to acquire phosphate (Pi). Enhanced ability to acquire Pi and altered gene expression are the hallmarks of plant adaptation to Pi deficiency. The intricate mechanisms involved in maintaining Pi homeostasis reflect the complexity of Pi acquisition and translocation in plants. Recent discoveries of multiple Pi transporters have opened up opportunities to study the molecular basis of Pi acquisition by plants. An increasing number of genes are now known to be activated under Pi starvation. Some of these genes may be involved in Pi acquisition, transfer, and signal transduction during Pi stress. This review provides an overview of plant adaptations leading to enhanced Pi acquisition, with special emphasis on recent developments in the molecular biology of Pi acquisition.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 113-140 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Cell proliferation and cell death must be closely regulated to maintain the integrity of the immune system during the lifetime of multicellular organisms. Proliferative expansion of lymphoid cells is required for effective immune responses against invading microorganisms. However, following infection eradication, expanded effector cells must be eliminated to prevent non-adaptive accumulation of cells. Therefore, higher vertebrates have developed an extensive network of signal transduction pathways that allow integration of cell survival and cell death stimuli. This network functions to ensure the controlled activation and expansion of cells during an immune response and the deletion of lymphoid cells that are no longer needed at the end of an immune response. Extracellular signals appear to control both mechanisms. Ultimate responses are integrated through cell surface receptors that are linked to intracellular signaling cascades. These signal transduction pathways converge to regulate cell fate at both transcriptional and post-transcriptional levels. In this review, the role of pathways triggered by TNFR-related molecules that determine the fate of lymphoid cells during development and activation is summarized.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 185-230 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Ubiquitous among eukaryotes, the ADF/cofilins are essential proteins responsible for the high turnover rates of actin filaments in vivo. In vertebrates, ADF and cofilin are products of different genes. Both bind to F-actin cooperatively and induce a twist in the actin filament that results in the loss of the phalloidin-binding site. This conformational change may be responsible for the enhancement of the off rate of subunits at the minus end of ADF/cofilin-decorated filaments and for the weak filament-severing activity. Binding of ADF/cofilin is competitive with tropomyosin. Other regulatory mechanisms in animal cells include binding of phosphoinositides, phosphorylation by LIM kinases on a single serine, and changes in pH. Although vertebrate ADF/cofilins contain a nuclear localization sequence, they are usually concentrated in regions containing dynamic actin pools, such as the leading edge of migrating cells and neuronal growth cones. ADF/cofilins are essential for cytokinesis, phagocytosis, fluid phase endocytosis, and other cellular processes dependent upon actin dynamics.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 341-363 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Actin-related proteins (Arps) participate in a diverse array of cellular processes. They modulate assembly of conventional actin, contribute to microtubule-based motility catalyzed by dynein, and serve as integral components of large protein complexes required for gene expression. We highlight here recent work aimed at understanding the roles played by Arps in each of these processes.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 63-80 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Organelle transport has been proposed to proceed in two steps: long-range transport along microtubules and local delivery via actin filaments. This model is supported by recent studies of pigment transport in several cell types and transport in neurons, and in several cases, class V myosin has been implicated as the actin-based motor. Mutations in mice (dilute) and yeast (myo2) have also implicated this class of myosin in organelle transport, and genetic interactions in yeast have indicated that a kinesin-related protein (Smy1p) plays a supporting role. This link between members of two different motor superfamilies has now taken a surprising turn: There is evidence for a physical interaction between class V myosins and kinesin or Smy1p in both mice and yeast.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 141-183 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Proteins of the kinesin superfamily utilize a conserved catalytic motor domain to generate movements in a wide variety of cellular processes. In this review, we discuss the rapid expansion in our understanding of how eukaryotic cells take advantage of these proteins to generate force and movement in diverse functional contexts. We summarize several recent examples revealing that the simplest view of a kinesin motor protein binding to and translocating a cargo along a microtubule track is inadequate. In fact, this paradigm captures only a small subset of the many ways in which cells harness force production to the generation of intracellular movements and functions. We also highlight several situations where the catalytic kinesin motor domain may not be used to generate movement, but instead may be used in other biochemical and functional contexts. Finally, we review some recent ideas about kinesin motor regulation, redundancy, and cargo attachment strategies.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 269-290 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Caspase activation plays a central role in the execution of apoptosis. The key components of the biochemical pathways of caspase activation have been recently elucidated. In this review, we focus on the two most well-studied pathways of caspase activation: the cell surface death receptor pathway and the mitochondria-initiated pathway. In the cell surface death receptor pathway, activation of caspase-8 following its recruitment to the death-inducing signaling complex (DISC) is the critical event that transmits the death signal. This event is regulated at several different levels by various viral and mammalian proteins. Activated caspase-8 can activate downstream caspases by direct cleavage or indirectly by cleaving Bid and inducing cytochrome c release from the mitochondria. In the mitochondrial-initiated pathway, caspase activation is triggered by the formation of a multimeric Apaf-1/cytochrome c complex that is fully functional in recruiting and activating procaspase-9. Activated caspase-9 will then cleave and activate downstream caspases such as caspase-3, -6, and -7. This pathway is regulated at several steps, including the release of cytochrome c from the mitochondria, the binding and hydrolysis of dATP/ATP by Apaf-1, and the inhibition of caspase activation by the proteins that belong to the inhibitors of apoptosis (IAP).
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 365-391 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract Subcellular asymmetry, cell polarity, is fundamental to the diverse specialized functions of eukaryotic cells. In yeast, cell polarization is essential to division and mating. As a result, this highly accessible experimental system serves as a paradigm for deciphering the molecular mechanisms underlying the generation of polarity. Beyond yeast, cell polarity is essential to the partitioning of cell fate in embryonic development, the generation of axons and their guidance during neuronal development, and the intimate communication between lymphocytes within the immune system. The polarization of yeast cells shares many features with that of these more complex examples, including regulation by both intrinsic and extrinsic cues, conserved regulatory molecules such as Cdc42 GTPase, and asymmetry of the cytoskeleton as its centerpiece. This review summarizes the molecular pathways governing the generation of cell polarity in yeast.
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    Annual Review of Cell and Developmental Biology 15 (1999), S. 411-433 
    ISSN: 1081-0706
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology , Medicine
    Notes: Abstract The formation of the vertebrate nervous system is initiated at gastrula stages of development, when signals from a specialized cluster of cells (the organizer) trigger neural development in the ectoderm. This process, termed neural induction, was first described in 1924 and stemmed from experiments on amphibia (Spemann & Mangold 1924). In recent years, the molecular mechanisms underlying neural induction in the amphibian have been elucidated. Surprisingly, neuralizing agents secreted by the organizer do not act via receptor-mediated signaling events; rather, these factors antagonize local epidermal inducers within the cells of the dorsal ectoderm and function to uncover the latent neural fate of these cells. Many of the recent advances in our understanding of vertebrate neural induction come from studies on the frog, Xenopus laevis. It is now clear that a blockade of signaling of the bone morphogenetic proteins (BMPs) during gastrula stages is sufficient to initiate neuralization of the ectoderm in this species. Thus this review first details our current understanding of neural induction, using the amphibian as a model. We then use data emerging from other systems to examine the extent to which the Xenopus studies can be applied to other vertebrate species. The initiation of the neurectoderm-specific gene expression program and subsequent steps in patterning and neuronal development are only touched on here. We focus primarily on the initial establishment of the neural fate in the vertebrate gastrula ectoderm.
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    Annual Review of Biochemistry 68 (1999), S. 687-728 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract X-ray crystallography shows the myosin cross-bridge to exist in two conformations, the beginning and end of the "power stroke." A long lever-arm undergoes a 60o to 70o rotation between the two states. This rotation is coupled with changes in the active site (OPEN to CLOSED) and phosphate release. Actin binding mediates the transition from CLOSED to OPEN. Kinetics shows that the binding of myosin to actin is a two-step process which affects ATP and ADP affinity. The structural basis of these effects is not explained by the presently known conformers of myosin. Therefore, other states of the myosin cross-bridge must exist. Moreover, cryoelectronmicroscopy has revealed other angles of the cross-bridge lever arm induced by ADP binding. These structural states are presently being characterized by site-directed mutagenesis coupled with kinetic analysis.
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    Annual Review of Biochemistry 68 (1999), S. 863-911 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract Membrane fusion involves the merger of two phospholipid bilayers in an aqueous environment. In artificial lipid bilayers, fusion proceeds by means of defined transition states, including hourglass-shaped intermediates in which the proximal leaflets of the fusing membranes are merged whereas the distal leaflets are separate (fusion stalk), followed by the reversible opening of small aqueous fusion pores. Fusion of biological membranes requires the action of specific fusion proteins. Best understood are the viral fusion proteins that are responsible for merging the viral with the host cell membrane during infection. These proteins undergo spontaneous and dramatic conformational changes upon activation. In the case of the paradigmatic fusion proteins of the influenza virus and of the human immunodeficiency virus, an amphiphilic fusion peptide is inserted into the target membrane. The protein then reorients itself, thus forcing the fusing membranes together and inducing lipid mixing. Fusion of intracellular membranes in eukaryotic cells involves several protein families including SNAREs, Rab proteins, and Sec1/Munc-18 related proteins (SM-proteins). SNAREs form a novel superfamily of small and mostly membrane-anchored proteins that share a common motif of about 60 amino acids (SNARE motif). SNAREs reversibly assemble into tightly packed helical bundles, the core complexes. Assembly is thought to pull the fusing membranes closely together, thus inducing fusion. SM-proteins comprise a family of soluble proteins that bind to certain types of SNAREs and prevent the formation of core complexes. Rab proteins are GTPases that undergo highly regulated GTP-GDP cycles. In their GTP form, they interact with specific proteins, the effector proteins. Recent evidence suggests that Rab proteins function in the initial membrane contact connecting the fusing membranes but are not involved in the fusion reaction itself.
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    Annual Review of Biochemistry 68 (1999), S. 459-486 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract Members of the Rho family of small Ras-like GTPases-including RhoA, -B, and -C, Rac1 and -2, and Cdc42-exhibit guanine nucleotide-binding activity and function as molecular switches, cycling between an inactive GDP-bound state and an active GTP-bound state. The Rho family GTPases participate in regulation of the actin cytoskeleton and cell adhesion through specific targets. Identification and characterization of these targets have begun to clarify how the Rho family GTPases act to regulate cytoskeletal structure and cell-cell and cell-substratum contacts in mammalian cells. The Rho family GTPases are also involved in regulation of smooth muscle contraction, cell morphology, cell motility, neurite retraction, and cytokinesis. However, the molecular mechanisms by which the Rho family GTPases participate in the regulation of such processes are not well established.
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    Annual Review of Biochemistry 68 (1999), S. 559-581 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract The determination of several structures of nuclear receptor ligand binding domains (LBD) has led to new insights into the mechanism of action of this very important class of receptors. This review describes and compares the different LBD structures and their relationship to the function of the nuclear receptors. The role of the ligand in the LBD structures and the implications of ligand structure on receptor activity are also discussed. Structural information regarding interactions between the LBD and coactivator proteins and the potential role of these interactions in ligand agonism and antagonism is reviewed. Different pathways for nuclear receptor signaling and the use of new ligands to investigate these pathways are also described.
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    Annual Review of Biochemistry 68 (1999), S. 523-558 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract Risk for cardiovascular disease due to atherosclerosis increases with increasing concentrations of low-density lipoprotein (LDL) cholesterol and is inversely proportional to the levels of high-density lipoprotein (HDL) cholesterol. The receptor-mediated control of plasma LDL levels has been well understood for over two decades and has been a focus for the pharmacologic treatment of hypercholesterolemia. In contrast, the first identification and characterization of a receptor that mediates cellular metabolism of HDL was only recently reported. This receptor, called scavenger receptor class B type I (SR-BI), is a fatty acylated glycoprotein that can cluster in caveolae-like domains on the surfaces of cultured cells. SR-BI mediates selective lipid uptake from HDL to cells. The mechanism of selective lipid uptake is fundamentally different from that of classic receptor-mediated endocytic uptake via coated pits and vesicles (e.g. the LDL receptor pathway) in that it involves efficient receptor-mediated transfer of the lipids, but not the outer shell proteins, from HDL to cells. In mice, SR-BI plays a key role in determining the levels of plasma HDL cholesterol and in mediating the regulated, selective delivery of HDL-cholesterol to steroidogenic tissues and the liver. Significant alterations in SR-BI expression can result in cardiovascular and reproductive disorders. SR-BI may play a similar role in humans; thus, modulation of its activity may provide the basis of future approaches to the treatment and prevention of atherosclerotic disease.
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    Annual Review of Biochemistry 68 (1999), S. 779-819 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract De novo protein design has recently emerged as an attractive approach for studying the structure and function of proteins. This approach critically tests our understanding of the principles of protein folding; only in de novo design must one truly confront the issue of how to specify a protein's fold and function. If we truly understand proteins, it should be possible to design receptors, enzymes, and ion channels from scratch. Further, as this understanding evolves and is further refined, it should be possible to design proteins and biomimetic polymers with properties unprecedented in nature.
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    Annual Review of Biochemistry 68 (1999), S. 965-1014 
    ISSN: 0066-4154
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Chemistry and Pharmacology , Biology
    Notes: Abstract The protein kinase Akt/PKB is activated via a multistep process by a variety of signals. In the early steps of this process, PI-3 kinase-generated D3-phosphorylated phosphoinositides bind the Akt PH domain and induce the translocation of the kinase to the plasma membrane where it co-localizes with phosphoinositide-dependent kinase-1. By binding to the PH domains of both Akt and phosphoinositide-dependent kinase-1, D3-phosphorylated phosphoinositides appear to also induce conformational changes that permit phosphoinositide-dependent kinase-1 to phosphorylate the activation loop of Akt. The paradigm of Akt activation via phosphoinositide-dependent phosphorylation provided a framework for research into the mechanism of activation of other members of the AGC kinase group (p70S6K, PKC, and PKA) and members of the Tec tyrosine kinase family (TecI, TecII, Btk/Atk, Itk/Tsk/Emt, Txk/Rlk, and Bm/Etk). The result was the discovery that these kinases and Akt are activated by overlapping pathways. In this review, we present our current understanding of the regulation and function of the Akt kinase and we discuss the common and unique features of the activation processes of Akt and the AGC and Tec kinase families. In addition, we present an overview of the biosynthesis of phosphoinositides that contribute to the regulation of these kinases.
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    Annual Review of Entomology 44 (1999), S. 483-505 
    ISSN: 0066-4170
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract This investigation into the natural history and behavior of 81 species of cerambycid beetles suggests that reproductive behavior is correlated with the condition of the larval host: Adults of species whose larvae attack living trees tend to show behavioral differences from those that attack dying or dead hosts. Behavioral differences among species that are associated with larval host condition include: (a) choice of adult food source and whether adults feed at all; (b) mechanisms of mate location and the role of long-range pheromones; (c) vagility and dispersal behaviors of adults; (d) location of the mating site; and (e) duration of copulation.
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    Annual Review of Entomology 44 (1999), S. 429-455 
    ISSN: 0066-4170
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Notes: Abstract Examination of the function, chemistry, and pharmacology of the voltage-gated insect sodium channel (ISC) reveals that the ISC closely resembles its vertebrate counterpart in electrophysiology and ion conductance, primary structure and allocation of all functional domains, and its pharmacological diversity and flexibility exhibited by the occurrence of different allosterically coupled receptor-binding sites for various neurotoxicants. The toxicants include several groups of insecticides, namely DDT and its analogues, pyrethroids, N-alkylamides, and dihydropyrazoles, which affect channel gating and ion permeability. Despite their similarity, the insect and vertebrate channels are pharmacologically distinguishable, as revealed by the responsiveness of the heterologously expressed Drosophila para clone to channel modifiers and blockers and the occurrence of the insect-selective sodium channel neurotoxins derived from arachnid venoms presently used for the design of recombinant baculovirus-mediated selective bioinsecticides. The pharmacological specificity of the ISC may lead to the design of insect-selective toxicants, and its pharmacological flexibility may direct the use of ISC insecticides for resistance management. Insecticide resistance [such as knockdown resistance (KDR)] is acquired by natural selection and operated by increased metabolism, channel mutagenesis, or both. The resistance issue can be dealt with in several ways. One is by simultaneous application of low doses of synergistic, allosterically coupled mixtures (thus delaying or preventing the onset of resistance). An alternative is to replace an insecticide to which resistance was acquired by channel mutation with a different ISC toxicant to which increased susceptibility was conferred by the same mutation. Such a possibility was exemplified by a significant increase in susceptibility to N-alkylamides, as well as an insect-selective neurotoxin revealed by KDR insects. Third, both of these methods can be combined. Thus owing to its pharmacological uniqueness, the ISC may serve as a high-priority target for future selective and resistance-manageable insecticides.
    Type of Medium: Electronic Resource
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