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  • Chemistry  (114,948)
  • General Chemistry  (18,165)
  • Cell & Developmental Biology  (7,340)
  • 1995-1999  (40,962)
  • 1980-1984  (36,387)
  • 1975-1979  (30,904)
  • 1955-1959  (14,035)
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  • 1
    Electronic Resource
    Electronic Resource
    Springer
    Journal of molecular evolution 15 (1980), S. 79-101 
    ISSN: 1432-1432
    Keywords: Molecules ; Interstellar ; Chemistry ; Isotopes ; Solar system
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The study of interstellar molecules broadly includes two areas of interest. One area uses the unique ability of molecules to act as probes of the physical conditions in the cold, dense, visually opaque component of the interstellar medium. The physical properties of this and other components of the interstellar medium are summarized. The other area deals with the chemistry of interstellar molecules, recent aspects of which are emphasized in this review. Gas-phase chemistry, shock chemistry, and grain surface chemistry are discussed in the context of recent observations. No present observations suggest that surface reactions are relevant, but neither can they be ruled out. Ion-molecule reactions are clearly operative, at least for the simpler species. Chemical isotope fractionation is reviewed, andd it is concluded that the complexities of the chemistry allow no cosmological conclusions to be drawn from observations of deuterium in interstellar molecules, while the presence of13C in interstellar molecules permits an estimate of the12C/13C ratio which is consistent with the current concepts of the nucleosynthesis history of the Galaxy. Possible connections between interstellar molecules and the early molecular history of the solar system are discussed.
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  • 2
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    Springer
    Calcified tissue international 23 (1977), S. 39-44 
    ISSN: 1432-0827
    Keywords: Dental cementum ; Collagen ; Protein ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary Cyanogen bromide (CNBr) peptides were prepared of the insoluble collagen of bovine dental cementum. Following chromatographic separation, the peptides were identified by their amino-acid composition. Type I collagen ([α1(I)]2α2) accounted for more than 90% of the organic matrix, while Type III collagen ([α1(III)]3) was present at a level of approximately 5%. Amino-acid analyses revealed that the CNBr peptides from α1(I) and α2 chains of cementum closely resembled the corresponding peptides from calf skin. The only systematic difference was a higher level of hydroxylation of prolyl and lysyl residues of the cementum peptides.
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  • 3
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    Springer
    Calcified tissue international 23 (1977), S. 87-94 
    ISSN: 1432-0827
    Keywords: Calcium ; Osteoporosis ; Lactation ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The calcium homeostatic mechanism was challenged in adult female rats by feeding them a calcium-deficient diet containing oxalate, and by subjecting them to pregnancy and lactation. The regimen caused a substantial weight loss, especially in those animals which reared their young well. Severe hypocalcaemia was observed in the lactating rats. Serum-P was slightly elevated. The content of hydroxyproline in serum was considerably elevated, reflecting the degree of calcium deprivation. Serum proteins were least influenced. The calcium depriving regimen reduced the growth of long bones, but did not stop it. The ash content of the bones was considerably reduced, the degree of reduction depended on the degree of calcium deprivation. Ash as percentage of total bone organ was reduced, but not to the same extent as total ash. Analyses of different parts of femur showed that the proximal and distal parts had lost more bone mineral than the diaphyseal shaft. The ash content of cortical bone tissue from the femur was estimated by a volumetric method. No differences were observed between test groups and controls, indicating that no measurable amounts of bone mineral had been removed from the walls of the vascular canals or by osteocytic osteolysis. Planimetric determinations on cross sections from femora disclosed that a great amount of bone had been removed from the endosteal surface of the diaphysis, while the periosteal surface demonstrated reduced bone apposition.
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  • 4
    Electronic Resource
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    Springer
    Pure and applied geophysics 118 (1980), S. 128-151 
    ISSN: 1420-9136
    Keywords: Galactic cosmic rays ; Solar proton events ; Particle precipitation ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract An assessment is made of the relative contribution of certain classes of energetic particle precipitation to the chemical composition of the middle atmosphere with emphasis placed on the production of odd nitrogen and odd hydrogen species and their subsequent role in the catalytic removal of ozone. Galactic cosmic radiation is an important source of odd nitrogen in the lower stratosphere but since the peak energy deposition occurs below the region where catalytic removal of O3 is most effective, it is questionable whether this mechanism is important in the overall terrestrial ozone budget. The precipitation of energetic solar protons can periodically produce dramatic enhancement in upper stratospheric NO. The long residence time of NO in this region of the atmosphere, where catalytic interaction with O3 is also most effective, mandates that this mechanism be included in future modelling of the global distribution of O3. Throughout the mesosphere the precipitation of energetic electrons from the outer radiation belt (60°≲Λ≲70°) can sporadically act as a major local source of odd hydrogen and odd nitrogen leading to observable O3 depletion. Future satellite studies should be directed at simultaneously measuring the precipitation flux and the concomitant atmosphere modification, and these results should be employed to develop more sophisticated models of this important coupling.
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  • 5
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    Springer
    Calcified tissue international 23 (1977), S. 13-17 
    ISSN: 1432-0827
    Keywords: Dental calculus ; Glycopeptide ; Chemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary A method is described for the isolation and purification of a sulphated glycopeptide from human supragingival calculus. The compound was isolated after using EDTA treatment, 2 M CaCl2 extraction, proteolytic digestion, ethanol precipitation, and finally purified by DEAE cellulose chromatography. It migrated as a single component on cellulose acetate electrophoresis, and chemical and infrared spectral analysis showed the presence of covalently attached sulphate groups. The sulphated glycopeptide was distinguished from being a sulphated glycosaminoglycan.
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  • 6
    ISSN: 1432-0827
    Keywords: Bacterial amphophile ; Purification ; Chemistry ; Resorption ; Ca influx ; Cyclic AMP
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine , Physics
    Notes: Summary The bone resorptive factor and amphipathic antigen (AcA) previously identified by us in preparations fromActinomyces viscosus have been partially purified, characterized chemically, and compared. They elute at the same location on chromatography with Ac 22. The fatty acid composition of AcA and the bone resorptive factor is the same. Some differences in carbohydrate composition are observed. TheActinomyces factor does not affect calcium influx or cyclic AMP in isolated bone cells. Therefore it is concluded that AcA stimulates resorption either by gaining entrance into bone cells or by way of a yet undetermined second messenger.
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  • 7
    ISSN: 1432-0975
    Keywords: Key words Otolith ; Chemistry ; ICP-MS ; Stock discrimination ; Epinephelus striatus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Geosciences
    Notes: Abstract  We examined the utility of otolith minor and trace element chemistry, assayed with inductively coupled plasma mass spectrometry (ICP-MS), as a means of delineating population structure in the Nassau grouper (Epinephelus striatus). We characterized the elemental composition of otoliths collected in 1993 from three locations in Exuma Sound, Bahamas and from Glover Reef, Belize in 1995. A single location in Exuma Sound was sampled in 1994 to test temporal variability in otolith composition. Five elements (Ca, Zn, Sr, Ba and Pb) were routinely detected, at levels significantly above background, by solution-based ICP-MS. Results from analysis of variance of elemental data, expressed as a ratio to Ca, indicated that there were no significant differences among the Exuma locations for any element, but significant variability was found between Glover Reef and the pooled Exuma localities for Zn/Ca, Sr/Ca and Ba/Ca ratios. Significant inter-annual differences at one Exuma Sound location was restricted to Ba/Ca ratios. Discriminant function analysis correctly classified 86% and 95% of the Belize and pooled Exuma sites, respectively. Otoliths from Belize were characterized by low Zn/Ca and high Ba/Ca and Pb/Ca ratios compared to otoliths from fish collected in Exuma Sound. Although differences in Ba levels may be related to upwelling at Glover Reef, more data are needed to definitely link otolith composition with regional differences in water chemistry.
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  • 8
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    Astrophysics and space science 224 (1995), S. 81-84 
    ISSN: 1572-946X
    Keywords: Chemistry ; Depletions ; Shocks ; IRAS 05338-0624 ; NGC 1333 IRAS 4
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract High resolution interferometer and single-dish observations of young, deeply embedded stellar systems reveal a complex chemistry in the circumstellar environments of low to intermediate mass stars. Depletions of gas-phase molecules, grain mantle evaporation, and shock interactions actively drive chemical processes in different regions around young stars. We present results for two systems, IRAS 05338-0624 and NGC 1333 IRAS 4, to illustrate the behavior found and to examine the physical processes at work.
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  • 9
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    Astrophysics and space science 233 (1995), S. 125-137 
    ISSN: 1572-946X
    Keywords: Interstellar Medium ; Dark Clouds ; Chemistry ; Bistability ; C-shock Waves
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Shock waves perturb the chemical state of the interstellar gas. We consider the effects of C-shocks on the composition of molecular clouds, for a range of values of the pre-shock gas density and magnetic induction. The time required to re-establish equilibrium in the post-shock gas depends on the initial conditions and can become very large. The significance of the two known chemical phases of dark clouds and of bistability is considered in this context.
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  • 10
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    Astrophysics and space science 233 (1995), S. 161-164 
    ISSN: 1572-946X
    Keywords: Stars ; Chemistry ; Diffusion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract We have assessed the role of diffusion in determining chemical abundances in molecular interface regions. Chemical models have been developed which include the appropriate diffusion terms and that are appropriate to a narrow diffusion region (∼0.01pc) that may exist at the interface between a dark core and a hot, shocked T-Tauri wind. We have assumed pressure balance throughout and have calculated the chemical abundances as functions of time and position through the interface. The results show that significant enhancements of detectable molecules/transitions are expected (e.g. CO J=6→5, OH and CH). Using a realistic value of the diffusion coefficient a diffusive region of dimension 0.01pc may be established within about 104 years. In general it seems likely that diffusion processes are highly significant on these and smaller lengthscales.
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  • 11
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    Boundary layer meteorology 85 (1997), S. 197-222 
    ISSN: 1573-1472
    Keywords: Turbulence ; Chemistry ; Closure ; Convective boundary layer
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract We study the interactions of chemistry and turbulent mixing of tracersin the convective boundary layer with a second-order closure model,including higher order chemistry terms. In order to limit the number of predictive equations we prescribe the profiles for ¯w¯Θ, ¯w¯θ ¯θ and the lengthscale l. However, for model validation we treat temperature and humidity asinert tracers, and compare the results with profiles observed during theAir Mass Transformation Experiment, and with similarity expressions for thesurface layer. We find good agreement of the mean profiles, but the (co-)variances are slightly underpredicted. Furthermore, the model usesdiagnostic equations expressing third moments of concentration in terms ofsecond moments and their vertical derivatives. They are compared withlarge-eddy model results, showing good agreement and, therefore, thesimplifications are justified. The model is applied to the transport of two gases subject to one bimolecular reaction. The importance of concentration correlations on themean transformation rate is studied. For two gases diffusing in oppositedirections we find for moderate and fast chemistry a 50% and90% decreased transformation rate due to the negatively correlatedconcentrations. These values are similar to large-eddy results of Schumannand Sykes et al. For two bottom-up tracers we find that the covariance ofboth reactive species is either positive or negative, increasing or reducingthe effective transformation rate depending on the Damköhler number (the ratio of the turbulent and the chemistry timescale). A significantdirect influence of chemistry on the flux divergence is found in bothcases. According to the model the effective transport to mid-levels of theboundary layer is increased when two reactive tracers diffuse in oppositedirections, and decreased in the case of two bottom-up tracers.
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  • 12
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    Journal of science education and technology 5 (1996), S. 193-201 
    ISSN: 1573-1839
    Keywords: Chemistry ; chemistry education ; multiple intelligences ; imagery ; visual-spatial thinking
    Source: Springer Online Journal Archives 1860-2000
    Topics: Natural Sciences in General , Technology
    Notes: Abstract Chemistry has evolved from a science dominated by mathematics into a science highly dependent on spatial-visual intelligence. Yet the chemical content of introductory courses remains taught essentially the same as 40–50 years ago. Chemistry, today, is recognized by chemists as the molecular science. Yet, school chemistry is alienated from that perception. Thanks to the computer, young people are more comfortable with visual imaging than their instructors were at the same age. Thus the time is rife to reinvigorate chemistry education by means of the visual-spatial approach, an approach wholly in conformance with the way modern chemistry is thought about and practiced.
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  • 13
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    New York, NY : Wiley-Blackwell
    Cell Motility and the Cytoskeleton 2 (1982), S. 225-242 
    ISSN: 0886-1544
    Keywords: spermatozoa ; calcium ion transport ; motility regulation ; cholinergic agonists ; ouabain ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Behavioral responses of mature spermatozoa treated with neurotropic factors suggest that calcium entry and intracellular transport may be regulated by a cholinergic mediated program. To test the validity of this proposed mechanism, the effect of several agents on Ca distribution in the sperm cell was examined cytochemically.Sites of Ca accumulation were visualized in thin sections of bull spermatozoa by the application of a modification of Gomori's histochemical procedure for phosphatases. Intact bull sperm cells incubated at room temperature in a buffered balanced salt solution containing 5 mM/liter of CaCl2 showed small, randomly scattered deposits of the reaction product. Similarly treated sperm cells, plasmolyzed in hypoosmotic KCl, revealed a greatly increased amount of deposit associated with the cell membranes (mitochondrial surfaces and plasmalemma), the axonemal complex components, and satellite fibers adjacent to the outer dense fibers. Preincubation of intact cells in nicotine or eserine considerably enhanced the entry of calcium into the cell and its association with the membranes and other intracellular organelles. Decamethonium, an irreversible depolarizer and blocker of cholinergic receptors, interfered with the uptake and intracellular distribution of the calcium. Ouabain, the digitalis glycoside that decreases progressive motility of bull sperm and inhibits Na-, K-ATPase, appears to block Ca efflux, causing an intense accumulation of electron-opaque particles in the plasma membrane while smaller numbers of particles are distributed sparsely throughout the cell interior.The cytochemical results showing enhanced calcium entry in the presence of cholinergic agents, depressed intracellular calcium in cells treated with cholinergic receptor blocker, and intense accumulation of calcium within the cell membrane in the presence of ouabain are consistent with spermatozoan behavioral responses to these agents. These observations support the concept that neurotropic factors may be involved in regulating transmembrane and intracellular transport of ions in control of sperm cell function.
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  • 14
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    Cell Motility and the Cytoskeleton 2 (1982), S. 309-315 
    ISSN: 0886-1544
    Keywords: tropomyosin ; avian muscular dystrophy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The isotype pattern of tropomyosin was investigated in normal and dystrophic avian pectroal muscle using two-dimensional gel electrophoresis. Previous reports have shown that adult pectoral muscle of chickens contains only the α-subunit of tropomyosin and a breast-type troponin-T (TN-T), whereas pectoral fetal muscle contains both α- and β-tropomyosin and leg-type TN-T. The change from the fetal to the adult forms begins shortly after hatching. It has been previously reported that avian dystrophic pectoral muscle contains both the leg- and breast-type TN-T; we show that in avian dystrophic muscle there is also persistent expression of the β-subunit of tropomyosin.
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  • 15
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    Cell Motility and the Cytoskeleton 2 (1982) 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 16
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    Cell Motility and the Cytoskeleton 2 (1982), S. 287-308 
    ISSN: 0886-1544
    Keywords: actin-binding protein ; Dictyostelium ; cytoskeleton ; amoeboid movement ; calcium ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A protein from Dictyostelium discoideum with an apparent subunit molecular weight of 95,000 daltons (95K protein) was previously identified as an actin-binding protein ‘Hellewell and Taylor, 1979’. In this paper, we present a method for purifying the protein, and characterize some important aspects of its structure and function. Purification of the 95K protein is achieved by fractionation with ammonium sulfate followed by chromatography on DEAE-cellulose, gel filtration on 6% agarose, and final purification on hydroxyapatite. The 95K protein is a dimer, composed of apparently identical subunits. It is a rod-shaped molecule, 38 nm in length, with a Stokes radius of 74 Å. In these structural properties, the 95K protein is similar to muscle and nonmuscle α-actinins. The 95K protein and filamin are equally competent, when compared on a weight basis, to enhance the apparent viscosity of actin as determined by falling ball viscometry. The apparent viscosity of mixtures of the 95K protein and actin is dramatically reduced at pH greater than 7.0 or free ‘Ca2+’ greater than 10-7 M. We also examine the mechanism by which calcium regulates the interaction of the 95K protein and actin. A change in free ‘Ca2+’ induces no detectable change in the quaternary structure of the 95K protein. Our experiments indicate that the 95K protein does not dramatically alter the length distribution of actin filaments in the presence of micromolar free ‘Ca2+’. A large fraction of the 95K protein cosediments with actin in the presence of low free ‘Ca2+’ (ca. 3 × 10-8M), but not in the presence of high free ‘Ca2+’ (ca. 4 × 10-6M). We conclude that increased free ‘Ca2+’ inhibits gelation of actin by the 95K protein by reducing the affinity of the 95K protein for actin. We propose that 95K protein is an important component of the cytoskeletal/contractile system in D. discoideum amoebae.
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  • 17
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    Cell Motility and the Cytoskeleton 2 (1982), S. 343-354 
    ISSN: 0886-1544
    Keywords: NBD-phallacidin ; actin ; ocular tissues ; wound repair ; stress fibers ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The fluorescent derivative of the actin-binding toxin phallacidin, 7-nitrobenz-2-oxa-1,3 diazole phallacidin, has been used to cytologically demonstrate the presence of actin in lens epithelium, corneal endothelium, and retinal pigment epithelium. In these noninjured tissues, no stress fibers are observed and fluorescence is confined mainly to an area at or near the cell membrane, although some diffuse cytoplasmic staining can also be seen. However, following injury to either the lens epithelium or corneal endothelium of rats and frogs, stress fibers are detected, but only in those cells that migrate into the wound area. Cells on the periphery of each tissue do not partake in would repair and thus maintain their normal appearance. After the tissue has regenerated, stress fibers disappear, and those cells involved in the injury response return to their normal morphology.When rabbit corneal endothelium is placed in tissue culture, stress fibers are observed as the cells migrate away from the initial explant. Upon reaching confluency, these cells spread out and each is surrounded by thick actin-containing bands. Furthermore, they exhibit some stress cables within their cytoplasm. This is in contrast to their appearance in vivo where stress fibers are absent and fluorescence is limited to a region near the cell membrane.
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  • 18
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    Cell Motility and the Cytoskeleton 2 (1982), S. 369-383 
    ISSN: 0886-1544
    Keywords: motility ; flagella ; cilia ; microtubules ; Gregarines ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The male gametes of the parasitic protozoan, Lecudina tuzetae, have a motile flagellum with a “6 + O” ultrastructure ‘Schrével and Besse, 1975’. These gametes were isolated from the cysts in which they develop and were observed and photographed under a variety of conditions. The flagella beat continuously, without stopping and starting, with a beat period of about 2 sec. They can beat in solutions whose viscosities are greater than 0.5 Nsm-2 (l Nsm-2 = 103 cP). The waveform can be approximated by a series of helical arcs and interconnecting straight regions that travel from the base to the tip. The helical regions have a radius of curvature of 3.2 μm and subtend a final angle of 1.7 radians. The straight portions are 2.0 μm in length. There are two sets of opposing bends, but they do not originate in the same plane. The resulting waveform is an approximately helical coil, with a pitch of 9.8 μm, a pitch angle of 0.6 radian and a peak-to-peak amplitude of 2.3 μm. The sense of the coil is left handed. The axoneme twists during beating. The main differences between the movement of this flagellum and that of typical 9 + 2 flagella are a low beat frequency and three-dimensional bends that produce relatively little forward movement of the cell. Twisting is discussed as a means of discriminating between some types of models of flagellar motility.
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  • 19
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    Cell Motility and the Cytoskeleton 2 (1982), S. 429-443 
    ISSN: 0886-1544
    Keywords: 21S dynein ; tubulin ; binding stoichiometry ; ATP sensitivity ; binding cooperativity ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The binding properties of Tetrahymena 21S dynein to doublet A and B subfiber microtubules were analyzed by both a turbidimetric assay (Δ A350 nm) and electron microscopy. KCl-extracted, sucrose-gradient, purified 21S dynein binds to each of the two kinds of axonemal microtubules in both ATP-insensitive and ATP-sensitive modes, even though only a single type of binding occurs to each of the subfibers in situ. Total dynein bound to axonemal microtubules is a composite of binding that is sensitive to dissociation by ATP and binding that is insensitive to ATP. Each exhibits a different binding profile. Total binding exhibits a sigmoid profile (h = 1.93) and saturates at 1.49 mg D/mg T. ATP-sensitive binding likewise exhibits a sigmoid profile (h = 2.66) but saturates at 1.06 mg D/mg T. Binding occurs with a similar affinity for both A and B subfibers. The Hill coefficient (h) for ATP-sensitive binding implies positive cooperativity between binding events. ATP-insensitive binding was studied independently in 20 μM ATP, 10 μM vanadate, which blocks ATP-sensitive binding. ATP-insensitive binding exhibits a hyperbolic profile (h = 1.0) and likewise occurs along each of the two kinds of axonemal tubules. Binding saturates at 0.87 mg D/mg T. The binding data suggest that the tubulin dimer has conserved both ATP-sensitive and ATP-insensitive binding sites for 21S dynein, even though the sites may not be expressed in vivo.
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  • 20
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    Cell Motility and the Cytoskeleton 2 (1982), S. i 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 21
    ISSN: 0886-1544
    Keywords: flagella ; cilia ; trachea ; microtubules ; crowns ; microtubule assembly ; caps ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The distal tips of the central pair and A-microtubules are capped in mammalian and avian tracheal cilia. The capping structures are similar to those found in protozoan cilia and flagella [Dentler, 1981], and consist of a central microtubule cap that links the central microtubules to the membrane or to the ciliary crown and A-microtubule plugs that insert into the lumen of each of the A-microtubule plugs is bound to the central microtubule cap by distal filaments. The ends of the central and outer doublet microtubules are tightly bound to the cap in both intact and in demembranated and reactivated tracheal cilia. Analysis of the displacement of the microtubule tips in cilia fixed at various bend angles revealed that the displacements of A-microtubules are only partially in agreement with those predicted by the sliding filament model [Satir, 1968]. These results are discussed with respect to the regulation of microtubule sliding in capped cilia and the role of the microtubule capping structures in microtubule assembly.
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  • 22
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    Cell Motility and the Cytoskeleton 2 (1982), S. 19-24 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
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  • 23
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    Cell Motility and the Cytoskeleton 1 (1981), S. 329-347 
    ISSN: 0886-1544
    Keywords: actin ; microfilaments ; heavy meromyosin ; mammary gland ; secretion ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cytochalasin B, a microfilament-altering drug, inhibits lactose synthesis in lactating guinea pig mammary gland [Biochim. Biophys. Acta 392:20, 1975] but not primarily by inhibiting glucose transport [Eur. J. Cell Biol. 20:150, 1979]. In order to study the possible role of microfilaments in lactose synthesis and secretion, we isolated both the alveolar (milk-secreting) and myoepithelial (contractile) cells from lactating mammary gland. Light microscopy shows that the alveolar cell fraction (viability approximately 71%) is homogenous and that the cells retain strong polarity of secretory structures in the apical region. Two proteins were extracted from the alveolar cell fraction. One (mol wt 42,000) comigrates with skeletal muscle actin on SDS-PAGE gels. The other, a high-molecular-weight (180,000) protein (HMWP) may be analogous to actin-binding protein or clathrin. An extract from the myoepithelial cell fraction also contains a protein that comigrates with actin but no HMWP. Whole tissue extract contains the 42K protein, and a 185K HMWP. Examination of the alveolar cell extract by electron microscopic (EM) negative staining revealed meshworks of multistranded, interconnecting filaments, with attached globular structures (100-200 A) (possibly the HMWP) and single filaments (40-60 A diameter) branching off. To localize these filamentous structures in situ, whole tissue was glycerinated and incubated with rabbit skeletal muscle heavy meromyosin (HMM). Masses of filaments in myoepithelial cells served as convenient standards for HMM decoration. Decorated filaments have cross-arms or projections, unlike the narrow, smooth filaments of control tissue. Decorated filaments in alveolar cells are located beneath the plasma membrane, in close association with secretory vacuoles, and near the Golgi apparatus; filaments near the latter two are often oriented perpendicular to the plasma membrane. Microvesicles are embedded in meshworks under the plasmalemma and near the Golgi apparatus. Intermediate-sized (85-115 A diameter), non-decorated filaments diverge from the meshworks of decorated filaments. Microvesicles are associated with intermediate-sized filaments as well. The association of actin-like filaments with secretory vacuoles and microvesicles and their location in areas of the cell concerned with biosynthetic activities suggest a possible function in the intracellular transport of secretory products.
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  • 24
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    Cell Motility and the Cytoskeleton 2 (1982), S. 165-168 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 2 (1982), S. 199-204 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 2 (1982), S. 71-75 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 3 (1983), S. 93-103 
    ISSN: 0886-1544
    Keywords: bacterial motility ; flagella ; sheathed flagella ; complex flagella ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Although bacterial flagellar sheaths were observed over 30 years ago, they may still be characterized as structures in search of a function. In addition to true sheaths, bacterial flagella may possess other adornments that cause an increase in the organelle's cross-sectional diameter. These “complex flagella” are sharply differentiated from sheathed flagella. Immunological and chemical distinctions have been found between flagellar sheaths, flagellar cores, and LPS layers inferred to be the sheath sensu stricto. Although complex flagella may serve as specific receptors for flagellotropic phages or in allowing for more efficient swimming in viscous environments, similar functions have not yet been attributed to true sheaths. It is postulated that flagellar sheaths may allow for specific interaction between a bacterium and a surface. In addition, there is a problem as to the relationship between a rapidly rotating flagellum and the sheath.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 113-121 
    ISSN: 0886-1544
    Keywords: coelomocytes ; filopodia ; whole cell translocation ; video microscopy ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have utilized a video-enhanced contrast system coupled to a DIC-equipped microscope to examine the motility of both whole coelomocytes and individual filopodia. When the cells are left in diluted coelomic fluid, they exhibit a fibroblast-like mode of translocation across the substrate. These cells extend lamellipodia at their advancing margin and develop retraction fibers at the trailing edge. Filopodia are actively extended from the lamellipodia of the advancing margin. Cells that are washed free of the coelomic fluid and placed in an isotonic buffer lose their ability to translocate. Filopodia on these stationary cells are seen to undergo a series of waving and bending motions. These motions are rapid and result in a filopodium folding back upon itself only to reextend later. Both forms of motility are discussed in light of the existing structural and biochemical knowledge of this and other cell types.
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    Cell Motility and the Cytoskeleton 1 (1981), S. 387-397 
    ISSN: 0886-1544
    Keywords: birefringence ; polarizing microscope ; sea urchin egg ; cortex ; mitosis ; cleavage ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Birefringence (BR) at the cell surface of fertilized eggs of the sand-dollar, Clypeaster japonicus, during mitosis and cleavage was determined with a photoelectric BR detection apparatus [Hiramoto et al, 1981a]. The cortex of about 2 μm thickness is birefringent positive with respect to the normal to the cell surface. The hyaline layer is negatively birefringent. The halo-layer consisting of a row of microvilli surrounding the egg is positively birefringent in normal Ca-free sea water, while it is negatively birefringent in Ca-free sea water with high refractive index. The BR of the cortex gradually increases over the entire surface during mitosis until the onset of cleavage. The BR of the cortex at the polar region reaches a maximum shortly after the onset of cleavage and then decreases, while the BR of the cortex at the equatorial region begins to decrease shortly before the onset of cleavage, reaches a minimum shortly after the cleavage starts, and then increases again as the cleavage furrow advances. The coefficient of birefringence of the cortex is about 2.5 × 10-5 at the maximum. The BR change of the cortex during mitosis and cleavage is interpreted as a passive deformation caused by the constriction of the contractile ring as well as an active structural change of the cortex occurring in the dividing cell.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 213-226 
    ISSN: 0886-1544
    Keywords: microtubules ; fertilization ; cell division ; sea urchin ; cytoskeleton ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The microtubule-containing structures that appear in eggs during fertilization and cell division in the sea urchins Lytechinus variegatus and Arbacia punctulata were detected by antitubulin immunofluorescence microscopy of detergent extracted cytoskeletal preparations. The extraction buffer, which is composed of 0.55 mM MgCl2, 10 mM EGTA, 25 mM MES, 25% glycerol, 1% Nonidet P-40, and 25 μM PMSF, pH 6.7, allows for dramatically improved fluorescent images compared to those obtained using conventional staining procedures, with residual background staining being reduced to near zero.The immunofluorescent images obtained using this technique provide information on several motile events that occur during the first cell cycle. This technique demonstrates that all of the cytoplasmic microtubules are associated with the incorporated sperm's centrioles during female pronuclear migration. This changes during the centration of the male and female pronuclei at which time a monastral array of microtubules forms in the egg's cytoplasm. A large proportion of the monastral microtubules do not appear to be associated with the centrioles. At prophase and early metaphase, the centrioles are the dominant microtubule organizing centers (MTOCs) consistent with mitotic theories that the kinetochore catches, but does not initiate, microtubules. Observations of intercentriolar distances show that there are three stages of pole separation during the first cell cycle. The initial separation occurs during pronuclear centration, the second during the streak stage, and the final one during the late stages of mitosis. At telophase, polar microtubules appear to extend into the cortex supporting the cell surface at all regions except the presumptive cleavage site.
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    Cell Motility and the Cytoskeleton 3 (1983) 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 3 (1983), S. 273-280 
    ISSN: 0886-1544
    Keywords: Chlamydomonas flagellar collars ; Chlamydomonas cell wall ; mating in Chlamydomonas ; cell wall proteins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The flagella of Chlamydomonas reinhardtii protrude through the cell wall via short, tunnel-like openings that are lined with 11 nm × 500 nm fibers arranged in parallel array. These cylindrical collections of fibers presumably permit free movement of the flagella within the cell wall. In this report electron-microscopic evidence is presented showing that during the initial stages of the mating reaction intact collars slip off of the ends of the flagella when cell wall loss occurs. Electrophoretic analysis of isolated collars reveals one major protein and several minor species.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 333-347 
    ISSN: 0886-1544
    Keywords: Caenorhabditis elegans spermatozoa ; cell motility ; electron microscopy ; cell-substrate contact ; 2-nm filaments ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The locomotion of C. elegans spermatozoa resembles, in many respects, the crawling movements of other eukaryotic cells. However, these sperm contain surprising little actin, which plays no apparent role in this cell's motility. Electron microscopy has revealed that crawling spermatozoa retain a strict morphological polarity so that the organelle-filled cell body is separated from the pseudopod by an array of cytoplasmic laminar membranes. When sperm crawl only the pseudopod contacts the substrate; the cell body is either pulled behind or carried on top of the rear portion of the pseudopod. Fingerlike projections which extend forward from the leading edge of the pseudopod initiate contact with the substrate. The underside of the pseudopod exhibits areas of close (40 nm separation) membrane-substrate association with intervening areas of wide (up to 300 nm) membrane-substrate gaps. The pseudopod cytoplasm contains 2-nm filaments but no filamentous actin has been observed. These 2-nm filaments were detected in thin sections of crawling cells and in negative-stained remnants of spermatozoa disrupted by either hypotonic buffer on Triton X-100. The filaments are found both free in the cytoplasm and closely associated with the cytoplasmic face of the plasma membrane and are usually oriented along the long axis of the cell. Neither the identity nor the function of these filaments has been established although their location and orientation suggest that they may be involved in generating propulsion.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 349-361 
    ISSN: 0886-1544
    Keywords: myosin phosphorylation ; actin polymerization ; chemotactic factors ; leukocytes ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Changes in the state of polymerization of actin and phosphorylation of myosin have been observed in polymorphonuclear leukocytes (PMNs) soon after the addition of the chemotactic peptide N-formylnorleucylleucylphenylalanine. At a time when the cells are observed to extend many ruffles or lamellipodia from their surface, the fraction of the cellular actin present in a monomeric form is decreased by about 25% as assayed by the ability of the G-actin to inhibit DNAase. These changes are temporally correlated with an increase in the staining by nitrobenzooxadiazole (NBD)-phallacidin, a probe that binds F-actin selectively. The NBD-phallacidin staining is observed in the surface ruffles. When the peptide concentration is decreased by addition of a tenfold excess of buffer, cells withdraw their surface ruffles and form blebs. These changes correlate with an increase in the G-actin levels detected with the DNAase inhibition assay. An increase in phosphorylation of the 20,000-dalton light chain of myosin is also observed in leukocytes stimulated by addition of chemotactic peptide. These observations of changes in cytoskeletal proteins of PMNs provide a beginning for further studies on the regulation of cell motility by chemotactic factors.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 391-397 
    ISSN: 0886-1544
    Keywords: focal contacts ; microfilaments ; microinjection ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The role of structural elements in the organization and maintenance of focal contacts was studied by microinjecting into tissue culture cells specific probes which interfere with filamentous actin or with vinculin: actin interaction. Injection of actin capping proteins from Physarum and brain resulted in breakdown of microfilament bundles starting at their distal ends and in loss of focal contacts. This process was fully reversible. Injection of a high affinity antibody against chicken gizzard vinculin led to partial breakdown of microfilament bundles concomitant with disruption of focal contacts with vinculin remaining at the plasma membrane. This process was irreversible.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 431-438 
    ISSN: 0886-1544
    Keywords: myotendinous junction ; laminin ; type IV collagen ; heparan sulfate proteoglycan ; alpha actinin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The muscle-tendon junction of murine skeletal muscles has been analyzed by a variety of extraction techniques, by myosin subfragment-1 binding experiments, and by ultrastructural immunocytochemistry. The results indicate that the muscle-tendon junction is composed of four distinct domains: an intracellular domain, the internal lamina; a domain connecting the internal lamina with the lamina densa of the external lamina, the connecting domain; the lamina densa; and a domain which attaches the lamina densa to the collagen fibers, the matrix. Each of these domains is distinct with respect to position, three-dimensional organization, and molecular composition, and is therefore considered to have a unique role in the transmission of contractile force.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 463-483 
    ISSN: 0886-1544
    Keywords: intracellular matrix ; extracellular matrix ; covalently cross-linked matrix ; ε-(γ-glutamic) lysine bonds ; skeletal muscle ; titin ; covalently cross-linked collagen ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: When skeletal, cardiac, and smooth muscle is exhaustively extracted with a protein-unfolding reagent such as 6 M guanidine HCl and a disulfide-reducing reagent such as 5% β-mercaptoethanol, a tissue ghost remains intact and retains the characteristic shape and dimensions of the tissue before extraction. In the case of chicken pectoral muscle, the tissue ghost contains 1% of the original muscle proteins. Guanidine HCl extraction followed by collagenase treatment of glycerol-extracted chicken pectoral muscle releases a clean preparation of elongated structures containing 0.2% of the original protein and representing the covalently cross-linked remnants of the muscle fibers. The material of these muscle fiber ghosts extends throughout the interior of the cell. Antibodies raised against the tissue ghosts of smooth muscle cross-react with glycerol extracted skeletal myofibrils, forming a banding pattern which coincides with the banding pattern observed when myofibrils are reacted with antibodies against titin. Titin, a large and soluble protein found in skeletal muscle, cross-reacts with our antigizzard antibody. However, amino acid analysis of the muscle fiber ghosts indicates that titin cannot be the only subunit of the insoluble polymer, but that one or more proteins with a very high glycine and alanine content and a very low basic and acidic amino acid content must also form part of the covalently cross-linked matrix. The possibility is presented that this matrix may be the basis of the superthin 2-3-nm filaments which have been observed in a variety of cell types.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 513-524 
    ISSN: 0886-1544
    Keywords: fertilization ; actin ; microfilaments ; sea urchin ; cell division ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The sea urchin egg at fertilization is an ideal model in which to study actin-mediated surface activity. Electron microscopy of unfertilized eggs demonstrates the presence of thousands of well-arrayed short microvilli, which appear supported by cytochalasin-sensitive actin oligomers as detected with rhodamine-labeled phalloidin staining of permeabilized eggs. At insemination, the previously short microvilli elongate and cluster around the successful sperm during incorporation. Phalloidin staining demonstrates a tremendous recruitement of polymerized actin into the site of sperm incorporation, resulting in the formation of the fertilization cone. Fertilization of cytochalasin-treated eggs results in the normal activation of the metabolic and bioeletric events, but sperm incorporation does not occur since the localized actin assembly required for fertilization cone formation is precluded. After sperm incorporation, the entire fertilized surface is restructured, as a result of a massive polymerization of actin to produce a burst in microvillar elongation. Addition of cytochalasin to eggs immediately following sperm incorporation demonstrates the recruitment of actin assembly for the proper progression through the first cell cycle. During normal cell divison, the egg surface retains the long microvilli. The furrow which forms at cytokinesis does not appear as a unique new structure, but rather as a reorganization of the cortical microfilaments. Quantitative fluorescence microscopy argues against an increase in microfilaments during early cytokinesis. At the latest stages of cytokinesis, a thickening of the cortical actin is noted, which could possibly be interpreted as a contractile ring. A minor basal level of actin assembly with numerous nucleation sites in unfertilized eggs and a tremendous but localized assembly of microfilaments surrounding the sperm during incorporation, followed by a massive global microfilament assembly event to elongate the fertilized egg microvilli resulting later in the reorganization of these microfilaments to produce the forces necessary for cytokinesis, highlight the utility of the study of sea urchin eggs at fertilization for understanding actin-membrane interactions.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 553-565 
    ISSN: 0886-1544
    Keywords: microfilaments ; cytoskeleton ; simian virus 40 ; cell adhesion ; cell surface ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In order to assess the role of cytoskeletal structure in modulating cell surface topography during cell transformation, cytoskeletal organization of 3T3 mouse cells transformed with a tsA mutant of simian virus 40 (SV40) was studied in detail by correlative light and electron microscopy. Detergent-extracted, criticalpoint dried whole cells observed in the electron microscope were seen to contain well-organized microfilament bundles (stress fibers) traversing the longitudinal axis of cells grown at the restrictive temperature (39°C). When grown at the permissive temperature (32°C), cells prepared in this manner were not observed to contain such structures. However, when semithin sections (0.5 μm) were viewed by transmission electron microscopy at 120 kV, short microfilament bundles were seen in 32°C-grown cells. There was an alteration in the morphology of these structures at sites of attachment to the substratum (focal contacts), and they were shorter in length than microfilament bundles of 39°C-grown cells. A difference was also observed between the two phenotypes in the layer of microfilaments associated with the dorsal cell surface. Since it is this layer that directly determines cell surface architecture, it is proposed that changes in microfilament bundle-generated surface tension are responsible for alterations of this layer, leading to an altered cell surface morphology. Tension may be modified by disturbances in focal contacts (or adjacent regions) or altered actin-associated protein(s).
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    Cell Motility and the Cytoskeleton 3 (1983), S. 609-622 
    ISSN: 0886-1544
    Keywords: erythrocyte membrane ; surface elastic shear modulus ; membrane viscosity ; hereditary disorders of blood ; membrane yield ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Measurements of the mechanical properties of the erythrocyte membrane provide a direct assessment of the proper function of its structural components. To assess the effects of alterations in molecular structure on membrane mechanical properties, measurements have been performed on cells from six individuals whose membranes contain inherited, biochemically characterized structural defects. Because the contribution of the memmbrane skeleton to the mechanical behavior of the membrane is most evident in shear deformation, mechanical experiments were performed to measure the material constants which characterize the response of the membrane to shear force resultants. The surface elastic shear modulus characterizes the elastic response of the membrane; the yield shear resultant is the maximum shear force resultant which the membrane can support elastically; and the plastic viscosity coefficient characterizes the rate of membrane deformation when the elastic limit has been exceeded.Generally, it was found that when the molecular defect is found to occur in a region of the skeleton which is stress-supporting, the maximum elastic strength of the membrane is reduced. However, the magnitude of the reduction can be quite different for membranes having similar or even identical defects. In some cases the differences can be attributed to the removal of the most fragile cells of the population by the spleen, but other results indicate that the biochemical description of the defects may be incomplete. These results emphasize the need for further refinements both in the biochemical characterization of membrane skeleton structure and in the description and measurement of membrane mechanical properties.
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    Cell Motility and the Cytoskeleton 4 (1984), S. 129-135 
    ISSN: 0886-1544
    Keywords: amoeboid motion ; chemoattractants ; chemotaxis ; Dictyostelium ; filopodia ; folic acid ; pterins ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Living vegetative D. discoideum amoebae were studied to determine whether their filopodia respond to folic acid, a chemoattractant for these cells. Exponentially growing amoebae (ca. 10 μm diameter) exhibit 5-30 μm long filopodia; at stationary phase, aggregation competent amoebae have numerous multibranched filopodia up to 100 μm long. Folic acid was observed to stimulate production, elongation, and branching of filopodia with its effects progressively changing as the amoebae approach aggregation. Filopodial construction was also found to be dependent upon Mg2+ levels. The significance of these results is discussed with respect to progressive changes within the vegetative phase as well as to the mechanisms of amoeboid movement, pseudopodial activity, and chemotaxis.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 649-655 
    ISSN: 0886-1544
    Keywords: axonal transport ; lymphocyte capping ; spectrin ; fodrin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Fodrin is an actin/calmodulin-binding protein with similarities to spectrin (erythrocytes) and TW 260/240 (brush border). It is concentrated beneath the plasma membranes of neurons and other cells. We have observed translocations of fodrin in both neurons and lymphocytes. Newly synthesized, radiolabeled fodrin moves down axons at a maximum velocity (about 50 mm/day) that is slower than the most rapidly axonally transported proteins (group I). A portion of fodrin appears to move more slowly at velocities (1-10 mm/day) resembling those of actin and myosin (group IV) and tubulin and neurofilament proteins (group V). In lymphocytes, when certain surface antigens are induced by cross-linking agents to migrate to one pole of the cell and form a cap, fodrin redistributes beneath the membrane and forms a subcap. The movements of fodrin in lympohocyte capping and in the axonal transport of group IV polypeptides have certain similarities. In both cases, the redistribution of fodrin is accompanied by concomitant redistributions of actin, myosin, and calmodulin, and both processes proceed at similar velocities. We consider the possibilities that these two processes are related, both being driven by a submembrane force-generating system comprising in part actin, myosin, and fodrin, and that fodrin serves to link various organelles or proteins to this system.
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    Cell Motility and the Cytoskeleton 4 (1984), S. 1-5 
    ISSN: 0886-1544
    Keywords: motility ; power output ; muscle ; flagella ; cytokinetic furrow ; mitotic spindle ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cellular motile systems as diverse as muscle and the mitotic spindle have been compared by their specific power output: the maximum power they develop per unit of engine volume. Striated muscles and flagella have high specific output; their performance is comparable to that of typical automobile engines. The cytokinetic furrow and the mitotic spindle have very much lower specific power output. The furrow's output is 7,000 times lower than muscle and the spindle's is 300,000 times lower. Different macromolecules have been used to generate power in systems with similar output (muscles and flagella) and, conversely, the same macromolecular motor has been used in systems with very different output (muscles and cytokinetic furrows). The common feature amid this diversity is adaptation to a particular biological role, which specific power output reflects very well. High values are found where a powerful, compact engine should be advantageous, while low values are found where precision, not power, matters most.
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    Cell Motility and the Cytoskeleton 4 (1984), S. 76-76 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 2 (1982), S. 73-82 
    ISSN: 0886-1544
    Keywords: desmids ; videomicrography ; photokinesis ; photophobic response ; photophosphorylation ; photosynthesis ; phototaxis ; uncouplers ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The effects of the uncouplers CCCP and DNP on photokinesis, phototaxis, and the photophobic response in the desmid Cosmarium have been studied both in population systems and by videomicrographic, single-cell analysis. Light-dependent motility is specifically inhibited by both uncouplers, indicating that photokinesis is driven by photophosphorylation. In population experiments, phototaxis and accumulations in light traps due to photophobic responses are inhibited by drug concentrations comparable to those that inhibit photokinesis. Analysis of single-cell behavior demonstrated, however, that neither photophobic responses elicited by an increase in light intensity (step-up response) nor by a decrease (stepdown response) are inhibited, as long as the reduced motility allows the organisms to cross a light--dark border. Phototactic orientation is not impaired by DNP in the single cell analysis, but CCCP significantly reduced the degree of orientation. The results indicate that, although chlorophyll is the photoreceptor for all three photoresponses, at least the photophobic response is independent of both the photosynthetic electron transport chain and photophosphorylation.
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    Cell Motility and the Cytoskeleton 2 (1982), S. 91-92 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 2 (1982) 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 2 (1982), S. 93-101 
    ISSN: 0886-1544
    Keywords: cell motility ; singlet microtubules ; dynein ; coccid insect ; aflagellate spermatozoa ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In this report we demonstrate that in the coccid insects Pseudococcus, Phenacoccus, and Planococcus the whole spermatozoon is made up by a nuclear central core surrounded by two complete and one incomplete turns of concentric microtubule palisades. Microtubules of the outer row are linked by a system of short projections 6 nm long; those of the inner row are linked to each other by similar arms; a second system of 6 nm arms links the tubules of each inner row to those of the respective outer row. All these systems of arms are longitudinally spaced every ∼ 12 nm. The motility of this spermatozoon is due to waves progressing from the posterior extremity to the anterior one. By SDS polyacrylamide gel electrophoresis a group of high molecular weight polypeptides is detected, one of which migrates in coincidence with the A dynein band from sea urchin sperm. Our data suggest that occurrence in coccid spermatozoon of a motility due to singlet tubules-dynein interaction.
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    Cell Motility and the Cytoskeleton 2 (1982), S. 103-113 
    ISSN: 0886-1544
    Keywords: actin ; cleavage ; fluorescein-labeled phalloidin ; microinjection ; phalloidin ; sand dollar eggs ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Effects of microinjection of phalloidin on fertilization and cleavage of sand dollar (Clypeaster japonicus and Scaphechinus mirabilis) eggs were studied. The drug, previously injected into unfertilized eggs, showed no effect on the elevation of the fertilization membrane upon insemination up to an intracellular concentration of 50 μM. However, the movement of the egg pronucleus to the sperm pronucleus was inhibited and the fusion of pronuclei did not occur. The subsequent development no longer took place. When phalloidin was injected into fertilized eggs, the thickness of the cortical layer increased and the microvilli became conspicuous. Both nuclear division and cleavage were inhibited at the intracellular concentration of more than 20 μM, though the latter seemed to be more sensitive to phalloidin than the former.Fluorescein-labeled phalloidin (FL-phalloidin) was injected into eggs in order to investigate F-actin localization by fluorescence microscopy. In both unfertilized and fertilized eggs, FL-phalloidin was localized in the cortical layer within 1 min after injection. It was also localized in the cortical layer as radially oriented rodlike structures when injected into fertilized eggs before the disappearance of the nuclear membrane. No distinct fluorescence was detected in the mitotic apparatus or in the cleavage furrow. FL-phalloidin redistributed gradually into egg cytoplasm. In unfertilized eggs, fluorescent rods were found especially in the egg pronucleus 30 min after injection.
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    Cell Motility and the Cytoskeleton 2 (1982), S. 131-147 
    ISSN: 0886-1544
    Keywords: higher land plant contractile system ; actin activation of myosin ; S-1 decoration of actin ; polymerization of actin ; calcium sensitivity of actomyosin interaction ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: This paper describes the initial isolation of actin- and myosin-like proteins from the cytoplasm of the endocarp tissue cells of the fruit of the tomato, Lycopersicon esculentum. Low ionic strength buffers extracted the 42,000 molecular weight tomato actin in the depolymerized form. Tomato actin can be polymerized in 0.1 M KCl, 2 mM MgCl2 to form 6 nm diameter filaments resembling rabbit skeletal muscle F-actin in their ultrastructure and pattern of decoration with rabbit myosin subfragment-1 (S-1). Tomato F-actin activates the low ionic strength Mg2+ ATPase of rabbit S-1 up to ten-fold. High ionic strength extracts of tomato yield a myosinlike enzyme whose ATPase activity in 0.5 M KCl is maximal in the presence of K+-EDTA and is repressed in the presence of Mg2+. The column-purified enzyme forms a complex with rabbit F-actin, which can be dissociated by Mg2+ ATP. The low ionic strength Mg2+ ATPase of tomato myosin can be activated ten-fold by rabbit actin and up to nineteen-fold by tomato actin. No activation of the tomato myosin by rabbit F-actin occurs in the absence of free calcium ions.
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    Cell Motility and the Cytoskeleton 2 (1982), S. 149-161 
    ISSN: 0886-1544
    Keywords: cell locomotion ; gastrulation ; contact paralysis ; collagen substratum ; serum factors ; morphogenetic movements ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Prospective mesodermal cells of Xenopus laevis gastrulae showed substantial locomotion in vitro, averaging 4.3 μM/min, when dissociated and cultured on a glass surface coated with collagen and fetal bovine serum. The cell translocate by making lamellipodia and filopodia whereas the main cell body remains rounded. When two mesodermal cells made contact with each other, they showed contact paralysis of lamellipodial activity. In contrast, when mesodermal cells contact ectodermal cells, contact paralysis does not occur. Rather, migrating mesodermal cells continue to translocate. The locomotion in vitro appears to mimic that in vivo during gastrulation, because of the similarities of the rate of movement and the cell shape in culture and in embryos. Neither prospective ectodermal cells from gastrulae nor prospective mesodermal cells from blastulae showed locomotion under the same culture conditions.
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    Cell Motility and the Cytoskeleton 2 (1982), S. 191-194 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 3 (1983), S. 167-184 
    ISSN: 0886-1544
    Keywords: saltatory organelle movements ; ciliary movement ; dynein ; vanadate ; microinjection ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: To test the idea that saltatory organelle movements of nonmuscle cells might be driven by microtubule-dynein interactions, we microinjected vanadate into several different types of cultured cell. Solutions of sodium metavanadate made up in a simple buffered salt solution were pressure microinjected into fully spread cells in an open-topped culture chamber placed on the stage of an inverted microscope. The cells were observed by oil-immersion phase-contrast optics and results were recorded on movie film. Vanadate, at 10-5-10-2 M, microinjected into cultured chick embryo fibroblasts, failed to inhibit organelle movements. To test the effectiveness of vanadate's inhibitory action under living cell conditions, ciliated epithelial cells were micro-injected. In these cells even the smallest microinjection of 5 × 10-5 M vanadate caused an immediate cessation of ciliary beating. Moreover, in cells that were well spread it was found that whereas vanadate, at 5 × 10-5 × 10-3M, inhibited ciliary motion, it failed to inhibit organelle saltations in the same cell. To determine whether vanadate would inhibit a living actin-myosin system, myocardial cells were also microinjected. Following microinjection of 5 × 10-5 and 5 × 10-4M vanadate a temporary tonic contraction (which also occurred following microinjection of buffer alone) was followed by regular beating. Taken together these results demonstrate that in living cell systems microtubule-dynein interactions are as sensitive to vanadate inhibition as they are in demembranated model systems, and that a working actin-myosin system in a living muscle cell does not share this great sensitivity. In light of the pronounced differential inhibitory effects of vanadate on the movements of cilia and organelles, our results suggest that saltatory organelle movements in chick embryo fibroblasts and rabbit oviduct epithelial cells are unlikely to be brought about by microtubule-dynein interactions.
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    Cell Motility and the Cytoskeleton 3 (1983) 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 3 (1983), S. 247-259 
    ISSN: 0886-1544
    Keywords: spermatozoa ; Ciona ; axoneme ; quiescence ; twist ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A simple planar model of sliding can predict the amount of sliding required to form a certain degree of bend. The accuracy of this prediction relies on the assumptions that no twists occur in the axoneme and that no sliding occurs at the base. However, previous studies indicated that twists may occur.This paper explores a new method for quantitating and analyzing twists. Preliminary results using this method showed that there were twists. In order to control for possible artifacts due to fixation and other preparative procedures, the characteristic S-shaped quiescent state of Ciona spermatozoa was studied.Analyses of platinum replicas of those flagella in which this waveform is well preserved suggest that most, if not all, of the twists observed are due to the artifact of a curved shape settling onto a surface. Detailed analyses indicate that if twists do occur in quiescent sperm, they are probably less than 0.4 radian. Since axonemes are evidently easily twisted in rigor, and even after fixation, caution should be exercised in interpretation of axonemal twists.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 261-271 
    ISSN: 0886-1544
    Keywords: chromosome movement ; meiosis ; spermatocytes ; prophase ; nuclear envelope ; aster ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Association of bivalent chromosomes with the astral centers and nuclear envelope was analyzed in crane-fly spermatocytes during the final hours of diakinesis. In contrast to other systems in which movement of chromosomes during diakinesis correlates with the clustering of bivalents near the astral centers, such clustering is not prevalent in crane-fly spermatocytes. Polarization indices of bivalents calculated 5 to 10 minutes before the end of diakinesis provided evidence for polarization of only a fraction of all bivalents. Similar results were obtained in a large number of fixed cells in which asters and chromosomes were preferentially stained. Ultrastructural analysis of cells in late diakinesis revealed significant contact between bivalents and the nuclear envelope in all 46 cells that were analyzed. The extent of contact in some cells was greater than in others. Sites of contact included the telomeric ends of bivalents, and in some cases the distribution of contact sites suggested the possible involvement of centromeres in chromosome-nuclear envelope association. The results are consistent with the hypothesis that a dynamic interaction between chromosomes and nuclear envelope may exist during late prophase, when the movement of chromosomes is known to occur.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 283-305 
    ISSN: 0886-1544
    Keywords: taxol ; microtubules ; intermediate filaments ; fibroblasts ; epithelial cells ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Taxol promotes microtubule (MT) assembly in vitro and induces the reorganization of the cytoskeleton into unusual MT arrays in cultured cells. The possibility that taxol also has an indirect effect on intermediate filaments (IF) was investigated. In baby hamster kidney (BHK-21) and human skin (ENSON) fibroblasts treated with 1-10 μM taxol for 1-24 h, the drug induces changes which are similar to those produced by colchicine. These include a loss of major cellular extensions, a redistribution of organelles to a perinuclear location, and an inhibition of locomotion. Saltatory particle movements are not inhibited, however. Ruffling and filopod formation continue, indicating that cells are viable up to 24 h.Polarized light microscopy of living fibroblasts treated with taxol reveals the presence of perinuclear birefringent material which has been examined by immunofluorescence. In control cells, IF and MT radiate from a juxtanuclear region and extend to the cell periphery. In taxol-treated cells, MT and IF are excluded from cell margins, forming large central bundles.In the epithelial cell lines PtK2 and PAM, the keratin system of IF does not become redistributed; in PtK2, however, a second fibroblastlike system of IF does become redistributed to a perinuclear position during taxol treatment.Ultrastructural analyses show that taxol-treated fibroblasts contain parallel arrays of cross-bridged MT-IF as well as bundles of MT exclusive of IF. Epithelial cells contain a predominance of IF-free MT bundles which are organized into hexagonally packed arrays. In these bundles MT frequently exhibit hooks or other incomplete MT profiles and are linked by filamentous material.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 375-382 
    ISSN: 0886-1544
    Keywords: actin ; spectrin ; band 4.1 ; cytochalasins ; erythrocyte ; brain ; actin-membrane attachment ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A complex of proteins with properties similar to those of erythrocyte spectrinband 4.1-actin complex has been idientified in a preparation derived from bovine brain. The complex has an apparent sedimentation coefficient of about 26S, and contains brain spectrin (also called fodrin) and actin as major components. The actin in the complex is in the oligomeric form, which nucleates assembly of actin filaments that grow from the “barbed” end. The complex cross-links actin filaments, resulting in an increase in low-shear viscosity. Whether the complex contains a protein analogous to erythrocyte band 4.1 is not known. However, it can be demonstrated that brain spectrin has the capability to interact with band 4.1 in a way which increases its ability to cross-link actin filaments.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 405-417 
    ISSN: 0886-1544
    Keywords: vinculin ; focal contacts ; microfilaments ; transformation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Talin is a recently identified cytoskeletal protein with a polypeptide molecular weight of 215,000 daltons. In cultured fibroblasts talin has been localized by immunofluorescence in adhesion plaques (focal contacts), in the ruffling membranes and leading lamellae of the cell periphery, and in fibrillar patterns that align with microfilament bundles and/or with cell surface fibronectin. These cellular locations suggest that the protein could function either in the attachment of microfilaments to the plasma membane or in the organization of microfilaments close to membrane attachment sites. Cell transformation by viruses such as Rous sarcoma virus disrupts the normal organization of talin, and in most transformed cells talin appears distributed diffusely through the cytoplasm. In a few cells talin is detected in doughnut-shaped aggregates, as a ring surrounding a central core of actin. The significance of these structures is uncertain, but in some cells the individual structures will condense to form much larger aggregates with a striking appearance when viewed by immunofluoresence microscopy.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 579-588 
    ISSN: 0886-1544
    Keywords: calcium-dependent protease ; contractile proteins ; platelets ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
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    Cell Motility and the Cytoskeleton 3 (1983), S. 623-633 
    ISSN: 0886-1544
    Keywords: spectrin ; ankyrin ; brain membranes ; spectrin subunits ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Further similarity between mammalian erythrocyte spectrin and pig brain spectrin has been demonstrated by (a) formation of hybrid molecules with brain α-chains and erythrocyte β-chains and by (b) identification of an ankyrin protein in brain membranes. Hybrid spectrin molecules prepared from brain α-chains and erythrocyte β-chains were visualized by low-angle rotary shadowing as double-stranded rods (dimers) 100 nM in length. 125I-labeled brain α-chain that was hybridized with erythrocyte β-subunit acquired ability to bind to ankyrin sites on erythrocyte membranes. 125I-labeled brain α-chain bound only to β-subunits of erythrocyte and brain spectrin following transfer of these polypeptides to nitrocellulose paper from sodium dodecyl sulfate (SDS) gels. Thus brain spectrin and mammalian erythrocyte spectrin have shared functional sites involved in association of their subunits. Additional evidence for similarity of brain and erythrocyte membranes is the finding of a 210,000 Mr membrane protein in brain that cross-reacts with erythrocyte ankyrin and has a water-soluble domain of 72,000 Mr that is produced by protease digestion. The 72,000 Mr domain of brain ankyrin has been isolated by affinity chromatography on erythrocyte spectrin-Sepharose, and was demonstrated to bind directly to erythrocyte and brain spectrin. The brain 72,000 Mr fragment has distinct peptide maps from the erythrocyte 72,000 Mr ankyrin fragment and thus is not a result of erythrocyte contamination.
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    Cell Motility and the Cytoskeleton 3 (1983), S. 671-682 
    ISSN: 0886-1544
    Keywords: actin ; cytoskeleton ; membrane connections ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Recently, molecules highly related to erythrocyte spectrin have been identified in nonerythroid cells. Here we summarize our current understanding of these molecules and suggest a model for their organization. Significant differences exist between this family of proteins isolated from mammalian cells and avian cells, and this may explain the variability in antibody preparations as well as differences in peptide maps of these subunits which have been reported. We have prepared antibodies specific for the variant subunits of the spectrinlike proteins fodrin, spectrin, and TW260/240 and analyzed the distribution of these variant subunits in different chicken cell types as well as their developmental distribution in the intestine. The results suggest that fodrin is the general member of this family of proteins and can even coexist with other spectrinlike proteins in the same cells.
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    Cell Motility and the Cytoskeleton 4 (1984), S. 431-441 
    ISSN: 0886-1544
    Keywords: dynein ; chromatophores ; permeabilization ; melanosomes ; motility ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Teleost chromatophores are filled with individual pigment granules that rapidly aggregate to the cell center or become dispersed throughout the cytoplasm in response to environmental stimuli. Microtubules appear to be required for pigment aggregation (movement toward the cell center), and recent findings have suggested that a dynein-like ATPase may participate in force production. Based on previous studies, however, it has been argued that pigment aggregation does not require energy directly, a view that supports the involvement of an elastic component in granule movement. To examine this point further, we have reinvestigated the energy requirements for pigment aggregation using both intact cells and detergent-permeabilized cell models of Fundulus melanophores. Poisons of oxidative phosphorylation, namely, 2,4 dinitrophenol and NaCN, reversibly inhibit melanosome aggregation in response to adrenaline. Inhibition of movement results directly from depletion of intracellular ATP, since pigment translocation can be reactivated in permeabilized cells by the addition of exogenous ATP to the lysis buffer. Non-hydrolyzable analogues, including β,γ-imidoadenosine-5′-triphosphate (AMPPNP), β,γ-methylene adenosine-5′-triphosphate (AMPPCP), and ATPγS, will not substitute for ATP in reactivation of movement. Similarly, other nucleotides such as ADP, AMP, GTP, CTP, and ITP, have limited ability to support melanosome aggregation in metabolically poisoned cells subjected to detergent lysis. ATP itself has no effect on intact cells. These results indicate that melanosome aggregation is ATP-dependent and energy-driven, and are consistent with a role for a force-transducing ATPase in particle movement.
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    Cell Motility and the Cytoskeleton 30 (1995), S. 1-7 
    ISSN: 0886-1544
    Keywords: actin ; cytoskeleton ; contractile ring ; microinjection ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Cofilin is a small actin-binding protein which reguiates actin polymerization in a pH-dependent manner. Immunofluorescence microscopy with a monoclonal antibody for cofilin revealed that this protein is temporarily concentrated at the contractile ring during cytokinesis. Cofilin appeared to accumulate rapidly at the contractile ring during late stages of furrowing, and was finally enriched at the midbody. The concentration of cofilin at the contractile ring was observed in several kinds of cultured cells. Furthermore, cofilin introduced into living cells by a microinjection method was also concentrated at the contractile ring. These results suggest that cofilin is involved in actin reorganization during cytokinesis. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 30 (1995), S. 38-49 
    ISSN: 0886-1544
    Keywords: Listeria monocytogenes ; actin ; profilin ; DNase I ; vitamin D-binding protein ; phalloidin ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Infection of host cells by Listeria monocytogenes results in the recruitment of cytoplasmic actin into a tail-like appendage that projects from one end of the bacterium. Each filamentous actin tail progressively lengthenes, providing the force which drives the bacterium in a forward direction through the cytoplasm and later results in Listeria cell-to-cell spread. Host cell actin monomers are incorporated into the filamentous actin tail at a discrete site, the bacterial-actin tail interface. We have studied the consequences of microinjecting three different actin monomer-binding proteins on the actin tail assembly and Listeria intracellular movement. Introduction of high concentrations of profilin (estimated injected intracellular concentration 11-22 m̈M) into infected PtK2 cells causes a marked slowing of actin tail elongation and bacterial migration. Lower intracellular concentrations of two other injected higher affinity monomer-sequenstering proteins, Vitamin D-binding protein (DBP; 1-2 m̈M) and DNase I (6-7 m̈M) completely block bacterial-induced actin assembly and bacterial migration. The onset of inhibition by each protein is gradual (10-20 min) indicating that the mechanisms by which these proteins interfere with Listeria-induced actin assembly are likely to be complex. To exclude the possibility that Listeria recruits preformed actin filaments to generate the tails and that these monomer-binding proteins act by depolymerizing such performed actin filaments, living infected cells have been injected with fluorescently labeled phalloidin (3 m̈M). Although the stress fibers are labeled, no fluorescent phalloidin is found in the tails of the moving bacteria. These results demonstrate that Listeria-induced actin assembly in PtK2 cells is the result of assembly of actin monomers into new filaments and that Listeria's ability to recruit polymerization competent monomeric actin is very sensitive to the introduction of exogenous actin monomer-binding proteins. © 1995 Wiley-Liss, Inc.
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    ISSN: 0886-1544
    Keywords: microfilamentous cytoskeleton ; actin binding proteins ; actin polymerization ; annealing ; non-muscle cells ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Gelsolin, a Ca++ activated, 90 kd actin binding protein, can regulate actin polymerization in polymorphonuclear leukocytes (PMNs) via severing of filaments to dissolve gels or by capping of filament ends to limit polymerization. In Triton-lysed PMNs, 30% of gelsolin is bound to the Triton-soluble F-actin (TSF) pool and none is bound to the Triton-insoluble F-actin (TIF) pool. Calcium-activated PMNs exhibit concurrent temporal and quantitative TIF growth and TSF and total F-actin loss. To determine if gelsolin plays a role in regulating TSF pool size, we monitored gelsolin-actin interactions and TIF, TSF and G-actin content at 5 second intervals in PMNs activated with the calcium ionophore, ionomycin. Actin pools were measured by NBDphallacidin binding and by gel scans and expressed relative to basal; gelsolin-actin interactions were measured as change in the amount of EGTA-resistant gelsolin:actin (G:A) complexes and by immunoblot quantification of gelsolin in actin pools. In basal PMNs, 33% of PMN gelsolin is bound in 1:1 EGTA-resistant G:A complexes and TSF and TIF retain 30% and 0% of PMN gelsolin, respectively. By 20 seconds after ionomycin addition, TSF decreases, TIF increases and a fraction of gelsolin repartitions from the TSF to the TIF pool. At maximum change (60 seconds), total F-actin (TIF + TSF) and TSF decrease and TIF increases by 25%; gelsolin is bound to both TSF and TIF (35% of total gelsolin in each pool), and 1:1 EGTA-resistant G:A complexes increase from 33% to 70%. No changes occur in cells activated by ionomycin in the absence of Ca++. The data show Ca++ activated TIF growth and TSF loss are temporally and quantitatively associated with an increase in the percent of gelsolin bound to actin and the translocation of gelsolin from TSF to TIF. This is unique, since no other PMN activator is known to repartition gelsolin into TIF actin. Further, the Ca++ activated initial increase in TIF concurrent with a fall in TSF without a change in total F-actin or G-actin content suggest that TIF grows initially only by TSF annealing/cross-linking to TIF. Gelsolin may regulate these events. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 30 (1995), S. 153-163 
    ISSN: 0886-1544
    Keywords: colchicine binding site ; MTC ; cod microtubules ; bovine microtubules ; MAPs ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Isolated microtubules from cod (Gadus morhua) are apparently more stable to colchicine than bovine microtubules. In order to further characterize this difference, the effect of the colchicine analogue 2-methoxy-5-(2,3,4-trimethoxyphenyl)-2,4,6-cyclo heptatrien-1-one (MTC) was studied on assembly, as measured by turbidity and sedimentation analysis, and on polymer morphology. MTC has the advantage to bind fast and reversible to the colchicine binding site of tubulin even at low temperatures. It was found to bind to one site in cod brain tubulin, with affinity (6.5 ± 1.5) × 105M 1at both low or high temperature, similarly to bovine brain tubulin. However, the effect of the binding differed. At substoichiometric concentrations of MTC bovine brain microtubule assembly was almost completely inhibited, while less effect was seen on the mass of polymerized cod microtubule proteins. A preformed bovine tubulin-colchicine complex inhibited the assembly of both cod and bovine microtubules at substoichiometric concentrations, but the effect on the assembly of cod microtubules was less. At higher concentrations (5 × 10-5 to 1 × 10-3M), MTC induced a large amount of cold-stable spirals of cod proteins, whereas abnormal polymers without any defined structure were formed from bovine proteins. Spirals of cod microtubule proteins were only formed in the presence of microtubule associated proteins (MAPs), indicating that the morphological effect of MTC can be modulated by MAPs. The effects of colchicine and MTC differed. At 10-5M colchicine no spirals were formed, while at 10-4M and 10-3M, a mixture of spirals and aggregates was found. The morphology of the spirals differed both from vinblastine spirals and from the spirals previously found when cod microtubule proteins polymerize in the presence of high Ca2concentrations. The present data show that even if the colchicine binding site is conserved between many different species, the bindings have different effects which seem to depend on intrinsic properties of the different tubulins. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 31 (1995), S. 34-44 
    ISSN: 0886-1544
    Keywords: microtubule ; MTOC ; mitosis ; MPM-2 ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: In diverse cell types, monoclonal antibody MPM-2 recognizes a class of phosphorylated proteins related to microtubule organizing centers and abundant during mitosis. We have used this antibody in an attempt to identify the spatial and temporal localization of putative microtubule organizing centers in endosperm cells of the higher plant Haemanthus. Our results show that MPM-2 recognized epitope is present in interphase cells and enriched in mitotic cells. In interphase the antibody usually stains cytoplasmic granules. During the interphase-prophase transition immunoreactive material appears in the nucleus, at the nuclear envelope, and in association with microtubules. Concomitantly, we observed an increase of immunoreactivity of the cytoplasm. During mitosis the phosphorproteins recognized by MPM-2 are detected in the cytoplasm, in association with microtubules of the spindle, the phragmoplast, and in the newly-formed cell plate. After completion of mitosis, only the cell plate and cytoplasmic granules are MPM-2 positive. Extraction of the cells with Triton X-100 prior to fixation removes staining of the cytoplasm by MPM-2. The detergent resistant immunoreactive material remains associated with surrounding the nucleus microtubules of the prophase spindle, the core of kinetochore fibers, and the phragmoplast. In the phragmoplast, however, segments of microtubules which are distal to the cell plate are depleted of MPM-2.These data demonstrate that microtubule arrays of endosperm cells are phosphorylated during mitosis. Thus, similar to animal cells, interphase and mitotic microtubules of higher plants have different properties. Additionally, the localization of detergent resistant MPM-2 antigen points to the difference in microtubule nucleation/organization between higher plant and animal cells.
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    Cell Motility and the Cytoskeleton 31 (1995), S. 59-65 
    ISSN: 0886-1544
    Keywords: flagella ; cane-shaped bend ; principal bend ; calcium ; membrane depolarization ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: To investigate the mechanism of the flagellar quiescence in sperm, we examined the effect of electric stimulation of individual spermatozoa of the sea urchin, Hemicentrotus pulcherrimus. Stimulation with a suction electrode attached to the sperm head elicited a flagellar quiescence response, in which the sperm showed a typical cane-shaped bend in the proximal region of the flagellum when the electrode was used as anode. Cathodic stimulation also induced quiescence, but was much less effective than anodic stimulation. During the quiescence response, which lasted for 1-3 s, no new bend was initiated, and subsequently the flagellum resumed normal beating. The quiescence response required the presence of Ca2+ (〉2 mM) in sea water, and was inhibited by Co2+ and La3+. At low Ca2+ concentrations (2-5 mM), the angle of the cane-shaped bend was smaller than that at 10 mM Ca2+; thus the angle of the cane-shaped bend, characteristic of the quiescence response is dependent on Ca2+ concentration. These results suggest membrane, followed by an influx of Ca2+ into the flagellum through Ca2+ channels. The increase in Ca2+ concentration within the flagellum affects the amount of sliding and thus produces a cane-shaped proximal bend of various angles, white inhibiting both the propagation of the proximal bend (principal bend) and the formation of a new reverse bend.
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    Cell Motility and the Cytoskeleton 30 (1995), S. 285-300 
    ISSN: 0886-1544
    Keywords: microtubule dynamics ; β-tubulin ; mitosis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Microtubule (MT) dynamics vary both spatially and temporally within cells and are thought to be important for proper MT cellular function. Because MT dynamics appear to be closely tied to the guanosine triphosphatase (GTPase) activity of β-tubulin subunits, we examined the importance of MT dynamics in the budding yeast S. cerevisiae by introducing a T107K point mutation into a region of the single β-tubulin gene, TUB2, known to affect the assembly-dependent GTPase activity of MTs in vitro. Analysis of MT dynamic behavior by video-enhanced differential interference contrast microscopy, revealed that T107K subunits slowed both the growth rates and catastrophic disassembly rates of individual MTs in vitro. In haploid cells tub2-T107K is lethal; but in tub2-T107K/tub2-590 heterozygotes the mutation is viable, dominant, and slows cell-cycle progression through mitosis, without causing wholesale disruption of cellular MTs. The correlation between the slower growing and shortening rates of MTs in vitro, and the slower mitosis in vivo suggests that MT dynamics are important in budding yeast and may regulate the rate of nuclear movement and segregation. The slower mitosis in mutant celis did not result in premature cytokinesis and cell death, further suggesting that cell-cycle control mechanisms “sense” the mitotic slowdown, possibly by monitoring MT dynamics directly. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 30 (1995), S. 310-323 
    ISSN: 0886-1544
    Keywords: mitosis ; mitotic apparatus ; sea urchin ; immunofluorescence ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: A protein component of 62-kDa (p62) in the mitotic apparatus of the sea urchin embryo has been shown to be important for the proper progression of mitosis [Dinsmore and Sloboda, 1989: Cell 57:127-134]. To study the subcellular distribution of p62 during the cell cycle of sea urchin embryos, indirect immunofluorescence microscopy was used coupled to a modified detergent extraction procedure. The improved fluorescent images obtained by this procedure provide new information concerning the subcellular localization of p62 during the cell cycle that could not be obtained with previous conventional staining procedures [Johnston and Sloboda, 1992: J. Cell Biol. 119:843-854]. Using affinity purified antibodies to p62, we observed a cell cycle-dependent localization of p62 to the chromosomes/chromatin. Prior to nuclear envelope breakdown of the first or second cell cycle, p62 localizes to chromatin in the nucleus. During mitosis, p62 associates with the region of the spindle occupied by the microtubules of the mitotic apparatus. As anaphase proceeds, but before the nuclear envelope reforms, p62 becomes progressively associated with the chromosomes. Thus, p62 is incorporated into the forming interphase nucleus due to its association with chromosomes during late anaphase, rather than by active translocation into the newly formed daughter nuclei through the nuclear pores. The protein is not unique to marine embryos, as demonstrated by immunofluorescence of Y-1 cells, a mouse adrenal tumor cell line In these cells, the localization of p62 is similar to the localization of the protein in echinoderm embryos, suggesting its possible function in mitotic progression in mammalian somatic cells as well. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 31 (1995), S. 45-58 
    ISSN: 0886-1544
    Keywords: colcemid ; kinesin ; actin ; topographic guidance ; micromachined substrata ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Fibroblats cultured on grooved substrata align themselves and migrate in the direction of the grooves, a phenomenon called contact guidance. Microtubules have been deemed important for cell polarization, directed locomotion, and contact guidance. Because microtubules were the first cytoskeletal element to align with the grooves when fibroblasts spread on grooved substrata, we investigated the consequences of eliminating the influence of microtubules by seeding fibro-blasts onto smooth and grooved micromachined substrata in the presence of colcemid. Fibroblasts were examined by time-lapse cinematography and epifluorescence or confocal microscopy to determine cell shape and orientation and the distribution of cytoskeletal or associated elements including actin filaments, vinculin, intermediate filaments, microtubules, and kinesin.As expected, cells spreading on smooth surfaces in the presence of colcemid did not polarize or locomote. Surprisingly however, by 24 hours, cells spread on grooves in the presence of colcemid were morphologically indistinguishable from controls spread on grooves. Both groups were aligned and polarized with the direction of the grooves and demonstrated directional locomotion along the grooves. In the absence of microtubules, kinesin localized to some of the aligned stress fibers and to leading edges of cells spreading on grooves. The grooved substratum compensated for the microtubule deficiency by organizing and maintaining an aligned actin filament framework. Thus, microtubules are not required to establish or maintain stable, polarized cell shapes or directed locomotion, provided an alternate oriented cytoskeletal component is available.
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    Cell Motility and the Cytoskeleton 31 (1995), S. 255-258 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 31 (1995), S. 207-214 
    ISSN: 0886-1544
    Keywords: flagella ; Chlamydomonas ; mutant ; high-frequency vibration ; nanometer-scale measurement ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The flageliar axoneme of the mutant pf18 lacking the central pair does not beat, but undergoes a nanometer-scale, high-frequency oscillation (hyper-oscillation) in the presence of ATP [Yagi et al., 1994: Cell Motil, Cytoskeleton 29:177-185]. The present study demonstrates that the amplitude of the hyper-oscillation increases significantly in the simultaneous presence of ATP and ADP. In addition, the hyper-oscillation under these conditions sometimes takes on an exceptionally simple asymmetric pattern, in which the maximal shearing velocity exceeds 50 μm/sec, much higher than the maximal velocity of ordinary dynein-microtubule sliding. The asymmetric oscillation thus appears to be at least partly driven by an internal elastic force. Its amplitude suggests that the axoneme has an elastic component that can be stretched by as long as 0.1 μm. Analyses of the asymmetric pattern further suggests that the axonemal dyneins have a tendency to attach to and detach from the doublets cooperatively and that the mechanochemical cycle of dynein has an inherent refractory period of about 2 msec, during which dynein cannot interact with microtubules.
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  • 75
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    Keywords: Ascaris sperm ; motility ; computer-assisted motion analysis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Computer-assisted methods have been employed to obtain a high resolution description of pseudopod expansion, cellular translocation, and the subcellular dynamics of MSP fiber complexes in the motile sperm of the nematode Ascaris suum. Although Ascaris sperm translocating in a straight line or along a curved path do not retract their pseudopod or significantly alter pseudopod shape, they move in a cyclic fashion, with an average period between velocity peaks of 0.35 × 0.05 min, which is independent of the forward velocity of sperm translocation. Expansion is confined to a central zone at the distal edge of the pseudopod for sperm translocating in a straight line and to a left-handed or right-handed lateral zone in the direction of turning, for sperm translocating along a curved path. For cells translocating in a straight line, the branch points and kinks of MSP fiber complexes move in a retrograde direction in relation to the substratum at an average velocity of 11 μm per min which is independent of the forward velocity of sperm translocation. The distal (anterior) end of a fiber complex, however, moves distally at the speed of sperm translocation when it emanates from the expansion zone, but when it is displaced to a nonexpanding surface of the pseudopod, it stops moving distally. When a cell is anchored to the substratum and is, therefore, nonmotile, the velocity of fiber complexes moving in a retrograde direction doubles. The unique aspects of pseudopod and MSP fiber complex dynamics in Ascaris are compared to the dynamics of pseudopod formation and actin filament dynamics in traditional actin-based amoeboid cells, and the treadmill model for MSP polymerization is reassessed in light of the discovery that fiber complex branch points move proximally (posteriorly) at a fixed rate.
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    Cell Motility and the Cytoskeleton 31 (1995), S. 323-332 
    ISSN: 0886-1544
    Keywords: adherens junction ; cytoskeleton ; intercellular junction ; tight junction ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We previously reported the expression of ZO-1 in cell types that do not form tight junctions. Here we compare the molecular environments of ZO-1 in epithelial cells, primary cultures of astrocytes and in the non-epithelial S180 sarcoma cell line. ZO-1 co-localizes with a subset of actin filament in all cell types. In astrocytes, ZO-1 is found concentrated in discrete bands at points of cell-cell contact. Indirect immunofluorescent microscopy shows that these bands of ZO-1 co-localize with the adherens junction proteins vinculin and α-actinin, and with the antigen recognized by a pan-cadherin antibody. In contrast, ZO-1 in S180 cells, which exhibit limited cell-cell interactions, is diffusely distributed over the plasma membrane, with concentrations in lamellipodia where actin filaments accumulate. ZO-1 does not co-localize with vinculin at focal adhesions in this cell type. Analysis of ZO-1 immunoprecipitation profiles from different cell types, performed under conditions previously demonstrated to maintain interactions between ZO-1, ZO-2 and p130 from the MDCK epithelial cell line, show that the proteins which co-precipitate with ZO-1 vary with cell type. Precipitation of polypeptides at 165 kDa, potentially ZO-2, and 65 kDa occurs in both a mouse kidney tubule epithelial cell line and the non-epithelial S180 cells. No proteins specifically associate with ZO-1 immunoprecipitated from astrocytes. Spectrin, α-actinin, vinculin and cadherin are not detected in immunoblots of ZO-1 immunoprecipitates from any cell type. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 32 (1995), S. 26-36 
    ISSN: 0886-1544
    Keywords: microtubules ; motor proteins ; axonal transport ; mitosis ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We report the cloning and sequencing of genomic DNA encoding a cytoplasmic dynein heavy chain from the nematode Caenorhabditis elegans. In a contiguous stretch of 35,103 bp of DNA from the left arm of linkage group I, we have found a gene that is predicted to encode a protein of 4,568 amino acids. This gene is composed of 15 exons and 14 relatively short introns, and it has significant homology of the other dynein heavy chains in the databases. The deduced molecular mass of the derived polypeptide is 512,624 Da. As with other dynein heavy chains that have been sequenced to date, it contains four GXXGXGK(S/T) motifs that form part of the consensus sequence for nucleotide triphosphate-binding domains. Comparison of axonemal and cytoplasmic dynein heavy chains shows that regions of homology among all dyneins are clustered in the carboxyl terminal two-thirds of the polypeptide, whereas the amino terminal one-third of the heavy chains may contain domains that specify functions that differ between axonemal and cytoplasmic forms of the dynein heavy chain. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 32 (1995) 
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    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 32 (1995), S. 95-97 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 32 (1995), S. 106-109 
    ISSN: 0886-1544
    Keywords: Chlamydomonas ; cilia and flagella ; protein kinase and phosphatase ; dynein-driven microtubule sliding ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The following is a summary of physiological and pharmacological studies of the regulation of dynein-driven microtubule sliding in Chlamydomonas flagella. The experimental basis for the study is described, and data indicating that an axonemal cAMP-dependent protein kinase can regulate inner arm dynein activity are reviewed. In addition, preliminary data are summarized indicating that an axonemal type 1 phosphatase can also regulate dynein-drive microtubule sliding velocity. It is predicted that the protein kinase, phosphatase, and an inner dynein arm component form a regulatory complex in the axoneme.
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    Cell Motility and the Cytoskeleton 32 (1995), S. 129-132 
    ISSN: 0886-1544
    Keywords: Life and Medical Sciences ; Cell & Developmental Biology
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    Cell Motility and the Cytoskeleton 32 (1995), S. 151-161 
    ISSN: 0886-1544
    Keywords: membrane localization ; ATPase activity ; actin binding ; calmodulin ; motility ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Although the specific functions of myosin I motors are not known, their localization to membrane structures suggests a function in membrane motility. Different myosin I isoforms in the same cell or in different cells can possess different localizations. To determine if the localization and biochemical activity of the best-characterized mammalian myosin I, chicken intestinal epithelium brush border myosin I, was dependent on determinants of the membrane or actin cytoskeleton specific to epithelial cells, we transfected the cDNA for the heavy chain of this myosin into COS cells. Transient transfection of COS cells with the chicken brush border myosin I heavy chain resulted in the production of recombinant myosin I. Recombinant brush border myosin I localized to protrusions of the plasma membrane, particularly at spreading cell edges, and also to unknown cytoplasmic structures. Some cells expressing particularly high levels of brush border myosin I possessed a highly irregular surface. Recombinant brush border myosin I purified from COS cells bound to actin filaments in an ATP-dependent manner and decorated actin filaments to form a characteristic appearance. The recombinant myosin also catalyzed calcium-sensitive, actin-activated MgATPase activity similar to that of the native enzyme. Thus, any cellular factor required for the general membrane localization or biochemical activity of brush border myosin I is present in COS cells as well as intestinal epithelium.
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    Cell Motility and the Cytoskeleton 32 (1995), S. 1-9 
    ISSN: 0886-1544
    Keywords: review ; fascin ; actin ; actin bundling proteins ; filopodia ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Fascin is an actin-bundling protein that was first isolated from cytoplasmic extracts of sea urchin eggs [Kane, 1975: J. Cell Biol. 66:305-315] and was the first bundling protein to be charactrized in vitro. Subsequent work has shown that fascin bundles actin filaments in fertilized egg microvilli and filopodia of phagocytic coelomocytes [Otto et al., 1980: Cell Motil. 1:31-40; Otto and Bryan, 1981: Cell Motil. 1:179-192]. Fifteen years later, the molecular cloning of sea urchin fascin [Bryan et al., 1993: Proc. Natl. Acad. Sci. U.S.A. 90:9115-9119] has led to the identification and characterization of homologous proteins in Drosophila [Cant et al., 1994: J. Cell Biol. 125:369-380], Xenopus [Holthuis et al., 1994: Biochim. Biophys. Acta. 1219:184-188], rodents [Edwards et al., 1995: J. Biol. Chem. 270:10764-10770], and humans [Duh et al., 1994: DNA Cell Biol. 13:821-827; Mosialos et al., 1994: J. Virol. 68:7320-7328] that bundle actin filaments into structures which stabilize cellular processes ranging from mechanosensory bristles to the filopodia of nerve growth cones. Fascin has emerged from relative obscurity as an exotic invertebrate egg protein to being recognized as a widely expressed protein found in a broad spectrum of tissues and organisms. This purpose of this review is to relate the early studies done on sea urchin and HeLa cell fascins to the recent molecular biology that defines a family of bundling proteins, and discuss the current state of knowledge regarding fascin structure and function. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 32 (1995), S. 173-186 
    ISSN: 0886-1544
    Keywords: microtubule dynamics ; microinjection ; centripetal transport ; pinocytotic vesicles ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: The Study of microtubule (MT) dynamics in cells has largely been restricted to events occurring over relatively short periods in nonmotile or stationary cell in culture. By using the antioxidant, Oxyrase, we have reduced the sensitivity of fluorescent MTs to photodamage and this has allowed us to image fluorescent MTs with good temporal resolution over much longer periods of time. We have used our enhanced imaging capabilities to examine MT dynamics in fibroblasts moving directionally into a wound. We found that MTs in these cells exhibited dynamic instability similar to that reported for other cells. More interestingly, we found a novel dynamic behavior of the MTs in wihch entire MTs were moved inward from the leading edge toward the cell nucleus. This centripetal transport (CT) of MTs only occurred to those MTs that were oriented with their long axis parallel to the leading edge; radially oriented MTs were not transported centripetally. Both small bundles of MTs and individual MTs were observed to undergo CT at a rate of 0.63 × 0.37 μm/min. This rate was similar to the rate of CT of latex beads applied to the cell surface and of endogenous pinocytotic vesicles in the cytoplasm. When we imaged both MTs and pinocytotic vesicles, we found that the pinocytotic vesicles were ensheathed by a small group of parallel MTs that moved centripetally in concert with the vesicles. Conversely, we found many instances of MTs moving centripetally without associated vesicles. When cells were treated with nocodazole to depolymerize MTs rapidly, the rate of pinocytotic vesicle CT was inhibited by 75%. This suggests that centripetal transport of MTs may be involved in the movement of pinocytotic vesicles in cells. In conclusion, our results show that MTs in motile cells are redistributed by a novel mechanism, CT, that does not require changes in polymer length. The centripetally transported MTs may play a role in transporting pinocytotic vesicles in the cell. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 32 (1995), S. 233-243 
    ISSN: 0886-1544
    Keywords: caldesmon ; over-expression ; cell cycle ; motility ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Caldesmon is an actin, calmodulin, tropomyosin, and myosin binding protein implicated in the regulation of actomyosin interactions. We have invesigated the effect of overexpression of the higher molecular weight smooth muscle isoform of caldesmon on mouse L cell physiology. Mouse L(TK-) cell were transfected stably with plasmids carrying the TK+ gene and a full length human smooth muscle caldesmon cDNA under control of the adenovirus major late promoter. Two clones displaying four and eight times the level of the endogenous mouse high molecular weight caldesmon were isolated. These cells acquire a distinct phenotype characterized by an altered morphology, including an increased number of processes and larger area due to enhanced cell spreading, and a significantly slower growth rate than that of untransfected control cells, or cells transfected with the TK+ gene alone. The majority of the overexpressed caldesmon appears to be active and localized on cytoskeleton structures as determined by detergent lysis. Immuno-fluorescence analysis of the clones revealed that the caldesmon is localized as punctate staining on stress-fibers and in membrane ruffles. The immunofluores-cence images suggest that caldesmon overexpressing cells have more total filaments than control cells. The effects of excess caldesmon on cell mobility are ambiguous: one clone displayed increased motility compared to the control, while the motility of the second clone was decreased relative to the control. © 1995 Wiley-Liss, Inc.
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    Cell Motility and the Cytoskeleton 32 (1995), S. 289-298 
    ISSN: 0886-1544
    Keywords: cytoskeleton ; intermediate filaments ; vimentin ; microtubules ; myoepithelial cells ; immunofluorescence ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Salivary gland neoplastic myoepithelial cells in culture form very thin cytoplasmic processes in which the vimentin network is well dispersed. These vimentin filaments can be individually visualized by immunofluorescence. In this study, we have analyzed the role of microtubules in the distension and organization of the vimentin filament network found in these cells. We find that vimentin filaments colocalize along microtubules; however, a significant number of filaments can also be found in microtubule-free domains. Additionally, vimentin filaments are absent from large domains of microtubule inhibitor nocodazole did not cause any retraction of the distended vimentin network. This observation suggests that the structural integrity of microtubules is not important for the stability of the vimentin network. Combining procedures for transient disruption of vimentin filaments and microtubules we observed that, in the absence of microtubules, the vimentin network could reassemble in the perinuclear region but was unable to extend toward the cell periphery. The dispersion of vimentin filaments to the peripheral regions of the cytoplasm could only be observed upon microtubule reassembly. This indicates that microtubules are not required for the stability of the vimentin network, but the dispersion of vimentin filaments to the peripheral cytoplasm depends on active interactions with microtubules. © 1995 Wiley-Liss, Inc.
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    Journal of Chemometrics 9 (1995), S. 197-209 
    ISSN: 0886-9383
    Keywords: proficiency test ; true value ; homogeneity robust statistic ; standard ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Profficiency tests raise two types of problems: (i) the homogeneity of a sample must be carefully checked before using it as a reference material; (ii) it is necessary to define a conventional reference value (RV) in order to rank participants. Since these topics are poorly addressed in the literature, a reference material was specially prepared in order to propose a procedure for verifying homogeneity and to establish whether the algorithms classically used to compute the conventional true value have an influence on the conclusion of the test.The homogeneity of the sample was not perfect and univariate and multivariate techniques were used to demonstrate some analytes can be suspected as heterogeneous. However, this was considered adequate for introducing the sample in a large proficiency test organized between four laboratory associations which regularly perform such tests. Altogether more than 3000 measurements were collected and eight algorithms were applied to compute the RV on 14 analytes. Thus is was possible to demonstrate that some of these algorithms are better adapted than others. It is also obvious that some analytes are better suited to proficiency testing.It can be concluded from this work that some effort towards standardization would be profitable to check homogeneity or to compute the RV, especially since the economic weight of proficiency testing is becoming even more important with the development of certification accreditation.
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    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
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    Journal of Chemometrics 9 (1995), S. 451-457 
    ISSN: 0886-9383
    Keywords: non-linear regression ; optimization ; robust methods ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: Several robust regression methods, including a new proposal, are described and their properties discussed. Resistance to various types of outliers and non-normality is demonstrated. The techniques are applied to non-linear regression models from chemical kinetics and calibration. Optimization of the types of objective functions encountered when applying robust regression is considered.
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    Journal of Chemometrics 9 (1995), S. 471-481 
    ISSN: 0886-9383
    Keywords: batch prediction ; continuum regression ; multivariate calibration ; sequential prediction ; simultaneous prediction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: In analytical chemistry a single fitted calibration model is used repeatedly to predict the level of the analyte of interest for the specimens comprising the prediction set. Unlike the calibration (or training) set, which is often limited in size, the prediction set can be very large.In the case of multivariate calibration a number of methods such as PLS and PCR are commonly used to construct the calibration model. The set of instrumental measurements and the reference analyte level are available for each specimen in the calibration set. For specimens in the prediction set, only the instrumental measurements are available, since the problem is to predict the analyte level for these specimens. It is not widely recognized that predictions of the analyte levels for individual specimens can be improved by utilizing seemingly unrelated information from the instrumental measurements associated with the other members of the prediction set. In the case of PCR there exists a very straightforward procedure for doing this. A description of the various sources of prediction errors is provided to explain the ability of PCR to utilize this additional information. The use of PCR in this context is illustrated with both a synthetic and a real example.
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    Journal of Chemometrics 9 (1995), S. 21-29 
    ISSN: 0886-9383
    Keywords: Near-infrared absorbance ; Partial least squares ; Principal component regression ; Root-mean-square error of prediction ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The use of principal component regression (PCR) as a multivariate calibration method has been discussed by a number of authors. In most situations principal components are included in the regression model in sequence based on the variances of the components, and the principal components with small variances are rarely used in regression. As pointed out by some authors, a low variance for a component does not necessarily imply that the corresponding component is unimportant, especially when prediction is of primary interest. In this paper we investigate a different version of PCR, correlation principal component regression (CPCR). In CPCR the importance of principal components in terms of predicting the response variable is used as a basis for the inclusion of principal components in the regression model. Two typical examples arising from calibrating near-infrared (NIR) instruments are discussed for the comparison of the two different versions of PCR along with partial least squares (PLS), a commonly used regression approach in NIR analysis. In both examples the three methods show similar optimal prediction ability, but CPCR performs better than standard PCR and PLS in terms of the number of components needed to achieve the optimal prediction ability. Similar results are also seen in other NIR examples.
    Additional Material: 2 Ill.
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  • 93
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    Journal of Chemometrics 9 (1995), S. i 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 94
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    Journal of Chemometrics 9 (1995), S. 137-138 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 95
    ISSN: 0886-9383
    Keywords: pattern recognition ; infrared spectra ; factor analysis ; maximum likelihood method ; entropy of information ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The spectral region from 700 to 3600 cm-1 is subdivided into several wave number intervals. The peaks in each interval are summarized by means of three encoding algorithms. Using a factor model of kcommon factors, the total extractable variacnce (com) of a given set of intervals is calculated and correlated with the redundancy of information in all these intervals. The value of com is verified by analysis of the factor loadings aik (factor pattern). Finally, the information content of some chosen sets of intervals coded by the three selected feature algorithms will be correlated to the probability of information flow through a serial-parallel network. The encoding using only wave numbers was found to be the most effective.
    Additional Material: 9 Ill.
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  • 96
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    Journal of Chemometrics 9 (1995), S. 211-221 
    ISSN: 0886-9383
    Keywords: diagnostics statistics ; QSAR ; MASCA ; principal component regression ; non-least squares regression ; types of multicollincarity ; flagged observations ; influential points ; high-leverage points ; outliers ; extra-carrier points ; random perturbation ; cluster correalation ; resampling ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The formal application of a Hansch analysis to a series of 3-quinuclidinyl benzylates (QNBs) led to a ‘statistically significant’ QSAR equation. In contrast, the application of the MASCA model has shown that the design matrix is unsuitable for each QSAR analysis: one sample member is an outlier but not a high-leverage or influential point; another one is an influential point, a high-leverage point and an extra-carrier point. The regressors of the design matrix are multicollinear without predictive model power. The result of such flagged observation and this type of multicollinearity is a multiple cluster correlation. The QNB series is a good example for ‘sampling artifacts’ where no practically important but artificial QSARs can be found.
    Additional Material: 3 Ill.
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  • 97
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    Journal of Chemometrics 9 (1995), S. 230-231 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
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  • 98
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995), S. 239-262 
    ISSN: 0886-9383
    Keywords: industrial experimentation ; parameter design ; quality by design ; robust design ; Taguchi method ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: The aim of this paper is to present a simple structured review of the different approaches to robust process design to clarify their similarities and dissimilarities. It is primarily written for practitioners who wish to understand and compare the main ideas of each approach and to apply them to their work. Two examples are used to illustrate the different approaches and their corresponding data analysis strategies: the first one is a constructed example on a pigment kneading process and the second one is real example dealing with the validation of an HPLC method. A comparison of the different approaches is provided and some practical recommendations are formulated.
    Additional Material: 12 Ill.
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  • 99
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    Journal of Chemometrics 9 (1995), S. 323-326 
    ISSN: 0886-9383
    Keywords: partial least squares ; biased regression ; ordinary least squares ; minimum length least squares ; Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Notes: An algebraic proof is given that in partial least squares (PLS) regression the Euclidean length of the estimator is shrunk in comparison with the ordinary least squares estimator or with PLS estimators based on a larger number of dimensions.
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  • 100
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    New York, NY : Wiley-Blackwell
    Journal of Chemometrics 9 (1995) 
    ISSN: 0886-9383
    Keywords: Chemistry ; Analytical Chemistry and Spectroscopy
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Chemistry and Pharmacology
    Type of Medium: Electronic Resource
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