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  • 1
    Electronic Resource
    Electronic Resource
    Heterochronic differences of Hoxa-11 expression in Xenopus fore- and hind limb development: Evidence for lower limb identity of the anuran ankle bones (1998)
    Springer
    Development genes and evolution 208 (1998), S. 175-187 
    Details
    ISSN: 1432-041X
    Keywords: Key words Limb development ; Heterochrony ; Evolutionary innovation ; Hoxa-11 ; Xenopus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The wrist (carpus) and ankle (tarsus) of most tetrapods, as well as the wrist of anurans, contains relatively small nodular skeletal elements. The anuran tarsus, however, comprises a pair of long bones, the proximal tarsals tibiale and fibulare, which resemble the lower leg bones, tibia and fibula (zeugopodium). In this paper we investigate whether the proximal tarsals of Xenopus are of zeugopodial character identity, i.e. whether they develop under the influence of the same genes that pattern the lower limb. We compare Hoxa-11 expression in the forelimb bud with that in the hind limb bud by whole-mount in situ hybridization. Hoxa-11 has been implicated in the development of the lower limb. In Xenopus we note three differences between Hoxa-11 expression in fore- and hind limb buds: (1) Hoxa-11 expression is maintained until the hind limb bud reaches a larger size (2 mm) than that of the forelimb bud (1.5 mm); (2) Hoxa-11 expression is maintained over larger spatial domains than in the forelimb; and (3) Hoxa-11 expression has a pronounced posterior polarity in the hind limb, but not in the forelimb. Hind limb expression of Hoxa-11 can be understood as a heterochronic prolonging of the expression dynamic in the forelimb. Finally we found that the proximal tarsals start to develop within the expression domain of Hoxa-11, while in the forelimb the lower arm elements reach the distal expression limit of Hoxa-11. The gene expression data presented here support the notion of a zeugopodial identity of the proximal tarsal elements in Xenopus.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050172
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  • 2
    Electronic Resource
    Electronic Resource
    A recombinogenic targeting method to modify large-inserts for cis-regulatory analysis in transgenic mice: construction and expression of a 100-kb, zebrafish Hoxa-11b-lacZ reporter gene (2000)
    Springer
    Development genes and evolution 210 (2000), S. 105-109 
    Details
    ISSN: 1432-041X
    Keywords: Key words Cis-regulatory sequences ; P1/PAC clones ; Homologous recombination ; Reporter gene ; AbDb-like Hox genes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract  The identification of cis-sequences responsible for spatiotemporal patterns of gene expression often requires the functional analysis of large genomic regions. In this study a 100-kb zebrafish Hoxa-11b-lacZ reporter gene was constructed and expressed in transgenic mice. PAC clone 10-O19, containing a portion of the zebrafish HoxA-b cluster, was captured into the yeast-bacterial shuttle vector, pPAC-ResQ, by recombinogenic targeting. A lacZ reporter gene was then inserted in-frame into exon 1 of the zfHoxa-11b locus by a second round of recombinogenic targeting. Expression of the zfHoxa-11b-lacZ reporter gene in 10.5 d.p.f. transgenic mouse embryos was observed only in the posterior portion of the A-P axis, in the paraxial mesoderm, neural tube, and somites. These findings demonstrate the utility of recombinogenic targeting for the modification and expression of large inserts captured from P1/PAC clones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004270050016
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  • 3
    Electronic Resource
    Electronic Resource
    Anti-noradrenergic drugs do not interfere with the development of callosal connections in the rat (1982)
    Springer
    Cellular and molecular life sciences 38 (1982), S. 1218-1219 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary When noradrenergic transmission was suppressed by 6-OHDA, propranolol or phentolamine callosal fibers developed the same innervation pattern as in normal rats and the density of callosal connections did not increase.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01959749
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  • 4
    Electronic Resource
    Electronic Resource
    Self-stabilization of neuronal networks (1986)
    Springer
    Biological cybernetics 54 (1986), S. 211-222 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract Between the extreme views concerning ontogenesis (genetic vs. environmental determination), we use a moderate approach: a somehow pre-established neuronal model network reacts to activity deviations (reflecting input to be compensated), and stabilizes itself during a complex feed-back process. Morphogenesis is based on an algorithm formalizing the compensation theory of synaptogenesis (Wolff and Wagner 1983). This algorithm is applied to randomly connected McCulloch-Pitts networks that are able to maintain oscillations of their activity patterns over time. The algorithm can lead to networks which are morphogenetically stable but preserve self-maintained oscillations in activity. This is in contrast to most of the current models of synaptogenesis and synaptic modification based on Hebbian rules of plasticity. Hebbian networks are morphogenetically unstable without additional assumptions. The effects of compensation on structural and functional properties of the networks are described. It is concluded that the compensation theory of synaptogenesis can account for the development of morphogenetically stable neuronal networks out of randomly connected networks via selective stabilization and elimination of synapses. The logic of the compensation algorithm is based on experimental results. The present paper shows that the compensation theory can not only predict the behavior of synaptic populations (Wagner and Wolff, in preparation), but it can also describe the behavior of neurons interconnected in a network, with the resulting additional system properties. The neuronal interactions-leading to equilibrium in certain cases-are a self-organizing process in the sense that all decisions are performed on the individual cell level without knowing the overall network situation or goal.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00318417
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  • 5
    Electronic Resource
    Electronic Resource
    Self-stabilization of neuronal networks (1988)
    Springer
    Biological cybernetics 58 (1988), S. 149-158 
    Details
    ISSN: 1432-0770
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Computer Science , Physics
    Notes: Abstract This study is concerned with synaptic reorganization in local neuronal networks. Within networks of 30 neurons, an initial disequilibrium in connectivity has to be compensated by reorganization of synapses. Such plasticity is not a genetically determined process, but depends on results of neuronal interaction. Neurobiological experiments have lead to a model of the behavior of individual neurons during neuroplastic reorganization, formalized as a “synaptogenetic rule” that governs changes in the amount of synaptic elements on each neuron. — When this synaptogenetic rule is applied to a system of neurons, there is some freedom left to the choice of further conditions. In this study it is examined, which assumptions additional to the synaptogenetic rule are essential in order to obtain morphogenetic stability. By explicating these assumptions, their plausibility can be tested. It is analysed, in which respect these conditions are important, in which part of the model they exert their influence, and what kind of instability and degeneration happens if the assumptions are violated. —Our essentials for reaching morphogenetic stability are: (1) A network structure that guarantees the possibility of oscillations, (2) a compensation algorithm that guarantees a smooth morphogenesis, (3) kinetic parameters that guarantee convergence in the synaptic elements' change, and (4) a synaptic modification rule that prohibits Hebb-like as well as anti-Hebb-like synaptic changes. — It is concluded that many structural features of the mammalian cerebral cortex are in accordance with the requirements of the model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00364134
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  • 6
    Electronic Resource
    Electronic Resource
    Micro-anatomy of the pectoral fin in blennies (Blenniini, Blennioidea, Teleostei) (1990)
    Oxford, UK : Blackwell Publishing Ltd
    Journal of fish biology 37 (1990), S. 0 
    Details
    ISSN: 1095-8649
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Blennioid fishes show a highly differentiated pectoral fin, which they use to cling to the substrate. The lower part of the pectoralis, comprising about four to six fin rays, forms a hook-field with specific anatomical features: (1) the rim of the fin web has a saw-like appearance, because it extends from the tip of a fin ray to the shaft ofthe upper of two neighbouring fin rays, (2) the outer half of the bony fin ray carries a lepidotrichal cord composed of fibrocytes, collagen, elastic fibres and acidic GAGS, (3) the epidermis overlying the lepidotrichal cord is differentiated in terms of cyto-architecture and forms a conspicuous cuticle. The upper part of the pectoral fin does not show any obvious specializations and is used for swimming and undulation. The vascularization of the fin originates from a stem vessel which gives rise to five branches, each supplying two or three neighbouring fin rays. Each fin ray is accompanied by a single arterial vessel at its upper edge. No vessels are found in the space between the bony fin ray halves. The morphology of the shoulder girdle and pectoral fin shows only little variation among the four species of Blenniini studied. Most remarkable is the fusion of the coracoid with the cleithrum, loss of one element of the suspensorium and the absence of branched fin rays. The possible relevance of the Blennioid pectoral fin as a model for the origin of morphological novelties in connection with functional specializations is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1095-8649.1990.tb02537.x
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  • 7
    Electronic Resource
    Electronic Resource
    The Biological Homology Concept (1989)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 20 (1989), S. 51-69 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.20.110189.000411
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  • 8
    Electronic Resource
    Electronic Resource
    Novelty in Evolution: Restructuring the Concept (1991)
    Palo Alto, Calif. : Annual Reviews
    Annual Review of Ecology, Evolution, and Systematics 22 (1991), S. 229-256 
    Details
    ISSN: 0066-4162
    Source: Annual Reviews Electronic Back Volume Collection 1932-2001ff
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1146/annurev.es.22.110191.001305
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  • 9
    Electronic Resource
    Electronic Resource
    The oxidation of cobalt based alloys containing partially dissolved particles of Si3N4 at 1000°C (1987)
    Springer
    Oxidation of metals 27 (1987), S. 157-176 
    Details
    ISSN: 1573-4889
    Keywords: high temperature oxidation ; dispersion of Si3N4 ; cobalt base alloys ; Cr2O3 and SiO2
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract The isothermal oxidation behavior of Co-Cr and Co-Cr-Si alloys with and without 5, 10, and 15 vol.% dispersions of unstable Si3N4 particles was studied in 1 atm of oxygen at 1000°C. The dispersion of Si3N4 which dissolved partially in the matrix, greatly reduced the oxidation rate of Co-Cr alloys. Silicon nitride was found to promote the formation of continuous Cr2O3 layers at low chromium concentrations. Furthermore, the unstable Si3N4 was more effective in reducing the oxidation rate than an alloy containing an equivalent amount of silicon. Additions of 15vol.% Si3N4 tended to increase the oxidation rate by forming nonprotective SiO2 particles which disrupted the protective Cr2O3 scale. The mechanism of oxidation was altered due to the Si3N4 additions. Marker experiments indicated oxygen diffusion inward via the CoO lattice, rather than a combination of both oxygen and metal ion motion which is encountered in Co-Cr alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00667056
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  • 10
    Electronic Resource
    Electronic Resource
    The oxidation of cobalt-chromium-titanium alloys at 1000°C (1986)
    Springer
    Oxidation of metals 26 (1986), S. 139-155 
    Details
    ISSN: 1573-4889
    Keywords: oxidation ; Co-Cr-Ti alloys ; kinetics ; scale morphology
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Notes: Abstract Cobalt-based alloys containing 3,5,10,15, and 20% Cr with 1 and 3% Ti were oxidized at 1000°C in slowly flowing oxygen gas. In general, titanium additions decreased the oxidation rate with the most pronounced effect being observed at the 10% Cr level. Titanium accelerated the formation of Cr2O3 layers at the metal-oxide interface. Faceted CrxTiyOz spinel particles were found at the metal-oxide interface which varied in composition according to microprobe results. There was no evidence of spalling on the Co-Cr-Ti alloys studied in contrast to the severe spalling normally encountered in Ni-Cr-Ti alloys. Distinct morphological differences existed on the outer CoO layer of the 1% Ti alloys in comparison to the O and 3% Ti alloys.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00664278
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