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  • 1
    Electronic Resource
    Electronic Resource
    The formation of the mesoderm in urodelean amphibians (1972)
    Springer
    Development genes and evolution 169 (1972), S. 185-199 
    Details
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Xenoplastic recombinations of animal and vegetative parts ofAmbystoma mexicanum and Triturus alpestris blastulae, and similar recombinations of parts of3H-thymidinelabelled and unlabelledAmbystoma mexicanum blastulae demonstrate convincingly that the vegetative part (zone IV, see Nieuwkoop, 1969a) of such a recombinate does not contribute to mesoderm formation, but exclusively forms endodermal derivatives. In contrast, the animal cap of the blastula (zones I.II)—which only gives rise to atypical ectoderm if isolated—not only furnishesall the ecto-neurodermal derivatives, butall the mesodermal structures of the developing recombinate as well, and finally to a varying extent forms additional endodermal structures in the recombinate. In the recombinates endodermization of the ectodermal cap occurred at the anterior end of the invaginated archenteron—corresponding to the presumptive pharyngeal endoderm —, and along the dorsal side of the endodermal tube, while an endoderm-like epithelium is formed at the boundary between the caudal endoderm and the ectoderm (proctodaeum formation). These results suggest that in normal development also endodermization occurs in the “ectodermal half” of the egg. This occurs particularly on the dorsal side, leading to the formation of the presumptive pharyngeal endoderm situated above the dorsal blastoporal groove. These experiments show that the vegetative “half” of the amphibian blastula is firmly determined as the future endoderm, whereas the animal “half” is still virtually undetermined and pluripotent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00582552
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  • 2
    Electronic Resource
    Electronic Resource
    Establishment of polarities in the oocyte of Xenopus laevis: the provisional axial symmetry of the full-grown oocyte of Xenopus laevis (1997)
    Springer
    Cellular and molecular life sciences 53 (1997), S. 382-409 
    Details
    ISSN: 1420-9071
    Keywords: Key words. Anurans; Xenopus laevis; symmetrization; axis formation; localizations; dorso-ventral; gravity; microgravity; space shuttle; clinostate.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. We aimed at understanding of formation and function of the 'Nieuwkoop Centre' in embryonic pattern formation. Discussed are data on genesis of cytoplasmic localizations in ovarian oocytes, transient modifications of cytoskeletal structures creating cytoplasmic asymmetries in fertilized eggs, the axis determining "vegetal cortical rotation" and fate of distinct cells, as shown by injection of specific molecular markers into particular blastomeres at specific times. Egg rotation and centrifugation suggested that sperm that gravity cooperate in symmetrization of the axially symmetrical anuran egg. After fertilization in space or in a fast rotating clinostate, axis formation and embryonic development were normal although the blastocoel was transiently abnormal. Normal tadpoles came back on Earth after ovulation, fertilization and culture in space. They metamorphosed normally and got healthy Earth-born F1 offspring. We conclude that neither sperm nor gravity are required for determination of the bilateral symmetry in the embryo of Xenopus laevis. In normal development sperm and gravity, either alone or in collaboration, may overrule an initial bilaterality inherent to the full-grown oocyte, residing in some still unidentified component(s)/or mechanisms.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/PL00000613
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  • 3
    Electronic Resource
    Electronic Resource
    La question des hétérochromosomes chez les Sauropsidés. Oiseaux (1956)
    Springer
    Cellular and molecular life sciences 12 (1956), S. 162-164 
    Details
    ISSN: 1420-9071
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary The chromosomes of the fowl were studied with the aid ofMakino's andNishimura's water pretreatment squash technique, modified byMatthey, in embryonic spleen and gonads of both sexes. The number of chromosomes was found to be about 78; the numerical variations are to be ascribed to technical difficulties, caused by the extremely small size of the microchromosomes, rather than to an unchromosomelike behaviour of the latter, as was supposed byNewcomer andBrant. As to the exact number of chromosomes, we consider its determination beyond the possibilities of cytology. The 5th largest pair of the male, represented by a single element in the female, could be identified as the sex chromosome pair, in accordance with the findings ofYamashina. The digamety might be of theZ-O orZ-W type.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02170616
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  • 4
    Electronic Resource
    Electronic Resource
    An immunocytochemical method for the visualization of tubulin-containing structures in the egg of Xenopus laevis (1982)
    Springer
    Histochemistry and cell biology 76 (1982), S. 527-538 
    Details
    ISSN: 1432-119X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Summary Tubulin can be isolated and purified from Xenopus laevis egges through modification of Olmstedt's (1970) tubulin isolation method, viz. by repeating the vinblastin precipitation step after resuspension of the sediment in a detergent-containing stabilizing medium. By this we overcome the deleterious influence of the yolk granules in the isolation procedure. From 1 l of Xenopus laevis eggs 25 mg VB-paracrystals can be obtained. The apparent molecular weight of the purified tubulin is 52,800. Antiserum against the purified Xenopus VB-paracrystals, raised in 2 Chinchilla rabbits, cross-reacts in immunodiffusion tests in agar gels with rat brain tubulin and with tubulin isolated from Xenopus laevis eggs by the described procedure. Specific indirect fluorescence staining and appropriate control reactions reveal that cilia of Tetrahymena pyriformis, cytoplasmic networks in cultured mouse Leydig cells, as well as mitotic spindles and nuclear regions in paraffin sections of Xenopus laevis blastulae, react with the antibodies against Xenopus laevis egg tubulin as well as with monoclonal antibodies against pig brain tubulin. These results provide additional evidence for the view that tubulin antibodies are neither species nor tissue specific and show that under appropriate conditions tubulin containing structures can be visualized in paraffin sections.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00489907
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  • 5
    Electronic Resource
    Electronic Resource
    Book reviews (1986)
    Springer
    Space science reviews 44 (1986), S. 393-409 
    Details
    ISSN: 1572-9672
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00200821
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