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  • 1
    Electronic Resource
    Electronic Resource
    Primary structure and evolutionary relationship between the adult α-globin genes and their 5′-flanking regions ofXenopus laevis andXenopus tropicalis (1988)
    Springer
    Journal of molecular evolution 28 (1988), S. 64-71 
    Details
    ISSN: 1432-1432
    Keywords: Xenopus laevis ; Xenopus tropicalis ; Adult α-globin genes ; Gene organization ; Conserved upstream sequences
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To investigate the evolution of globin genes in the genusXenopus, we have determined the primary structure of the related adult α1- and αII genes ofX. laevis and of the adult α-globin gene ofX. tropicalis, including their 5′-flanking regions. All three genes are comprised of three exons and two introns at homologous positions. The exons are highly conserved and code for 141 amino acids. By contrast, the corresponding introns vary in length and show considerable divergence. Comparison of 900 bp of the 5′-flanking region revealed that theX. tropicalis gene contains a conserved proximal 310-bp promoter sequence, comprised of the canonical TATA and CCAAT motifs at homologous positions, and five conserved elements in the same order and at similar positions as previously shown for the corresponding genes ofX. laevis. We therefore conclude that these conserved upstream elements may represent regulatory sequences for cell-specific regulation of the adultXenopus globin genes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02143498
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  • 2
    Electronic Resource
    Electronic Resource
    Über das System TiO−LiTiO2 (1966)
    Springer
    Naturwissenschaften 53 (1966), S. 251-251 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00637117
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  • 3
    Electronic Resource
    Electronic Resource
    Transcription of single-copy vitellogenin gene of Xenopus involves expression of middle repetitive DNA (1981)
    [s.l.] : Nature Publishing Group
    Nature 291 (1981), S. 429-431 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] To identify and locate the repetitive DNA found in the Al vitellogenin gene we constructed subclones of the seven largest introns of the Al vitellogenin gene (Fig. 1). This was achieved by insertion of 400-600-base pair fragments derived from the cloned A gene into the plasmid pBR322. ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/291429a0
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  • 4
    Electronic Resource
    Electronic Resource
    Factors promoting the establishment of primary cultures of liver cells fromXenopus larvae (1977)
    Springer
    Development genes and evolution 182 (1977), S. 347-360 
    Details
    ISSN: 1432-041X
    Keywords: Xenopus larvae ; Liver ; Primary culture ; Plating efficiency ; Cell proliferation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The requirements for establishment and survival of primary cultures of larval amphibian liver cells were investigated. Plating efficiency was found to be enhanced by a collagen substrate, by diluted conditioned medium from an adultXenopus kidney cell line and by high initial cell densities. Plating efficiency was highest at a tonicity of 165–220 mOsm/kg. In cultures with undiluted conditioned medium the increase in cell number was 50–60% greater than in controls, where it was about 2-fold between day 3 and 6 of culture. Conditioned medium from theXenopus kidney cell line is assumed to contain at least two components, which are effective at different concentrations and stimulate either plating efficiency and cell aggregation or cell proliferation. In cultures without collagen sheets, cell flattening is greatly reduced, indicating that cell shape is also dependent upon the substrate.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00848385
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  • 5
    Electronic Resource
    Electronic Resource
    The metamorphic switch in hemoglobin phenotype ofXenopus laevis involves erythroid cell replacement (1989)
    Springer
    Development genes and evolution 198 (1989), S. 57-64 
    Details
    ISSN: 1432-041X
    Keywords: Hemoglobin transition ; Erythrocytes ; Indirect immunofluorescence ; Metamorphosis ; Xenopus laevis
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary To elucidate the cellular basis of hemoglobin transition inXenopus laevis the distribution of larval and adult hemoglobins was analyzed by indirect immunofluorescence in the circulating erythrocytes during metamorphosis. In addition, the morphological characteristics as well as the capacity for synthesis of DNA and hemoglobin in the erythrocytes were followed during the same developmental period. Our quantitative analysis on the distribution of larval and adult hemoglobins suggests that they are localized in different cells. Hemoglobin transition, therefore, most likely reflects replacement of the larval erythrocyte population by new cells which are committed to adult globin synthesis. Since hemoglobin transition is not accompanied by an increase in the abundance of immature erythroid cells with active DNA synthesis, we assume that the presumptive adult erythroid cells are released into circulation at a relatively advanced stage of maturation. The decline in the synthesis of DNA and larval hemoglobin further indicates that cessation of cell renewal in the larval erythrocyte population may represent a decisive step in hemoglobin transition.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF02447740
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  • 6
    Electronic Resource
    Electronic Resource
    Über die submikroskopische Organisation und die biochemische Kennzeichnung embryonaler Entwicklungsstadien vonTubifex (1958)
    Springer
    Development genes and evolution 150 (1958), S. 542-580 
    Details
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00575992
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  • 7
    Electronic Resource
    Electronic Resource
    Spontane und induzierte Metamorphose bei Larven des Krallenfrosches (Xenopus laevis Daud.) im Kälteversuch (1970)
    Springer
    Development genes and evolution 165 (1970), S. 342-355 
    Details
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Bei jungenXenopuslarven (Prämetamorphose) ist die Mortalität im Bereich von 8,5–22° C konstant, nimmt jedoch unterhalb von 8,5° C stark zu. Die Wirkung der Kälte (10° C) auf die spontane Metamorphose zeigt stadienspezifische Unterschiede. Eine vollkommene Metamorphosehemmung gelingt nur bei Prämetamorphoselarven; bei älteren Larven (Prometamorphose) ist die Umwandlung nur verzögert. Blockierte Larven können in der Kälte durch Behandlung mit Thyroxin bzw. TSH zur Metamorphose veranlaßt werden. Da weder die Ansprechbarkeit larvaler Gewebe auf Thyroxin, noch diejenige der Schilddrüse auf TSH betroffen sind, muß die kältebedingte Metamorphosehemmung auf einer Blockierung des übergeordneten Steuerungszentrums beruhen.
    Notes: Summary In premetamorphicXenopus larvae mortality is not influenced by lowering the temperature from 22° to 8.5° C, but it rises dramatically below 8.5° C. At 10° C complete inhibition of spontaneous metamorphosis occurs only in premetamorphic larvae; beyond stage 56 cold treatment only delays the metamorphic changes. In cold-arrested premetamorphic larvae thyroxine and TSH elicit metamorphic responses. Since the responding capacity of the larval tissues to thyroxine is not affected, blockage of spontaneous metamorphosis at low temperature must result from the inhibition of the hypothalamic center.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00573678
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  • 8
    Electronic Resource
    Electronic Resource
    Immunological analysis of hemoglobin transition during metamorphosis of normal and isogenicXenopus (1980)
    Springer
    Development genes and evolution 188 (1980), S. 75-80 
    Details
    ISSN: 1432-041X
    Keywords: Hemoglobin transition ; Immunoelectrophoresis ; Quantitative Immunodiffusion ; Metamorphosis ; Xenopus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Antisera against larval and adultXenopus hemoglobins as well as adult human hemoglobin showed no cross-reaction when tested by immunodiffusion against each heterologous antigen. In this test hemoglobin of a single animal produced two precipitation lines for larvae, but only one for adult stages. Immunoelectrophoresis also revealed more complex precipitation patterns for larval than for adult hemoglobins. Hemoglobin of the isogenic hybrid cloneXenopus laevis/X. gilli also reacted with antisera against normalXenopus hemoglobin. Quantitation of hemoglobins, analyzed by radial immunodiffusion showed fewer than 1% of adult hemoglobin in red cells of larvae, but 30% at completion of metamorphosis. Two weeks later adult hemoglobin attained over 90%, and in red cells of adultXenopus an average of 1% larval hemoglobin were detected. The relatively short transition period suggests that the loss of larval hemoglobin may be due to the elimination of larval red cells, and that the increase in adult hemoglobin may be indicative of a new cell line.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00848612
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  • 9
    Electronic Resource
    Electronic Resource
    Retention of the differentiated state by larvalXenopus liver cells in primary culture (1978)
    Springer
    Development genes and evolution 185 (1978), S. 235-248 
    Details
    ISSN: 1432-041X
    Keywords: Liver ; Primary culture ; Ultrastructure ; Albumin synthesis ; Xenopus
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Electron microscopic analysis of primary cultures derived from larvalXenopus liver has shown that these cells, although they form only two-dimensional aggregates, retain and presumably also develop structural characteristics typical of liver parenchyma cells, such as bile canaliculi with microvilli and epithelial junctional complexes. As judged from structural criteria, primary cultures contain 80–90% hepatocytes. In contrast to the intact tissue, primary cultures showed excessive development of microfilaments, however. Incorporation of labeled amino acids has revealed further that the capacity for protein synthesis is maintained in culture and that synthesis of liverspecific protein albumin is maintained in vitro, even in liver cultures derived from thyrostatic tadpoles. This latter result suggests that initiation of albumin synthesis in the larval liver is probably not dependent upon thyroid hormones but rather reflects the protodifferentiated state of this tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00848354
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  • 10
    Electronic Resource
    Electronic Resource
    Hemoglobin transition in relation to metamorphosis in normal and isogenicXenopus (1977)
    Springer
    Development genes and evolution 183 (1977), S. 307-323 
    Details
    ISSN: 1432-041X
    Keywords: Hemoglobin transition ; Xenopus ; Metamorphosis ; Disc electrophoresis ; Amino acid incorporation
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Electrophoretic separation of hemoglobins of normalXenopus laevis and of isogenic animals derived from female hybrids ofXenopus laevis×Xenopus gilli revealed 5–9 components in premetamorphic larvae, and 3–4 components in adult toads. InXenopus laevis the number of larval hemoglobin components showed considerable variation, but this variation was absent in isogenic tadpoles, suggesting a genetic basis for hemoglobin polymorphism in larvae. Electrophoretic separation of larval and adult hemoglobins at different concentrations of acrylamide and treatment of these solutions with mercaptoethanol revealed that larval hemoglobin components are charge isomers, whereas adult hemoglobin was found to contain a minor dimeric component. Estimation of hemoglobin components showed that the main increase in adult hemoglobin, i.e from 30–90% of total hemoglobin, occurs within 4 weeks after completion of metamorphosis. By incroporation of3H amino acids in vivo a switch to preferential synthesis of adult hemoglobin and a corresponding decrease in larval hemoglobin production could be demonstrated during early climax stages. This suggests that thyroid hormones are involved in the hemoglobin transition. Yet chemical inhibition of the larval thyroid by thiourea resulted in a delayed but complete hemoglobin transition without morphological transformation. It is concluded that hemoglobin transition and morphological transformation of theXenopus tadpole require different concentrations of thyroid hormones.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00848460
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