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  • 1
    Electronic Resource
    Electronic Resource
    Entwicklung der Gametogonien in ektopisch transplantierten Gonaden beiTriturus (1969)
    Springer
    Development genes and evolution 163 (1969), S. 287-297 
    Details
    ISSN: 1432-041X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung Nach homoplastischer Transplantation von larvalen Gonaden mit Pettkörper in die vordere Leibeshöhle wächst nur der Fettkörper an der Leber an, so daß die Gonade nur indirekt mit dem Wirtsgewebe verbunden ist. Die Differenzierung der Gametogonien folgt der Normogenese, bei Ovartransplantationen entwickeln sich Auxocyten. Nach spätestens 27 Tagen ist die Blutversorgung wiederhergestellt. Homo- und autoplastische Transplantationen von Gonaden ohne Fettkörper ergeben für die Gametogonien eine völlig andere Entwicklung. Sind die Gonaden mit breiter Fläche angewachsen, läßt sich bereits 7 Tage p.o. im Bereich der Kontaktzone Gonade-Leber die Karyolyse der Gametogonienkerne feststellen. Nach 3–4 Wochen stellt das Transplantat eine bindegewebige Zyste ohne Geschlechtszellen dar. Erythrozyten zeigen die Vaskularisation an. Ist nur ein Teil der Gonade mit der Leber verwachsen, zeigt der frei gebliebene Abschnitt eine normale Struktur mit Mitosen der Gametogonien. Die Degeneration der Geschlechtszellen hängt offenbar von ihrer Lage zum extragonadalen Gewebe ab.
    Notes: Summary Homografts of gonads including fat-bodies show fusion of the fat-body with liver tissue. Thus, contact between gonad and liver is only indirect. The differentiation of the gametogonia follows the normal way of development. In case of ovary homografts auxocytes appear. Not later than 27 days after transplantation vascularization is reestablished. Homo- and autografts of gonads without fat-body show a quite different development of the gametogonia. When the gonads are broadly fused with liver tissue one notices karyolysis of the gametogonia nuclei within the gonad liver contact region already 7 days after transplantation. After 3–4 weeks the graft represents a cyst formed by connective tissue without any germ cells. Erythrocytes indicate vascularization. In the gonad partly fused with liver normal structure and mitosis in the gametogonia appear in that part of the transplant not attached to liver tissue. The present experiments suggest that the degeneration of germ cells is depending on their position to extragonadal tissue.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00577016
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  • 2
    Electronic Resource
    Electronic Resource
    Identification of a soluble precursor complex essential for nuclear pore assembly in vitro (1990)
    Springer
    Chromosoma 100 (1990), S. 56-66 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract We analysed the soluble form in which the nuclear pore complex protein p68 is stored in Xenopus laevis eggs and its involvement in pore complex assembly processes. We have shown previously that p68, which is the major wheat germ agglutinin (WGA)-binding glycoprotein of nuclear pore complexes from Xenopus oocytes, is located in the pore channel and participates in mediated transport of karyophilic proteins. Using a monoclonal antibody directed against p68 (PI1) we removed this protein from Xenopus egg extract by immunoadsorption. On addition of lambda DNA the immunodepleted extract supported reconstitution of nuclei which were surrounded by a continuous double-membrane envelope but lacked pore complexes and were unable to import karyophilic proteins such as nucleoplasmin or lamin LIII. Essentially identical results were obtained with extract depleted of WGA-binding proteins. Our finding that both the anti-p68 antibody and WGA efficiently removed components from the extract necessary for pore complex assembly but did not interfere with nuclear membrane formation demonstrates that these processes are independent of each other. Analysis of the immunoprecipitate on silver-stained SDS-polyacrylamide gels indicated that the antibody adsorbed other proteins besides p68, notably two high molecular weight components. By sucrose gradient centrifugation and gel filtration we showed that p68 together with associated protein(s) forms a stable, approximately globular complex plex with an Mr of 254,000, a Stokes radius of 5.2 nm and a sedimentation coefficient of 11.3 S. Our finding that p68 occurs in the form of larger macromolecular assemblies offers an explanation for the distinctly punctate immunofluorescence pattern observed in the cytoplasm of mitotic cells after staining with antibodies to p68.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00337603
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  • 3
    Electronic Resource
    Electronic Resource
    Assigning functions to nucleolar structures (1991)
    Springer
    Chromosoma 101 (1991), S. 133-140 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00355363
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  • 4
    Electronic Resource
    Electronic Resource
    Lampbrush-type chromosomes in the primary nucleus of the green alga Acetabularia mediterranea (1975)
    Springer
    Chromosoma 50 (1975), S. 25-43 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Structures with a lampbrush-chromosome-like morphology are described in the nucleoplasm of primary nuclei of the green alga, Acetabularia mediterranea, by light and electron microscopy in sections of cells fixed in situ and in spread preparations of isolated nuclear components. These chromosomes reveal typical loops (up to 20 μm long), chromomere-like nodules (1–2 μm in diameter), and 2–4 μm large axial globules. Associations of some of these chromosomes with nucleolar structures and with the nuclear envelope are also recognized. The light microscopically identified loops are correlated with distinct fibrillogranular structures observed in the thin sections and with the very long matrix units seen in the spreadpreparations. The similarity of these structures to the lampbrush chromosomes of various animal cell types, all exclusively stages of meiotic prophase, is discussed as well as the possible relation of the appearance of lampbrush chromosomes to a defined phase of the vegetative growth of this alga.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00284960
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  • 5
    Electronic Resource
    Electronic Resource
    A bisexually reproducing all-triploid vertebrate (2002)
    [s.l.] : Nature Publishing Group
    Nature genetics 30 (2002), S. 325-328 
    Details
    ISSN: 1546-1718
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Medicine
    Notes: [Auszug] Green toads are common in the Palaearctic region, where they have differentiated into several taxa. The toads exist with variable amounts of ploidy, similar to other anuran species or reptiles. In vertebrate biology, the very rare occurrence of triploidy is coupled with infertility or unisexuality, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/ng839
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  • 6
    Electronic Resource
    Electronic Resource
    A monoclonal antibody against DNA topoisomerase II labels the axial granules of Pleurodeles lampbrush chromosomes (1996)
    Springer
    Chromosoma 104 (1996), S. 358-366 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract. By immunizing Balb/c mice with oocyte nuclei of Pleurodeles waltl we obtained a monoclonal antibody, mAb 4A6, that labels distinct globular domains of the lampbrush chromosomal axes of Pleurodeles. These domains are found at corresponding sites of homologous chromosomes, often at telomeric and putative centromeric regions, and appear to be devoid of DNA. Because of these characteristic features it is most likely that the mAb 4A6-positive domains correspond to the central part of the ”axial granules” of urodelan lampbrush chromosomes. In immunoblotting analyses mAb 4A6 reacts with a nuclear antigen of ∼M r 180000 and a structurally nonrelated cytoplasmic protein of M r 98000, which was not characterized any further. Comparative immunofluorescence and immunoblotting studies with mAb 4A6 and an antiserum against DNA topoisomerase II (topo II) as well as immunodepletion experiments demonstrated that the nuclear 4A6 antigen is topo II. Our results indicate that topo II is not a constituent of a continuous, loop-anchoring scaffold in lampbrush chromosomes of Pleurodeles but, rather, is restricted to the axial granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00337225
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  • 7
    Electronic Resource
    Electronic Resource
    Lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of Xenopus laevis (1977)
    Springer
    Chromosoma 60 (1977), S. 147-167 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Transcriptionally active chromatin from peripheral amplified nucleoli of lampbrush-chromosome stage oocytes of Xenopus laevis was dispersed and spread in various solutions of low salt concentrations (including some with additions of detergents) and examined by electron microscopy. Nucleolar material from oocytes of animals with normal (2-nu) and mutant (1-nu) genetical constitution of nucleolus organizers was compared. Histograms showing the distributions of the lengths of matrix units, apparent spacer intercepts, and the total repeating units of the rDNA containing chromatin axes revealed a significant degree of heterogeneity, with indications of subclasses and predominant repeat unit size classes of 3.3 and 3.8 μm length. The correspondence of matrix unit length to the molecular weight of the first stable product of rDNA transcription was studied using gel electrophoresis of labelled pre-rRNA under non-denaturing and denaturing conditions. Evaluations of individual strands of nucleolar chromatin further demonstrated the existence of both (i) strands with obviously homogeneous repeating units and (ii) strands with intra-axial heterogeneity of rDNA subunits. “Preludecomplexes”, i.e. groups of transcriptional complexes in apparent spacer intercepts, were not infrequently noted. The data are compared with the measurements of lengths of repeating units in fragments of rDNA obtained by digestion with EcoRI endonuclease as described by Morrow et al. (1974) and Wellauer et al. (1974, 1976a, b). The results are discussed in relation to problems of variations in the modes of arrangement of the pre-rRNA genes, the state of packing of rDNA during transcription, and possible mechanisms of the amplification process.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00288462
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  • 8
    Electronic Resource
    Electronic Resource
    Nucleosomal and supranucleosomal organization of transcriptionally inactive rDNA circles in Dytiscus oocytes (1978)
    Springer
    Chromosoma 69 (1978), S. 243-254 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Oocytes of the water beetle, Dytiscus marginalis, contain large amounts of rDNA most of which is present in the form of rings containing one or several pre-rRNA genes. Electron microscopy of spread preparations of vitellogenic oocytes has shown that the rDNA is extended in chromatin rings with transcribed pre-rRNA genes and is not packed into nucleosomes (Trendelenburg etal., 1976). When similar preparations are made from previtellogenic ooytes in which a large proportion of the nucleolar chromatin is transcriptionally inactive, a different morphological form of this chromatin is recognized. In contrast to the transcribed chromatin rings the inactive nucleolar chromatin circles show the characteristic beaded configuration, indicative of nucleosomal packing. Nucleosomal packing is also indicated by the comparison of the lengths of these chromatin rings with both isolated rDNA circles and transcribed chromatin rings. In addition, these inactive nucleofilaments often appear to be compacted into globular higher order structures of diameters from 21 to 34nm, each composed of an aggregate of 6–9 nucleosomes. While the estimated reduction of the overall length of rDNA, as seen in our preparations, is, on the average, only 2.2–2.4 fold in the nucleosomal state it is 10–13 fold when supranucleosomal globules are present. These data show that the extrachromosomal rDNA of these oocytes goes through a cycle of condensation and extension, as a function of the specific transcriptional activity, and that the beaded state described here is exclusively found in the non-transcribed state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00329922
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  • 9
    Electronic Resource
    Electronic Resource
    Transcription of complementary repeat sequences in amphibian oocytes (1982)
    Springer
    Chromosoma 86 (1982), S. 95-113 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract Repeat sequences are transcribed in the germinal vesicles of amphibian oocytes. In the hnRNA population both complements of the repeats are found and can be readily detected because they form intermolecular duplex structures. The structure and formation of duplex regions have been studied in the hnRNA of Xenopus laevis, Triturus cristatus, Amphiuma means and Necturus maculosus, a series of amphibians of increasing genome size (C-value). In T. cristatus, the duplex structures are mostly 600–1200 bp in length, whereas in X. laevis they are shorter and in N. maculosus they tend to be longer. Although the proportion of RNA sequence capable of rapidly forming duplex structures is different in different organisms, this property bears no relationship to C-value. However the sequence complexity of complementary repeats, as estimated from the rate of duplex formation, does show an increasing trend with C-value. The complementary repeats found in oocyte hnRNA are transcribed from families of DNA sequence that are each represented in the genome by thousands of copies. The extent of cross-species hybridization is low, indicating that the repeat sequences transcribed in different amphibian genera are not the same. In situ hybridization experiments indicate that the repeat sequences are spread throughout the genome. The evolution and possible function of complementary repeats are considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00330732
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  • 10
    Electronic Resource
    Electronic Resource
    A monoclonal antibody against DNA topoisomerase II labels the axial granules of Pleurodeles lampbrush chromosomes (1996)
    Springer
    Chromosoma 104 (1996), S. 358-366 
    Details
    ISSN: 1432-0886
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Medicine
    Notes: Abstract By immunizing Balb/c mice with oocyte nuclei of Pleurodeles waltl we obtained a monoclonal antibody, mAb 4A6, that labels distinct globular domains of the lampbrush chromosomal axes of Pleurodeles. These domains are found at corresponding sites of homologous chromosomes, often at telomeric and putative centromeric regions, and appear to be devoid of DNA. Because of these characteristic features it is most likely that the mAb 4A6-positive domains correspond to the central part of the “axial granules” of urodelan lampbrush chromosomes. In immunoblotting analyses mAb 4A6 reacts with a nuclear antigen of ∼M r 180000 and a structurally nonrelated cytoplasmic protein of M r 98000, which was not characterized any further. Comparative immunofluorescence and immunoblotting studies with mAb 4A6 and an antiserum against DNA topoisomerase II (topo II) as well as immunodepletion experiments demonstrated that the nuclear 4A6 antigen is topo II. Our results indicate that topo II is not a constitutent of a continuous, loop-anchoring scaffold in lampbrush chromosomes of Pleurodeles but, rather, is restricted to the axial granules.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00337225
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