@article{FrankeScheerTrendelenburgetal.1976,
  author    = {Franke, Werner W. and Scheer, Ulrich and Trendelenburg, Michael F. and Spring, Herbert and Zentgraf, Hanswalter},
  title     = {Absence of nucleosomes in transcriptionally active chromatin},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40646},
  year      = {1976},
  abstract  = {The ultrastructure of twO kinds of transcription ally active chromatin, the lampbrush chromosome loops and the nucleoli from amphibian oocytes and primary nuclei of the green alga Acetabularia, has been examined after manual isolation and dispersion in low salt media of slightly alkaline pH using various electron microscopic staining techniques (positive staining, metal shadowing, negative staining, preparation on positively charged films, etc.) and compared with the appearance of chromatin from various somatic cells (hen erythrocytes, rat hepatocytes, ClIltured murine sarcoma cells) prepared in parallel. While typical nucleosomes were revealed with all the techniques for chromatin from the latter three cell system, no nucleosomes were identified in either the lampbrush chromosome structures or the nucleolar chromatin. Nucleosomal arrays were absent not only in maximally fibril-covered matrix units but also in fibril-free regions between transcriptional complexes, including the apparent spacer intercepts between different transcriptional units. Moreover, comparisons of the length of the repeating units of rDNA in the transcribed state with those determined in the isolated rDNA and with the lengths of the first stable product of rDNA transcription, the pre-rRNA, demonstrated that the transcribed rDNA was not significantly shortened and/or condensed but rather extended in the transcriptional units. Distinct granules of about nucleosomal size which were sometimes found in apparent spacer regions as well as within matrix units of reduced fibril density were shown not to represent nucleosomes since their number per spacer unit was not inversely correlated with the length of the specific unit and also on the basis of their resistance to treatment with the detergent Sarkosyl NL-30. It is possible to structurally distinguish between transcriptionally active chromatin in which the DNA is extended in a non-nucleosomal form of chromatin and condensed, inactive chromatin within the typical nucleosomal package. The characteristic extended structure of transcriptionally active chromatin is found not only in the transcribed genes but also in non-transcribed regions within or between ("spacer") transcriptional units as well as in transcriptional units that are untranscribed amidst transcribed ones and/or have been inactivated for relatively short time. It is hypothesized that activation of transcription involves a transition from a nucleosomal to an extended chromatin organisation and that this structural transition is not specific for single "activated" genes but may involve larger chromatin regions, including adjacent untranscribed intercepts.},
  subject      = {Cytologie},
  language  = {en}
}
@inproceedings{ScheerFranke1976,
  author    = {Scheer, Ulrich and Franke, Werner W.},
  title     = {Transcriptional complexes of nucleolar genes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41072},
  year      = {1976},
  abstract  = {No abstract available},
  language  = {en}
}
@article{ScheerMessnerHazanetal.1987,
  author    = {Scheer, Ulrich and Messner, Karin and Hazan, Rachel and Raska, Ivan and Hansmann, Paul and Falk, Heinz and Spiess, Eberhard and Franke, Werner W.},
  title     = {High sensitivity immunolocalization of double and single-stranded DNA by a monoclonal antibody},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41063},
  year      = {1987},
  abstract  = {A monoclonal antibody (AK 30-10) is described which specifically reacts with DNA both in double and single-stranded forms but not with other molecules and structures, including deoxyribonucleotides and RNAs. When used in immunocytochemical experiments on tissue sections and permeabilized cultured cells, this antibody detects DNA-containing structures, even when the DNA is present in very small amounts. Examples of high resolution detection include the DNA present in amplified extrachromosomal nucleoli, chromomeres of lampbrush chromosomes, mitochondria, chloroplasts and mycoplasmal particles. In immunoelectron microscopy using the immunogold technique, the DNA was localized in distinct substructures such as the "fibrillar centers" of nucleoli and certain stromal centers in chloroplasts. The antibody also reacts with DNA of chromatin of living cells, as shown by microinjection into cultured mitotic cells and into nuclei of amphibian oocytes. The potential value and the limitations of immunocytochemical DNA detection are discussed.},
  subject      = {Cytologie},
  language  = {en}
}
@article{Scheer1980,
  author    = {Scheer, Ulrich},
  title     = {Structural organization of spacer chromatin between transcribed ribosomal RNA genes in amphibian oocytes},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41057},
  year      = {1980},
  abstract  = {Transcribed nucleolar chomatin, including the spacer regions interspersed between the rRNA genes, is different from the bulk of nontranscribed chromatin in that the DNA of these regions appears to be in an extended (B) conformation when examined by electron microscopy. The possibility that this may reflect artificial unfolding of nucleosomes during incubation in very low salt buffers as routinely used in such spread preparations has been examined by studying the influence of various ion concentrations on nucleolar chromatin structure. Amplified nucleolar chromatin of amphibian oocytes (Xenopus laevis, Pleurodeles waltlii, Triturus cristatus) was spread in various concentrations of NaCl (range 0 to 20 mM). Below 1 mM salt spacer chromatin frequently revealed a variable number of irregularly shaped beads, whereas above this concentration the chromatin axis appeared uniformly smooth. At all salt concentrations studied, however, the length distribution of spacer and gene regions was identical. Preparations fixed with glutaraldehyde instead of formaldehyde, or unftxed preparations, were indistinguishable in this respect. The observations indicate that (i) rDNA spacer regions are not compacted into nucleosomal particles and into supranucleosomal structures when visualized at chromatin stabilizing salt concentrations (e.g., 20 mM NaCl), and (ii) spacer DNA is covered by a uniform layer of proteins of unknown nature which, at very low salt concentrations (below 1 mM NaCl), can artificially give rise to the appearance of small granular particles of approximately nucleosome-like sizes. These particles, however, are different from nucleosomes in that they do not foreshorten the associated spacer DNA. The data support the concept of an altered nucleohistone conformation not only in transcribed chromatin but also in the vicinity of transcriptional events.},
  subject      = {Cytologie},
  language  = {en}
}
@article{Scheer1969,
  author    = {Scheer, Ulrich},
  title     = {Entwicklung der Gametogonien in ektopisch transplantierten Gonaden bei Triturus},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40510},
  year      = {1969},
  abstract  = {Nach homoplastischer Transplantation von larvalen Gonaden mit Fettkiirper in die vordere Leibeshiihle wiichst nur der Fettkiirper an der Leber an, so daB die Gonade nur indirekt mit dem Wirtsgewebe verbunden ist. Die Differenzierung der Gametogonien folgt der Normogenese, bei Ovartransplantationen entwickeln sich Auxocyten. Nach spatestens 27 Tagen ist die Blutversorgung wiederhergestellt. Homo- und autoplastische Transplantationen von Gonaden oh ne Fettkiirper ergeben fUr die Gametogonien eine vollig andere Entwicklung. Sind die Gonaden mit breiter Fliiche angewachsen, liiBt si ch 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. 1st 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 hiingt offenbar von ihrer Lage zum extragonadalen Gewebe ab.},
  language  = {de}
}
@incollection{ScheerDabauvalle1985,
  author    = {Scheer, Ulrich and Dabauvalle, Marie-Christine},
  title     = {Functional organization of the amphibian oocyte nucleus},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41178},
  publisher      = {Universit{\"a}t W{\"u}rzburg},
  year      = {1985},
  abstract  = {No abstract available},
  subject      = {Oogenese},
  language  = {en}
}
@article{Scheer1986,
  author    = {Scheer, Ulrich},
  title     = {Injection of antibodies into the nucleus of amphibian oocytes: an experimental means of interfering with gene expression in the living cell},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41182},
  year      = {1986},
  abstract  = {No abstract available},
  language  = {en}
}
@misc{DabauvalleScheer1991,
  author    = {Dabauvalle, Marie-Christine and Scheer, Ulrich},
  title     = {Assembly of nuclear pore complexes in Xenopus egg extract},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41194},
  year      = {1991},
  abstract  = {No abstract available},
  language  = {en}
}
@article{HockMoormannFischeretal.1993,
  author    = {Hock, Robert and Moormann, Antoon and Fischer, Dagmar and Scheer, Ulrich},
  title     = {Absence of somatic histone H1 in oocytes and preblastula embryos of Xenopus laevis},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41350},
  year      = {1993},
  abstract  = {Available data on the occurrence and expression of somatic histone HI during oogenesis and early embryogenesis of Xenopus laevis are contradictory. In particular the reported presence of a large storage pool of histone HIA in oocytes is difficult to reconcile with the high transcriptional activity of all gene classes in this specific cell type. In the present study we have used polyclonal antibodies raised against somatic Xenopus histone HI (HIA and HIA/B) for combined immunoblotting experiments to quantitate HI pools and immunolocalization studies to visualize chromosome- bound HI. Both approaches failed to detect soluble or chromosomal histone HI in vitellogenic oocytes, eggs, and cleavage-stage embryos up to early blastula. In addition, chromatin assembled in Xenopus egg extract was also negative for histone HI as revealed by immunofluorescence microscopy. Lampbrush chromosomes not only lacked histone HI but also the previously identified histone HI-like B4 protein (Smith et al., 1988, Genes Dev. 2,1284-1295). In contrast, chromosomes of eggs and early embryos fluoresced brightly with anti-B4 antibodies. Our results lend further support to the view that histone HI expression is developmentally regulated during Xenopus oogenesis and embryogenesis similar to what is known from other species.},
  language  = {en}
}
@article{KleinschmidtScheerDabauvalleetal.1983,
  author    = {Kleinschmidt, J{\"u}rgen A. and Scheer, Ulrich and Dabauvalle, Marie-Christine and Bustin, Michael and Franke, Werner W.},
  title     = {High mobility group proteins of amphibian oocytes: a large storage pool of a soluble high mobility group-1-like protein and involvement in transcriptional events},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-33250},
  year      = {1983},
  abstract  = {No abstract available},
  language  = {en}
}