@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} } @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} } @inproceedings{FrankeScheerTrendelenburgetal.1978, author = {Franke, Werner W. and Scheer, Ulrich and Trendelenburg, Michael F. and Zentgraf, H. and Spring, H.}, title = {Morphology of transcriptionally active chromatin}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41097}, year = {1978}, abstract = {Some decades ago it was noted by cytologists that within the interphase nucleus large portions of the transcriptionally ("genetically," in their terms) inactive chromosomal material are contained in aggregates of condensed chromatin, the "chromocenters," whereas transcriptionally active regions of chromosomes appear in a more dispersed form and are less intensely stained with DNA-directed staining procedures (Heitz 1929, 1932, 1956; Bauer 1933). The hypothesis that condensed chromatin is usually characterized by very low or no transcriptional activity, and that transcription occurs in loosely packed forms of chromatin (including, in most cells, the nucleolar chromatin) has received support from studies of ultrathin sections in the electron microscope and from the numerous attempts to separate transcriptionally active from inactive chromatin biochemically (for references, see Anderson et al. 1975; Berkowitz and Doty 1975; Krieg and Wells 1976; Rickwood and Birnie 1976; Gottesfeld 1977). Electron microscopic autoradiography has revealed that sites of RNA synthesis are enriched in dispersed chromatin regions located at the margins of condensed chromatin (Fakan and Bernhard 1971, 1973; Bouteille et al. 1974; Bachellerie et al. 1975) and are characterized by the occurrence of distinct granular and fibrillar ribonucleoprotein (RNP) structures, such as perichromatin granules and fibrils. The discovery that, in most eukaryotic nuclei, major parts of the chromatin are organized in the form of nucleosomes (Olins and Olins 1974; Kornberg 1974; Baldwin et al. 1975) has raised the question whether the same nucleosomal packing of DNA is also present in transcriptionally active chromatin strands. Recent detailed examination of the morphology of active and inactive chromatin involving a diversity of electron microscopic methods, particularly the spreading technique by Miller and coworkers (Miller and Beatty 1969; Miller and Bakken 1972), has indicated that the DNA of some actively transcribed regions is not packed into nucleosomal particles but is present in a rather extended form within a relatively thin (4-7 nm) chromatin fiber.}, language = {en} } @incollection{ScheerZentgraf1982, author = {Scheer, Ulrich and Zentgraf, Hanswalter}, title = {Morphology of nucleolar chromatin in electron microscopic spread preparations}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41155}, publisher = {Universit{\"a}t W{\"u}rzburg}, year = {1982}, abstract = {No abstract available}, language = {en} } @article{HuegleScheerFranke1985, author = {H{\"u}gle, Barbara and Scheer, Ulrich and Franke, Werner W.}, title = {Ribocharin: a nuclear M\(_r\) 40,000 protein specific to precursor particles of the large ribosomal subunit}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-41169}, year = {1985}, abstract = {Using a monoclonal antibody (No-194) we have identified, in Xenopus laevis and other amphibia, an acidic protein of M, 40,000 (ribocharin) which is specifically associated with the granular component of the nucleolus and nucleoplasmic 65S particles. These particles contain the nuclear 28S rRNA and apparently represent the precursor to the large ribosomal subunit in nucleocytoplasmic transit. By immunoelectron microscopy ribocharin has been localized in the granular component of the nucleolus and in interchromatin granules. During mitosis ribocharin-containing particles are associated with surfaces of chromosomes and are recollected in the reconstituting nucleoli in late telophase. We suggest that ribocharin is a specific component of precursor particles of the large ribosomal subunit, which dissociates from the 65S particle before passage through the nuclear envelope, and is reutilized in ribosome biogenesis.}, language = {en} } @article{WeberSchmidtScheer1989, author = {Weber, Thomas and Schmidt, Erwin and Scheer, Ulrich}, title = {Mapping of transcription units on Xenopus laevis lampbrush chromosomes by in situ hybridization with biotin-labeled cDNA probes}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40763}, year = {1989}, abstract = {A non-radioactive in situ hybridization method is described for the localization of transcription units of defined genes to lateral loops of Xenopus laevis lampbrush chromosomes. Two Xenopus cONA probes were used encoding the nucleolar protein N038/ B23 and cytokeratin 1(8). Both proteins are known to be synthesized in Xenopus oocytes, and Northern blot analysis revealed the presence of the corresponding mRNAs in different oogenic stages. The probes were enzymatically labeled with biotin-dCTP and hybridized to lampbrush chromosomes. The sites of hybridization were detected either by indirect immunofluorescence microscopy using rabbit antibodies against biotin and fluorescein-conjugated antirabbit IgG or enzymatically using peroxidase-conjugated streptavi din. The probe encoding the nucleolar protein hybridized to two sets of lateral loops on different bivalents, the cytokeratin probe to at least four. Our finding that each probe hybridized to more than one chromosomal locus may reflect the tetraploid nature of the Xenopus laevis genome or results from cross-hybridization to other transcriptionally active members of the N038/ B23-nucleoplasmin or the cytokeratin-Iamin gene families. The method described should facilitate further in situ hybridization studies with appropriate genomic clones in order to map specific DNA sequences to defined loop regions and to come to a better understanding of the relationship between loop organization and gene transcription unit.}, subject = {Cytologie}, language = {en} } @article{BenaventeDabauvalleScheeretal.1989, author = {Benavente, Ricardo and Dabauvalle, Marie-Christine and Scheer, Ulrich and Chaly, Nathalie}, title = {Functional role of newly formed pore complexes in postmitotic nuclear reorganization}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40754}, year = {1989}, abstract = {Many nuclear proteins are released into the cytoplasm at prometaphase and are transported back into the daughter nuclei at the end of mitosis. To determine the role of this reentry in nuclear remodelling during early interphase, we experimentally manipulated nuclear protein uptake in dividing cells. Recently we and others have shown that signal-dependent, pore complex-mediated uptake of nuclear protein is blocked in living cells on microinjection of the lectin wheat germ agglutinin (WGA), or of antibodies such as PI1 that are directed against WGA-binding pore complex glycoproteins. In the present study, we microinjected mitotic PtKz cells with WGA or antibody PIt and followed nuclear reorganization of the daughter cells by immunofluorescence and electron microscopy. The inhibitory effect on nuclear protein uptake was monitored by co-injection of the karyophilic protein nucleoplasmin. When injected by itself early in mitosis, nucleoplasmin became sequestered into the daughter nuclei as they entered telophase. In contrast, nucleoplasmin was excluded from the daughter nuclei in the presence of WGA or antibody PI1 . Although PtKz cells with blocked nuclear protein uptake completed cytokinesis, their nuclei showed a telophaselike organization characterized by highly condensed chromatin surrounded by a nuclear envelope containing a few pore complexes. These findings suggest that pore complexes become functional as early as telophase, in close coincidence with nuclear envelope reformation. They further indicate that the extensive structural rearrangement of the nucleus during the telophase-G1 transition is dependent on the influx of karyophilic proteins from the cytoplasm through the pore complexes, and is not due solely to chromosome- associated components.}, language = {en} } @article{ThiryScheerGoessens1988, author = {Thiry, Marc and Scheer, Ulrich and Goessens, Guy}, title = {Immunoelectron microscopic study of nucleolar DNA during mitosis in Ehrlich tumour cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40745}, year = {1988}, abstract = {In order to investigate the DNA localization within Ehrlich tumor cell nucleoli during mitosis, two recent immunocytochemical methods using either an anti-DNA or an anti-bromodeoxyuridine (BrdU) monoclonal antibody have been applied. In both cases, the immunogold labeling has been performed on ultrathin sections of cells embedded either in Lowicryl K4M or in Epon, respectively. Identical results are observed with both immunocytochemical approaches. In the interphase nucleolus, besides the labeling of the perinucleolar chromatin shell and of its intranucleolar invaginations which penetrate into the nucleolar body and often terminate at the fibrillar centers, a few gold particles are also preferentially found towards the peripheral region of the fibrillar centers. In contrast, the dense fibrillar component and the granular component are never labeled. During mitosis, the fibrillar centers persist at the chromosomal nucleolus organizing regions (NOR's) and can be selectively stained by the silver method. However, these metaphase fibrillar centers are no longer decorated by the DNA- or BrdU antibodies. These results indicate that until the end of prophase, rRNA genes are present inside the fibrillar center material, disappear during metaphase and reappear in reconstituting nucleoli during telophase. Thus, fibrillar centers appear to represent structures sui generis, which are populated by rRNA genes only when the nucleolus is functionally active. In segregated nucleoli after actinomycin D treatment, the DNA labeling is exclusively restricted to the perinucleolar chromatin blocks. These findings also suggest that the DNA content of the fibrillar center material varies according to the rRNA transcription level of the cells. The results are discussed in the light of the present knowledge of the functional organization of the nucleolus.}, subject = {Cytologie}, language = {en} } @article{BenaventeReimerRoseetal.1988, author = {Benavente, Ricardo and Reimer, Georg and Rose, Kathleen M. and H{\"u}gle-D{\"o}rr, Barbara and Scheer, Ulrich}, title = {Nucleolar changes after microinjection of antibodies to RNA polymerase I into the nucleus of mammalian cells}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40666}, year = {1988}, abstract = {After microinjection of antibodies against RNA polymerase I into the nuclei of cultured rat kangaroo (PtKz) and rat (RVF-SMC) cells alterations in nucleolar structure and composition were observed. These were detected by electron microscopy and double-label immunofluorescence microscopy using antibodies to proteins representative of the three major components of the nucleolus. The microinjected antibodies produced a progressive loss of the material of the dense fibrillar component (DFC) from the nucleoli which, at 4 h after injection, were transformed into bodies with purely granular component (GC) structure with attached fibrillar centers (FCs). Concomitantly, numerous extranucleolar aggregates appeared in the nucleoplasm which morphologically resembled fragments of the DFC and contained a protein (fibrillarin) diagnostic for this nucleolar structure. These observations indicate that the topological distribution of the material constituting the DFC can be experimentally influenced in interphase cells, apparently by modulating the transcriptional activity of the rRNA genes. These effects are different from nucleolar lesions induced by inhibitory drugs such as actinomycin D-dependent "nucleolar segregation". The structural alterations induced by antibodies to RNA polymerase I resemble, however, the initial events of nucleolar disintegration during mitotic prophase.}, language = {en} } @incollection{FrankeScheerZentgrafetal.1980, author = {Franke, Werner W. and Scheer, Ulrich and Zentgraf, Hanswalter and Trendelenburg, Michael F. and M{\"u}ller, U. and Krohne, G. and Spring, H.}, title = {Organization of transcribed and nontranscribed chromatin}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-40656}, publisher = {Universit{\"a}t W{\"u}rzburg}, year = {1980}, abstract = {No abstract available}, subject = {Tumor / Zellteilung}, language = {en} }