TY - JOUR A1 - Scheer, Ulrich A1 - Hinssen, Horst A1 - Franke, Werner W. A1 - Jockusch, Brigitte M. T1 - Microinjection of actin-binding proteins and actin antibodies demonstrates involvement of nuclear actin in transcription of lampbrush chromosomes N2 - Nuclei of amphibian oocytes contain large amounts of actin, mostly in unpolymerized or short-polymer form. When antibodies to actin or actin-binding proteins (fragmin and the actin modulator from mammalian smooth muscle) are injected into nuclei of living oocytes of Pleurodeles waltlii, transcription of the lampbrush chromosomes, but not of the rRNA genes, is inhibited. When transcription is repressed by drugs or RNA is digested by microinjection of RNAase into oocyte nuclei, an extensive meshwork of actin filament bundles is seen in association with the isolated lampbrush chromosomes. These observations indicate a close relationship between the state of nuclear actin and transcriptional activity and suggest that nuclear actin may be involved in transcriptional events concerning protein-coding genes. Y1 - 1984 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39706 ER - TY - JOUR A1 - Hügle, Barbara A1 - Hazan, Rachel A1 - Scheer, Ulrich A1 - Franke, Werner W. T1 - Localization of ribosomal protein S1 in the granular component of the interphase nucleolus and its distribution during mitosis N2 - Using antibodies to various nucleolar and ribosomal proteins, we define, by immunolocalization in situ, the distribution of nucleolar proteins in the different morphological nucleolar subcompartments. In the present study we describe the nucleolar localization of a specific ribosomal protein (51) by immunofluorescence and immunoelectron microscopy using a monoclonal antibody (R5 1-105). In immunoblotting experiments, this antibody reacts specifically with the largest and most acidic protein of the small ribosomal subunit (51) and shows wide interspecies cross-reactivity from amphibia to man. Beside its localization in cytoplasmic ribosomes, this protein is found to be specifically localized in the granular component of the nucleolus and in distinct granular aggregates scattered over the nucleoplasm. This indicates that ribosomal protein 51, in contrast to reports on other ribosomal proteins, is not bound to nascent pre-rRNA transcripts but attaches to preribosomes at later stages of rRNA processing and maturation. This protein is not detected in the residual nucleolar structures of cells inactive in rRNA synthesis such as amphibian and avian erythrocytes. During mitosis, the nucleolar material containing ribosomal protein 51 undergoes a remarkable transition and shows a distribution distinct from that of several other nucleolar proteins. In prophase, the nucleolus disintegrates and protein 51 appears in numerous small granules scattered throughout the prophase nucleus. During metaphase and anaphase, a considerable amount of this protein is found in association with the surfaces of all chromosomes and finely dispersed in the cell plasm. In telophase, protein 51-containing material reaccumulates in granular particles in the nucleoplasm of the newly formed nuclei and, finally, in the re-forming nucleoli. These observations indicate that the nucleolus-derived particles containing ribosomal protein 51 are different from cytoplasmic ribosomes and, in the living cell, are selectively recollected after mitosis into the newly formed nuclei and translocated into a specific nucleolar subcompartment, i.e ., the granular component. The nucleolar location of ribosomal protein 51 and its rearrangement du'ring mitosis is discussed in relation to the distribution of other nucleolar proteins. KW - Cytologie Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39695 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Sommerville, John A1 - Müller, Ulrike T1 - DNA is assembled into globular supranucleosomal chromatin structures by nuclear contents of amphibian oocytes N2 - The assembly of DNA into nucleosomal and supranucleosomal chromatin structures has been studied (i) by injection of circular DNA molecules (plasmids) into nuclei of Pleurodeles waltlii oocytes; and (ii) by in vitro incubation of plasmid molecules with the supernatant fraction from oocyte nuclei of Pleurodeles and Xenopus laevis, followed by purification of nucleoprotein structures formed with sucrose gradient centrifugation. [n both types of experiments , spread preparations of the newly assembled and transcriptionally inactive chromatin , examined by electron microscopy , show dense globular higher order (supranucleosomal) packing forms. Under partially relaxing (low salt) preparation conditions granular chromatin subunits of about 30 nm diameter can be seen either as widely spaced particles or in closely packed aggregates. The transcriptionally inactive endogenous chromatin of chromomeres of lampbrush chromosomes is arranged in similar higher order chromatin units. A correlation is found between the sizes of the DN A molecule probes used and the numbers of nucleosomes and higher order globules in the assembled chromatin structures. After prolonged dispersion in low salt buffers , these globular chromatin units unfold into chains of7-12 nucleosomes. The results support the concept that chromatin is arranged , under physiological ion concentrations as they are present in the nucleus , in supranucleosomal units of globular morphology. Y1 - 1980 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39671 ER - TY - JOUR A1 - Franke, Werner W. A1 - Kartenbeck, Jürgen A1 - Krien, S. A1 - VanderWoude, W. J. A1 - Scheer, Ulrich A1 - Morré, D. J. T1 - Inter- and intracisternal elements of the Golgi apparatus: A system of membrane-to-membrane cross-links N2 - Electron opaque cross-bridge structures span the inter- and intracisternal spaces and provide membrane-to-membrane connections between adjacent cisternae of dictyosomes of pollen tubes of Clivia and Lilium. Additionally, the classic intercisternal rods, characteristic of intercisternal regions near the maturing face of dictyosomes, are connected with the adjacent membranes through similar cross-bridge elements. We suggest that these structural links are responsible for maintaining the flattened appearance of the central parts of Golgi apparatus cisternae as well as for the coherence of cisternae within the stack. Observations on other plant (e.g. microsporocytes of Canna) and animal cells (e.g. rodent liver and hepatoma cells, newt spermatocytes) show that such an array of membrane cross-links is a universal feature of Golgi apparatus architecture. The cross-bridges appear as part of the complex "zone of exclusion" which surrounds dictyosomes, entire Golgi apparatus and Golgi apparatus equivalents in a variety of cell types. KW - Golgi apparatus KW - Membranes KW - Cross-bridges KW - Electron microscopy Y1 - 1972 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39514 ER - TY - JOUR A1 - Scheer, Ulrich T1 - The ultrastructure of the nuclear envelope of amphibian ooctyes: IV. On the chemical nature of the nuclear pore complex material N2 - In order to investigate the chemical composition of the nuclear pore complexes isolated nuclei from mature Xenopus laevis oocytes were manually fractioned into nucleo· plasmic aggregates and the nuclear envelopes. The whole isolation procedure takes no more than 60- 90 sec, and the pore complexes of the isolated envelopes are well preserved as demonstrated by electron microscopy. Minor nucleoplasmic and cytoplasmic contaminations associated with the isolated nuclear envelopes were determined with electron microscopic morphometry and were found to be quantitatively negligible as far as their mass and nucleic acid content is concerned. The RNA content of the fractions was determined by direct phosphorus analysis after differential alkaline hydrolysis. Approximately 9% of the total nuclear RNA of the mature Xenopus egg was found to be attached to the nuclear envelope. The nonmembranous elements of one pore complex contain 0.41 X 10- 16 g RNA. This value agrees well with the content estimated from morphometric data. The RNA package density in the pore complexes (270 X 10- 15 g/fJ-3) is compared with the nucleolar, nucleoplasmic and cytoplasmic RNA concentration and is discussed in context with the importance of the pore complexes for the nucleo-cytoplasmic transport of RNA-containing macromolecules. Additionally, the results of the chemical analyses as well as of the 3H-actinomycin D autoradiography and of the nucleoprotein staining method of Bernhard (1969) speak against the occurence of considerable amounts of DNA in the nuclear pore complex structures. KW - Nuclear envelope KW - Amphibian oocytes KW - Nuclear pore complex KW - Chemical nature KW - Electron microscopy Y1 - 1972 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39500 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Herth, Werner T1 - Cytology, general and molecular cytology N2 - The present article had originally been conceived as a review on endomembranes, the plasma membrane, and the major product of membrane-bound activities, the cell wall material. However, limitations of space and the cascading number of pertinent literature articles made it necessary to confine this to one group of membranes and one type of cell wall components. Therefore, we shall begin our survey on the biochemical and cytological aspects of membranes by a review of the class of the pore complex bearing endomembranes, i.e. the nuclear envelope and the annulate lamellae (AL). Next year the membranes of the endoplasmic reticulum and the dictyosomes will be dealt with in conjunction with a discussion of the various intracellular vesicles, the tonoplast and the plasmalemma. KW - Botanik Y1 - 1974 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39499 ER - TY - CHAP A1 - Franke, Werner W. A1 - Zentgraf, Hanswalter A1 - Scheer, Ulrich T1 - Supranucleosomal and non-nucleosomal chromatin configurations N2 - A significant contribution to the understanding of chromatin organization was the d iscovery of the nucleosome as a globular repeating unit of the package of DNA (Hewish and Burgoyne, 1973; Woodcock, 1973; Kornberg, 1974; Olins and Olins, 1974; for review see Oudet et al., 1978 a) . In accord with the original definition and in ag reement with most workers in this field of research we identify a nucleosome as a spheric alor slightly oblate gr anular particle 10-13 nm in diameter, containing about 200 base pairs of DNA and two of each of the four his tones H2a, H2b, H3 and H4. It is this structure in which the bulk of the nuclear chroma tin is organized in most eukaryotic cells, with the exception of the dinofl age llates (Rae and Steele, 1977; dinofl agellate DNA, however, c an be packed into nucleosoma l structures in vitro by addition of the appropriate amounts of histones;the same reference). Although it seems clear from the work reported that condensed and transcriptiona lly inactive chroma tin is contained in nucleosomes as the principle for first order p acking of DNA there are two important questions onto which we are focusing in the present study: ( i ) What is the higher order of p a cking present in - and perhaps typical-of - the condensed sta te of chromatin, and (ii) what is the specific form of arrangement of transcriptionally a ctive chromatin? Y1 - 1978 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39447 ER - TY - CHAP A1 - Scheer, Ulrich T1 - Electron microscopic analysis of chromatin and gene expression N2 - No abstract available Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39456 ER - TY - JOUR A1 - Knecht, Sigrid A1 - Scheer, Ulrich T1 - Lautäußerung und Verhalten des Azoren-Buchfinken (Fringilla coelebs moreletti Pucheran) N2 - Einleitung und Methode S. 155. - Brutbiologie S. 155. - Motivgesang S. 157. - Sozialruf (Social Call) S. 161. - Entwicklung des Sozialrufs S. 164. - Brumimmungsruf (Regenruf) S. 165. - Flugruf S. 166. - Alarmruf eines Jungvogels S. 167. - Bestimmung der ReviergroBe S. 167. - Zusammenfassung S. 168. - Summary S. 168. - Literaturverzeichnis S. 169. Es wird untersucht, ob die Azoren-Buchfinken "Rassengesang" und "Rassenrufe" haben. Gesange und Rufe wurden auf Tonband aufgenommen und klangspek trogra phiert. Motivgesang. Jedes cJ beherrscht 2-6 verschiedene Gesangsformen, wobei stets eine "Alltagsform" mit der stark vereinfachten Phrase di-djah endigt. Die anderen, weniger haufigeren Gesangsformen ("Sonntagsformen") zeigen eine besser ausgearbeitete Endphrase, die jedoch nie so kompliziert wie bei kontinentalen Buchfinken ist. In Gebieten, in denen sich bevorzugt Kanarienvogel aufhalten, konnen Buchfinken Gesangselemente iibernehmen. Sozialruf. Das kontinentale pink ist auf alIen Azoreninseln durch ga ersetzt, so daB man von einem Rassenruf sprechen kann. Er ist mit starker Aggressionsneigung verkniipft. Der Sozialruf zeigt einen weiten Frequenzumfang, hervorgerufen durch mehrere simultane Noten. Brutstimmungsruf (Regenruf). Eine Anzahl verschiedener Rufe wurde spektrographiert. Vom cJ ist er bei maBiger Gefahr, aber auch spontan (30-70 Rufe/Min.) zu horen. Flugruf. Er scheint mit dem Flugruf der Nominatform identisch zu sein. Bestimmung der Reviergrope. Ein cJ wurde innerhalb seines Reviers an die "akustische Leine" genommen und bis zu den Reviergrenzen gezogen. Verhalten und LautauBerung anderten sich in Abhangigkeit von der jeweiligen Entfernung bis zur Reviergrenze. N2 - The attempt was made to determine whether Azores chaffinches possess a "racial song" or "racial calls". The songs and calls were tape-recorded and sound-spectrographs were prepared. 1. The song motif. Each cJ possesses 2-6 different song types, among which there is an "everyday type" which always ends with the greatly simplified phrase: dee-chah. The other, less frequent song types ("Sunday types") exhibit a more developed final phrase, though this is not as complex as that of Continental chaffinches. In areas where canaries commonly occur, chaffinches may adopt some of their song elements. 2. The social call. The Continental pink is replaced by gai in all of the Azores island forms, so it is justifiable to speak of a "racial call". This call is correlated with a strong aggressive tendency; it exhibits a broad frequency range based upon simultaneous utterance of several notes. 3. The brooding call ("rain-call"). A number of different calls were spectrographed. With the cJ, this call can be heard in response to mild danger and also as a spontaneous utterance (30-70 calls /min.). 4. Flight call. This seems to be identical to the flight call of the nominate type. 5. Determination of territory size. A cJ was led within his territory on an "acoustical lead" and drawn to his territorial boundaries. His. behaviour and vocalizations altered in relation to the distance from the territorial boundary. KW - Tierpsychologie Y1 - 1968 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39479 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Benavente, Ricardo T1 - Functional and dynamic aspects of the mammalian nucleolus N2 - Nucleoli are the sites of ribosome biogenesis. Transcription of the ribosomal RNA genes as well as processing and initial packaging of their transcripts with ribosomal and non-ribosomal proteins all occur within the nucleolus in an ordered manner and under defined topological conditions. Components of the nucleolus have been localized by immunocytochemistry and their functional aspects investigated by microinjection of antibodies directed against the enzyme responsible for rDNA transcription, RNA polymerase I. The role of nascent transcripts in postmitotic formation of nucleoli will be discussed. Y1 - 1990 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34269 ER - TY - CHAP A1 - Dabauvalle, M.-C. A1 - Wilken, N. A1 - Ewald, A. A1 - Kuhbier, A. A1 - Senécal, J.-L. A1 - Scheer, Ulrich T1 - Nuclear pore complex structure analyzed by immunogold EM with human autoantibodies N2 - No abstract available Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39439 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Weisenberger, Dieter T1 - The nucleolus N2 - No abstract available Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32037 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Rose, Kathleen M. T1 - Localization of RNA polymerase I in interphase cells and mitotic chromosomes by light and electron microscopic immunocytochemistry N2 - Rabbit antibodies to RNA polymerase I from a rat hepatoma have been used to localize the enzyme in a variety of cells at the light and electron microscopic level. In interphase cells the immunofluorescence pattern indicated that polymerase I is contained exclusively within the nucleolus. That this fluorescence, which appeared punctated rather than uniform, represented transcriptional complexes of RNA polymerase I and rRNA genes was suggested by the observation that it was enhanced in regenerating liver and in a hepatoma and was markedly diminished in cells treated with actinomycin D. Electron microscopic immunolocalization using gold-coupled second antibodies showed that transcribed rRNA genes are located in, and probably confined to, the fibrillar centers of the nucleolus. In contrast, the surrounding dense fibrillar component, previously thought to be the site of nascent prerRNA, did not contain detectable amounts of polymerase I. During mitosis, polymerase I molecules were detected by immunofluorescence microscopy at the chromosomal nucleolus organizer region, indicating that a considerable quantity of the enzyme remains bound to the rRNA genes. From this we conclude that rRNA genes loaded with polymerase I molecules are transmitted from one cell generation to the next one and that factors other than the polymerase itself are involved in the modulation of transcription of DNA containing rRNA genes during the cell cycle. KW - nucleolus KW - nucleolus organizer KW - fibrillar centers KW - rRNA genes KW - anti-RNA polymerase I antibodies Y1 - 1984 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33223 ER - TY - JOUR A1 - Zentgraf, Hanswalter A1 - Trendelenburg, Michael F. A1 - Spring, Herbert A1 - Scheer, Ulrich A1 - Franke, Werner W. A1 - Müller, Ulrike A1 - Drury, Kenneth C. A1 - Rungger, Duri T1 - Mitochondrial DNA arranged into chromatin-like structures after injection into amphibian oocyte nuclei N2 - Purified mitochondrial DNA (mitDNA) from ovaries ofXenopus lae vis was injected into the nuclei (germinal vesicles) of large viteUogenic oocytes of the same organism and examined by electron microscopy ofthe spread nuclear contents. Normally located nuclei of untreated oocytes as weil as peripherally translocated nuclei of centrifuged oocytes were used. In addition, oocyte nuclei isolated and incubated under liquid paraffin oil were injected with DNA. The integrity oftranscriptional structures of endogenous chromosomal (Iampbrush chromosomes) and extrachromosomal (nucleoli) genes of the injected nuclei was demonstrated. Microinjected mitDN A was identified as circles of chromatin exhibiting polynucleosome-like organization and a me an contour length of 2.6 J.Lm, corresponding to a compaction ratio of the mitDN A of about 2 : I. This DNA packing ratio is similar to that observed after preparation of various kinds of native chromatin in low salt buffers. The chromatin circles formed from injected mitDNA only very rarely exhibited lateral fibrils suggestive of transcriptional activity. These results suggest that purified mitDNA can be transformed to normally structured chromatin when exposed to oocyte nuclear contents but is rarely , if at all , transcribed in this form and in this environment. Y1 - 1979 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33174 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Hügle, Barbara A1 - Hazan, Rachel A1 - Rose, Kathleen M. T1 - Drug-induced dispersal of transcribed rRNA genes and transcriptional products: Immunolocalization and silver staining of different nucleolar components in rat cells treated with 5,6-dichloro-1-Beta-D-ribofuranosylbenzimidazole N2 - Upon incubation of cultured rat cells with the adenosine analogue 5,6-dichloro-l-β- D-ribofuranosylbenzimidazole (DRB), nucleoli reversibly dissociate into their substructures, disperse throughout the nuclear interior, and form nucleolar "necklaces". We have used this experimental system, which does not inhibit transcription of the rRNA genes, to study by immunocytochemistry the distribution of active rRNA genes and their transcriptional products during nucleolar dispersal and recovery to normal morphology. Antibodies to RNA polymerase I allow detection of template-engaged polymerase, and monoclonal antibodies to a ribosomal protein (S 1) of the small ribosomal subunit permit localization of nucleolar preribosomal particles. The results show that, under the action of DRB transcribed rRNA, genes spread throughout the nucleoplasm and finally appear in the form of several rows, each containing several (up to 30) granules positive for RNA polymerase land argyrophilic proteins. Nucleolar material containing preribosomal particles also appears in granular structures spread over the nucleoplasm but its distribution is distinct from that of rRNA gene-containing granules. We conclude that, although transcriptional units and preribosomal particles are both redistributed in response to DRB, these entities retain their individuality as functionally defined subunits. We further propose that each RNA polymerase-positive granular unit represents a single transcription unit and that each continuous array of granules ("string of nucleolar beads") reflects the linear distribution of rRNA genes along a nucleolar organizer region. Based on the total number of polymerase I-positive granules we estimate that a minimum of 60 rRNA genes are active during interphase of DRB-treated rat cells. Y1 - 1984 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33216 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Lanfranchi, Gerolamo A1 - Rose, Kathleen M. A1 - Franke, Werner W. A1 - Ringertz, Nils R. T1 - Migration of rat RNA polymerase I into chick erythrocyte nuclei undergoing reactivation in chick-rat heterokaryons N2 - Transcriptionally inactive chick erythrocyte nudei were reactivated by Sendai virusinduced fusion of erythrocytes with rat L6j1 myoblasts. We used antibodies to trace the appearance of a specific protein engaged in transcription of a defined dass of genes, those coding for rRNA, during reactivation. Using immunofluorescence microscopy, we found increasing amounts of rat RNA polymerase I to appear, during a certain period of time after fusion, in the reforming nudeoli of the chick nudei. Amounts of rat RNA polymerase I sufficient to be detected by immunofluorescence microscopy had accumulated in the newly developed chick nudeoli 72- 190 h after fusion was initiated. This time interval coincides with the time when chick rRNA synthesis can first be detected. The results raise the possibility that during these stages of the reactivation process chick rRNA genes are transcribed by heterologous RNA polymerase I moleeules of rat origin. Y1 - 1983 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33232 ER - TY - CHAP A1 - Zentgraf, Hanswalter A1 - Scheer, Ulrich A1 - Franke, Werner W. T1 - On the existence of arrested transcriptional machinery in late stages of avian erythropoiesis N2 - No abstract available Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33696 ER - TY - CHAP A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - Pathways of nucleocytoplasmic translocation of ribonucleoproteins N2 - No abstract available Y1 - 1974 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33832 ER - TY - CHAP A1 - Trendelenburg, M. F. A1 - Franke, Werner W. A1 - Spring, H. A1 - Scheer, Ulrich T1 - Ultrastructure of transcription in the nucleoli of the green algae Acetabularia major and A. mediterranea N2 - No abstract available Y1 - 1975 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33779 ER - TY - CHAP A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - Biochemical and structural aspects of nucleocytoplasmic transfer of ribonucleoproteins at the nuclear envelope level: facts and theses N2 - No abstract available Y1 - 1975 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33766 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Trendelenburg, M. F. A1 - Franke, Werner W. T1 - Regulation of transcription of ribosomal RNA genes during amphibian oogenesis N2 - No abstract available Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33700 ER - TY - JOUR A1 - Dabauvalle, Marie-Christine A1 - Schulz, Barbara A1 - Scheer, Ulrich A1 - Peters, Reiner T1 - Inhibition of nuclear accumulation of karyophilic proteins in living cells by microinjection of the lectin wheat germ agglutinin N2 - No abstract available Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34288 ER - TY - JOUR A1 - Rungger, M. A1 - Crippa, M. A1 - Trendelenburg, M. F. A1 - Scheer, Ulrich A1 - Franke, Werner W. T1 - Visualization of rDNA spacer transcription in Xenopus oocytes treated with fluorouridine N2 - Under the intluence of 5-tluoro-uridine, the ultrastructure of the rDNA transcription units in Xenopus oocytes is altered. Whereas part of the matrix units maintains anormal aspect or shows various degrees of inhibition, in a strong proportion of the transcription units the alternating pattern of matrix units and fibril-free spacer regions is no longer recognized. Transcriptional complexes are found along the entire DNP axis, including the regions of the spacers. These observations support biochemical data on transcription in rDNA spacer region. Y1 - 1978 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33082 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Sommerville, John T1 - Sizes of chromosome loops and hnRNA molecules in oocytes of amphibia of different genome sizes N2 - The lengths of lampbrush chromosome loops and their tran scription units show a positive correlation with genome size in oocytes of amphibia with different C values. However, there is no such correlation with contour lengths of hnRNA molecu les isolated from these oocytes. These results indi cate th at more ON A sequences are transcribed in amphibia of higher C value , but that processing of RNA transc ripts occurs while they are still attached to the chromosomes as nascent ribonucleoprotein fibrils. Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33094 ER - TY - JOUR A1 - Krohne, Georg A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - The major polypeptides of the nuclear pore complex N2 - Nuclear envelopes of maturing oocytes of various amphibia contain an unusually high number of pore complexes in very close packing. Consequently, nuclear envelopes , which can be manually isolated in great purity, provide a remarkable enrichment of nuclear pore complex material, relative to membranous and other interporous structures. When the polypeptides of nuclear envelopes isolated from oocytes of Xenopl/s la evis and Triturus alpestris are examined by gel electrophoresis, visualized either by staining with Coomassie blue or by radiotluorography after in vitro reaction with [3H]dansyl chloride , a characteristic pattern is obtained (10 major and 15 minor bands). This polypeptide pattern is radically different from that of the nuclear contents isolated from the same cell. Extraction of the nuclear envelope with high salt concentrations and moderateIy ac tive detergents such as Triton X- 100 results in the removal of membrane material but leaves most of the non-membranous structure of the pore complexes. The dry weight of the pore complex (about 0.2 femtograms) remains essentially unchanged during such extractions as measured by quantitative electron microscopy . The extracted preparations which are highly enriched in nuclear pore complex material contain only two major polypeptide components with apparent molecular weights of 150000 and 73000. Components of such an electrophoretic mobility are not present as major bands , if at all , in nuclear contents extracted in the same way. lt is concluded that these two polypeptides are the major constituent protein(s) of the oocyte nuclear pore complex and are specific for this structure. When nuclear envelopes are isolated from rat liver and extracted with high salt buffers and Triton X- 100 similar bands are predominant, but two additional major components of molecular weights of 78000 and 66000 are also recognized. When the rat liver nuclear membranes are further subfractionated material enriched in the 66000 molecular weight component can be separated from the membrane material, indicating that this is relatively loosely associated material , probably a part of the nuclear matrix . The results suggest that the nuclear pore complex is not only a characteristic ubiquitous structure but also contains similar, if not identical , skeletal proteins that are remarkably re sistant to drastic changes of ionic strength as weil as to treatments with detergents and thiol reagents. Y1 - 1978 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33078 ER - TY - JOUR A1 - Hadjiolova, Krassimira A1 - Rose, Kathleen M. A1 - Scheer, Ulrich T1 - Immunolocalization of nucleolar proteins after D-galactosamine-induced inhibition of transcription in rat hepatocytes N2 - No abstract available Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33205 ER - TY - JOUR A1 - Moreno-Diaz de la Espina, Susana A1 - Franke, Werner W. A1 - Krohne, Georg A1 - Trendelenburg, Michael F. A1 - Grund, Christine A1 - Scheer, Ulrich T1 - Medusoid fibril bodies: a novel type of nuclear filament of diameter 8 to 12 nm with periodic ultrastructure demonstrated in oocytes of Xenopus laevis N2 - No abstract available Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34116 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - The ultrastructure of the nuclear envelope of amphibian oocytes: a reinvestigation. I. The mature oocyte N2 - 1 n order to review the contradictory statements on the ultrast ructure of the nuclear envelope, a study was undertaken combining section and negat ive stai ning electron microscopy on manually isolated oocyte nuclei and nuclear envelopes from six amphibian species including Anura as well as Urodela. The a ppeara nce of the negatively stained iso lated nuclear envelopes is described in deta il and the dependence on the preparation co nditions used is emphas ized . Pore complex structures such as pore perimeter, central granule, an nul ar components, interna l fibrils, and annu lus-attached fibrils could be identified by both techniques, negat ive staining and sect ions. Comparative studies show that no marked diffe rences ex ist in the structural data of the nuclear envelope among the investigated amphibians and the significance of the structural components is discussed. A model of the nuclea r pore complex based on the findings of the present investigation is prese nted. Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-32098 ER - TY - JOUR A1 - Zentgraf, H. A1 - Müller, U. A1 - Scheer, Ulrich A1 - Franke, W. W. T1 - Evidence for the existence of globular units in the supranucleosomal organization of chromatin N2 - No abstract available Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34123 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Trendelenburg, Michael F. A1 - Krohne, Georg A1 - Franke, Werner W. T1 - Lengths and patterns of transcriptional units in the amplified nucleoli of oocytes of Xenopus laevis N2 - Transcriptionally active chromatin from peripheral amplified nuc1eoli of lampbrush-chromosome stage oocytes of Xenopus laevis was dispersed and spread in various solutions of low salt concentrations (incIuding some with additions of detergents) and examined by electron microscopy. Nucleolar material from oocytes of animals with normal (2-nu) and mutant (I-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 c1asses of 3.3 and 3.8 11m 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 labelIed pre-rRNA under non-denaturing and denaturing conditions. Evaluations of individual strands of nucleolar chromatin furt her 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. Y1 - 1977 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33069 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Zentgraf, Hanswalter T1 - Nucleosomal and supranucleosomal organization of transcriptionally inactive rDNA circles in Dytiscus oocytes N2 - 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 eta!. , 1976). When similar preparations are made from previtellogenic ooytes in which a large proportion of the nuc1eolar 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. Nuc1eosomal packing is also indicated by the comparison of the lengths of these chromatin rings with both iso lated rDNA circ1es and transcribed chromatin rings. In addition, these inactive nuc1eofilaments often appear to be compacted into globular higher order structures of diameters from 21 to 34nm, each composed of an aggregate of 6-9 nuc1eosomes. 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 nuc1eosomal state it is 10- 13 fold when supranuc1eosomal globules are present. These data show that the extrachromosomal rDNA of these oocytes goes through a cycle of condensation and extensio n, as a function of the specific transcriptional activity, and that the beaded state described here is exc1usively found in the non-transcribed state. Y1 - 1978 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33188 ER - TY - JOUR A1 - Trendelenburg, Michael F. A1 - Scheer, Ulrich A1 - Zentgraf, Hanswalter A1 - Franke, Werner W. T1 - Heterogeneity of spacer lengths in circles of amplified ribosomal DNA of two insect species, Dytiscus marginalis and Acheta domesticus N2 - No abstract available Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33055 ER - TY - JOUR A1 - Bona, Marion A1 - Scheer, Ulrich A1 - Bautz, Ekkehard K. F. T1 - Antibodies to RNA polymerase II (B) inhibit transcription in lampbrush chromosomes after microinjection into living amphibian oocytes N2 - Antibodies directed against RNA polymerase II (B) from Drosophila melanogaster were obtained from rabbit sera and, as monoclonal immunoglobulins, from mouse hybridomas and shown to cross-react with the amphibian enzyme protein. Localization by indirect immunofluorescence microscopy revealed the association of this enzyme with chromatin of interphase nuclei of amphibian cells and its absence in nucleoli. Purified immunoglobulins were microinjected in to nuclei ofliving vitellogenic oocytes of Ple1lrodeles waltlii and X enopus laevis and their effects on transcriptional processes were monitored by biochemical and light and electron microscopic stud ies. RNA polymerase II antibodies from rabbit sera caused a rapid and almost complete release of nascent transcripts from the chromatin axis of the loops of lampbrush chromosomes, followed by collapse of the loops and their retraction on the main chromosome axis. Monoclonal murine antibodies to the Iarge RNA polymerase II subunits also inhibited transcription in chromosome Ioops but appeared to inhibit initiation rather than elongation events. Activities of class land III RNA polymerases were not significantly affected by injection of antibodies to polymerase II, indicating immunological differences between the three RNA polymerases. The potential value of the in vitro test system described , as a very sensitive assay for detecting proteins involved in transcription in living cells, is discussed. 1 Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33128 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Krohne, Georg A1 - Jarasch, Ernst-Dieter T1 - The nuclear envelope and the architecture of the nuclear periphery N2 - No abstract available Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33108 ER - TY - JOUR A1 - Franke, Werner W. A1 - Kleinschmidt, Jürgen A. A1 - Spring, Herbert A1 - Krohne, Georg A1 - Grund, Christine A1 - Trendelenburg, Michael F. A1 - Stöhr, Michael A1 - Scheer, Ulrich T1 - A nucleolar skeleton of protein filaments demonstrated in amplified nucleoli of Xenopus laevis N2 - The amplified, extrachromosomal nucleoli of Xenopus oocytes contain a meshwork of -4-nm-thick filaments, which are densely coiled into higher-order fibrils of diameter 30-40 nm and are resistant to treatment with high- and low-salt concentrations, nucleases (DNase I, pancreatic RNase, micrococcal nuclease), sulfhydryl agents, and various nonionic detergents. This filamentous "skeleton" has been prepared from manually isolated nuclear contents and nucleoli as weil as from nucleoli isolated by fluorescence-activated particle sorting. The nucleolar skeletons are observed in light and electron microscopy and are characterized by ravels of filaments that are especially densely packed in the nucleolar cortex. DNA as weil as RNA are not constituents of this structure, and precursors to ribosomal RNAs are completely removed from the extraction-resistant filaments by treatment with high-salt buffer or RN ase. Fractions of isolated nucleolar skeletons show specific enrichment of an acidic major protein of 145,000 mol wt and an apparent pi value of -6.15, accompanied in some preparations by various amounts of minor proteins. The demonstration of this skeletal structure in "free" extrachromosomal nucleoli excludes the problem of contaminations by nonnucleolar material such as perinucleolar heterochromatin normally encountered in studies of nucleoli from somatic cells. It is suggested that this insoluble protein filament complex forms a skeleton specific to the nucleolus proper that is different from other extraction-resistant components of the nucleus such as matrix and lamina and is involved in the spatial organization of the nucleolar chromatin and its transcriptional products. In studies of the organization of the interphase nucleus, considerable progress has been made in the elucidation of the arrangement of chromatin components and transcriptional products. However, relatively little is known about the composition and function of another category of nuclear structures, the nonnucleoproteinaceous architectural components that are insoluble in solutions of low and high ionic strength, despite numerous studies dedicated to this problem. Such structures include (a) the nuclear envelope and its pore complexes (I, 15, 18, 23, 37, 41), (b) a peripheral layer of insoluble protein ("lamina"; I, 15, 22, 23, 59), (e) certain skeletal proteins related to the chromosome "scaffold" described by Laemmli and coworkers (see references 2 and 3), and (d) ill-defined tangles of fibrillar structures of the nuclear interior that are collectively described as residual "matrix" (6, 21 ; for reviews, see references THE JOURNAL OF CEll BrOlOGY . VOlUME 90 AUGUST 1981 289-299 © The RockefeIler University Press · 0021 -9525/ 81 / 08/ 0289/ 11 $1 .00 4 and 12). The latter, preparatively Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33130 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Identification of a novel class of tandemly repeated genes transcribed on lampbrush chromosomes of Pleurodeles waltlii N2 - Electron microscope preparations of lampbrush chromosomes from oocytes of Pleurodeles waltl;; have revealed a new class of tandemly repeated genes. These genes are highly active, as judged by the close spacing of nascent transcripts. They occur in clusters of >100 copies and are transcribed in units containing roughly 940 base pairs of DNA that are separated by nontranscribed spacers of an estimated DNA content of 2,410 base pairs. The size and the pattern of arrangement of these transcription units can not be correlated with any of the repetitious genes so far described. Y1 - 1981 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33153 ER - TY - JOUR A1 - Bell, Peter A1 - Dabauvalle, Marie-Christine A1 - Scheer, Ulrich T1 - In vitro assembly of prenucleolar bodies in Xenopus egg extract N2 - Nuclei assembled in Xenopus egg extract from purified DNA or chromatin resemble their natural counterparts in a number of structural and functional features. However, the most obvious structural element of normal interphase nuclei, the nucleolus, is absent from the in vitro reconstituted nuclei. By EM, cytological silver staining, and immunofluorescence microscopy employing antibodies directed against various nucleolar components we show that nuclei assembled in vitro contain numerous distinct aggregates that resemble prenucleolar bodies (PNBs) by several criteria. Formation of these PNB-like structures requires pore complex-mediated nuclear transport of proteins but is independent of the genetic content of the in vitro nuclei as well as transcriptional and translational events. Our data indicate that nuclei assembled in vitro are capable of initiating early steps of nucleologenesis but that the resulting PNBs are unable to fuse with each other, probably due to the absence of a functional nucleolus organizer. With appropriate modifications, this experimental system should be useful to define and analyze conditions promoting the site-specific assembly of PNBs into a coherent nucleolar body. Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34233 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Dabauvalle, Marie-Christine A1 - Merkert, Hilde A1 - Benavente, Ricardo T1 - The nuclear envelope and the organization of the pore complexes N2 - No abstract available Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34275 ER - TY - JOUR A1 - Reinhard, Matthias A1 - Halbrügge, Maria A1 - Scheer, Ulrich A1 - Wiegand, Christiane A1 - Jockusch, Brigitte M. A1 - Walter, Ulrich T1 - The 46/50 kDa phosphoprotein VASP purified from human platelets is a novel protein associated with actin filaments and focal contacts N2 - Vasoactive agents which elevate either cGMP or cAMP inhibit platelet activation by pathways sharing at least one component, the 46/50 kDa vasodilator-stimulated phosphoprotein (V ASP). V ASP is stoichiometrically phosphorylated by both cGMP-dependent and cAMPdependent protein kinases in intact human platelets, and its phosphorylation correlates very well with platelet inhibition caused by cGMP- and cAMP-elevating agents. Here we report that in human platelets spread on glass, V ASP is associated predominantly with the distal parts of radial micro filament bundles and with microfilaments outlining the periphery, whereas less V ASP is associated with a central microfilamentous ring. V ASP is also detectable in a variety of different cell types including fibroblasts and epithelial cells. In fibroblasts, V ASP is concentrated at focal contact areas, along microfilament bundles (stress fibres) in a punctate pattern, in the periphery of protruding lamellae, and is phosphorylated by cGMP- and cAMP-dependent protein kinases in response to appropriate stimuli. Evidence for the direct binding of V ASP to F -actin is also presented. The data demonstrate that V ASP is a novel phosphoprotein associated with actin filaments and focal contact areas, i.e. transmembrane junctions between microfilaments and the extracellular matrix. KW - cAMP / cGMP / cytoskeleton / phosphorylation / protein kinase Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34246 ER - TY - JOUR A1 - Reimer, Georg A1 - Rose, Kathleen M. A1 - Scheer, Ulrich A1 - Tan, Eng M. T1 - Autoantibody to RNA polymerase I in scleroderma sera N2 - Autoantibodies to components of the nucleolus are a unique serological feature of patients with scleroderma. There are autoantibodies of several specificities; one type produces a speckled pattern of nucleolar staining in immunofluorescence. In actinomycin D and 5,6-dichloro-{j-D-ribofuranosylbenzimidazoletreated Vero cells, staining was restricted to the fibrillar and not the granular regions. By double immunofluorescence, specific rabbit anti-RNA polymerase I antibodies stained the same fibrillar structures in drug-segregated nucleoli as scleroderma sera. Scleroderma sera immunoprecipitated 13 polypeptides from (35S)methionine-labeled HeLa cell extract with molecular weights ranging from 210,000 to 14,000. Similar polypeptides were precipitated by rabbit anti-RNA polymerase I antibodies, and their common identities were confirmed in immunoabsorption experiments. Microinjection of purified IgG from a patient with speckled nucleolar staining effectively inhibited ribosomal RNA transcription. Autoantibodies to RNA polymerase I were restricted to certain patients with scleroderma and were not found in other autoimmune diseases. Y1 - 1987 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-34294 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Sommerville, John A1 - Bustin, M. T1 - Injected histone antibodies interfere with transcription of lampbrush chromosome loops in oocytes of Pleurodeles N2 - Antibodies to calf thymus histone H2B were purified by chromatography on DEAE-cellulose and injected into oocyte nuclei of Pleurodeles waltlii. As shown by indirect immunofluorescence these antibodies cross-reacted strongly with corresponding histones associated with lampbrush chromosomes. Shortly after injection the lateral loops of the chromosomes retracted into the chromomeres and by 3 h postinjection the 'lampbrush' appearance was completely lost and the chromosomes appeared in light-microscopic preparations as rod-like structures consisting of 10ngitudina11y coalesced chromomeres. In control oocytes injected with non-immune immunoglobulins or antibodies against a ubiquitous transcript-associated protein no morphological alterations of the lampbrush chromosomes could be observed. Electron microscopic spreads of chromosomes prepared at various times after injection of anti-H2B revealed a progressive loss of transcriptional complexes from the loop axes. Finally, higher-order chromatin configurations, like supranuc1eosomal globules (' superbeads ') or cable-like chromatin strands 50- 60 nm thick predominated, indicating complete transcriptional inactivation of a11 chromosomal regions. The results indicate that H2B antibodies react specifically with his tones associated with the transcribed DNA of lateral loops in their native state. The resulting antigenantibody complexes seem to inhibit progression of the R A polymerases along the template, thus causing the premature release of transcripts, a process analogous to the stripping effect of actinomycin D. The demonstration of histones associated with heavily transcribed regions, which are not compacted into nucleosomes but largely extended, supports the current concept that unfolding of nucleosomes to a110w transcription of the DNA does not involve dissociation of histones. In contrast, amplified ribosomal RNA genes are unaffected by injected HzB antibodies. This does not necessarily indicate absence of his tones from nucleolar chromatin, since we do not know whether it is accessible in vivo to antibodies or whether the histone antigenie determinants are masked by the presence of other proteins. The technique of injecting specific antibodies should be widely applicable when analysing the in vivo distribution of chromosomal components at the electron-microscopic level and when studying complex metabolie processes, like the cleavage and modification of RNA, by selective inhibition of defined enzymic steps. Y1 - 1979 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33166 ER - TY - JOUR A1 - Reimer, Georg A1 - Scheer, Ulrich A1 - Peters, Jan-Michael A1 - Tan, Eng M. T1 - Immunolocalization and partial characterization of a nucleolar autoantigen (PM-Scl) associated with polymyositis / scleroderma overlap syndromes. N2 - Precipitating anti-PM-Sel antibodies are present in sera from patients with polymyositis. scleroderma. and polymyositis/scleroderma overlap syndromes. By indirect immunofluorescence microscopy. anti-PM-Scl antibodies stained the nucleolus in cells of different tissues and species. suggesting that the antigen is highly conserved. By electron microscopy, anti-PM-Scl antibodies reacted primarily with the granular component of the nuc1eolus. Drugs that inhibit rRNA synthesis had a marked effect on the expression of PM-Scl antigen. In actinomycin D-treated cells, immunofluorescence staining by anti-PM-Scl was signüicantly reduced with residual staining restricted to the granular regions of nuc1eoli. Treatment with 5,6-dichloro-beta-D- ribofuranosylbenzimidazole (DRB) also selectively reduced nuc1eolar staining. On a molecular level, anti-PM-Sel antibodies precipitated 11 polypeptides with molecular weights (Mr) ranging from 110,000 to 20,000. The Mr 80,000 and 20.000 polypeptides were phosphorylated. Evidence suggests that the PM-Scl antigen complex may be related to a prerlbosomal particle. Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33191 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Das Chromatin : seine Struktur und Funktion N2 - no abstract available KW - Chromatin Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-80790 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Harold Garnet Callan 1917-1993 N2 - Professor Harold Gamet Callan, honorary member of the German Society for Cell Biology, died on the 3rd November 1993, at the age of 76. His name is inseparably connected with lampbrush chromosomes, the most spectacular and aesthetically ailuring form of chromosomes, which occupied the major part of his scientific career. " Mick" Callan's pioneering studies led to fruitful new concepts, served as a building block for many subsequent studies by others, and contributed enormously to our current understanding of chromosome organization and activity ... KW - Harold Garnet Callan Y1 - 1994 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-80789 ER - TY - JOUR A1 - Fischer, D. A1 - Weisenberger, D. A1 - Scheer, Ulrich T1 - In situ hybridization of DIG-labeled rRNA probes to mouse liver ultrathin sections N2 - No abstract available. KW - Hybridisierung Y1 - 1992 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-69458 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Herth, Werner T1 - Cytologie, allgemeine und molekulare Cytologie N2 - No abstract available Y1 - 1973 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40547 ER - TY - JOUR A1 - Franke, Werner W. A1 - Zentgraf, Hanswalter A1 - Scheer, Ulrich T1 - Membrane linkages at the nuclear envelope N2 - Electron-opaque material is shown in the perinuclear cisternae of various cell types to connect the inner and outer nuclear membrane faces. Similar bridges were observed between the outer nuclear membrane and the outer mitochondrial membrane. The intracisternal bridges of the nuclear envelope appear to be important for the structural stability of the perinuclear cisterna. Stable structural linkage of mitochondria to the outer nuclear membrane might be relevant to the understanding of the characteristic juxtanuclear accumulation of mitochondria and also provide arguments for the discussions of certain biochemical activities found in nuclear and nuclear membrane fractions. KW - Cytologie Y1 - 1973 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40596 ER - TY - JOUR A1 - Spring, Herbert A1 - Trendelenbrug, Michael F. A1 - Scheer, Ulrich A1 - Franke, Werner W. A1 - Herth, Werner T1 - Structural and biochemical studies of the primary nucleus of two green algal species, Acetabularia mediterranea and Acetabularia major N2 - Primary (giant) nuclei of the green algae Acetabularia mediterranea and A. major were studied by light and electron microscopy using in situ fixed material as well as manually isolated nuclear components. In addition, cytochemical reactions of nuclear structures and biochemical determinations of nuclear and cytoplasmic RNA and of genome DNA content were performed. The data obtained and the structures observed are interpreted as demonstralions of transcriptional activities of different gene classes. The most prominent class is the nucleolar cistrons of precursors of ribosomal RNA which occur highly repeated in clusters in the form of regularly alternating intercepts on deoxyribonucleoprotein axes of transcribed rDNA, the fibril-covered matrix units, and the fibril-free "spacer" segments. A description and a classification of the various structural complexes which seem to represent transcriptional activities is given. Quantitative evaluations of these arrangements are presented. The morphology and the dimensions of such structures are compared with the RNA molecular weight determinations and with the corresponding data reported from various animal cell systems. It is suggested that the formation of the giant nucleus is correlated with, and probably due to, an enormous amplification of transcriptionally active rDNA and packing of the extrachromosomal copies into the large nucleolar aggregate bodies. KW - Cytologie KW - Nucleolus KW - electron microscopy KW - Acetabularia KW - transcription KW - gene activity KW - ribosomes Y1 - 1974 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40600 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - Some structural differentiations in the HeLa cell: heavy bodies, annulate lamellae and cotte de maillet endoplasmic reticulum N2 - A small fraction of HeLa cells within an exponentially growing culture showed cisternal differentiations, such as cytoplasmic as well as intranuclear annulate lamellae and special smooth surfaced endoplasmic reticulum aggregates with a typical "Cotte de maillet" appearance. Additionally, clusters of dense granules were observed in the cytoplasm which were often associated with polysomes and strongly resembled the so-called "heavy bodies" known in particular in diverse oocytes. The functional meaning of these structures is discussed. Moreover, it is deduced from the ultrastructural identity of the pore complexes in the nuclear envelope and the cytoplasmic and intranuclear annulate lamellae that the pore complex material with its highly ordered arrangement is not a structure characteristic for nucleocytoplasmically migrating material, but rather is a general structural expression of a tight binding of ribonucleoprotein (RNP) to cisternal membranes. The pore complexes are thought of as representing sites of a RNP-storage. A similar functioning is hypothesized for the "heavy body"like aggregates. To the current hypotheses on the formation of annulate lamellae and the nuclear envelope, which are based on the concept of membrane continuities and constancies, the alternative view of a self assembly mechanism of membrane constituents on nucleoprotein structures is added. KW - Cytologie Y1 - 1971 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40614 ER - TY - JOUR A1 - Müller, R. A1 - Scheer, Ulrich T1 - Klangspektrographische Untersuchungen der Lautäußerung beim Krallenfrosch, Xenopus laevis N2 - No abstract available Y1 - 1970 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40529 ER - TY - JOUR A1 - Weisenberger, Dieter A1 - Scheer, Ulrich A1 - Benavente, Ricardo T1 - The DNA topoisomerase I inhibitor camptothecin blocks postmitotic reformation of nucleoli in mammmalian cells N2 - No abstract available KW - Cytologie KW - Nucleolus-DNA KW - opoisomerase I KW - camptothecin KW - mitosis Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41434 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Zentgraf, Hanswalter T1 - Organization of transcriptionally active and inactive chromatin N2 - No abstract available KW - Deutschland KW - Gefäßpflanzen KW - Verzeichnis Y1 - 1984 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40588 ER - TY - CHAP A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Zentgraf, Hanswalter A1 - Trendelenburg, Michael F. A1 - Müller, U. A1 - Krohne, G. A1 - Spring, H. T1 - Organization of transcribed and nontranscribed chromatin N2 - No abstract available KW - Tumor / Zellteilung Y1 - 1980 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40656 ER - TY - JOUR A1 - Benavente, Ricardo A1 - Reimer, Georg A1 - Rose, Kathleen M. A1 - Hügle-Dörr, Barbara A1 - Scheer, Ulrich T1 - Nucleolar changes after microinjection of antibodies to RNA polymerase I into the nucleus of mammalian cells N2 - 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. Y1 - 1988 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40666 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Kleinschmidt, Jürgen A. A1 - Franke, Werner W. T1 - Transcriptional and skeletal elements in nucleoli of amphibian oocytes N2 - No abstract available Y1 - 1982 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40625 ER - TY - JOUR A1 - Eckert, W. A. A1 - Franke, Werner W. A1 - Scheer, Ulrich T1 - Actinomycin D and the central granules in the nuclear pore complex: thin sectioning versus negative staining N2 - Thin section electron microscopy of Actinomycin D treated Tetrahymena cells and amphibian oocytes (Xenopus laevis, Triturus aZpestris) reveal no reduction in the central granules in the nuclear pore complexes. Possible reasons for the diversity between these results and earlier observations using negatively stained isolated nuclear envelopes from the same objects are discussed. The results clearly show that the presence of central granules within the nuclear pores does neither depend on nuclear RNA synthesis nor does indicate nucleocytoplasmic RNA transport. This conclusion leads to a reconsideration of the nature of the central granule. The functioning of the central granule of the nuclear pore complexes is further discussed in connection with recent studies on the ultrastructure of various types of cisternal pores. KW - Nuclear pores KW - Nucleocytoplasmic exchange KW - Actinomycin D KW - Tetrahymena KW - Amphibian oocytes Y1 - 1972 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40636 ER - TY - JOUR A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Trendelenburg, Michael F. A1 - Spring, Herbert A1 - Zentgraf, Hanswalter T1 - Absence of nucleosomes in transcriptionally active chromatin N2 - 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. KW - Cytologie KW - Chromatin structure KW - nucleosomes KW - transcription KW - electron microscopy Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40646 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Franke, Werner W. T1 - Transcriptional complexes of nucleolar genes N2 - No abstract available Y1 - 1976 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41072 ER - TY - JOUR A1 - Scheer, Ulrich A1 - Messner, Karin A1 - Hazan, Rachel A1 - Raska, Ivan A1 - Hansmann, Paul A1 - Falk, Heinz A1 - Spiess, Eberhard A1 - Franke, Werner W. T1 - High sensitivity immunolocalization of double and single-stranded DNA by a monoclonal antibody N2 - 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. KW - Cytologie KW - DNA antibodies KW - monoclonal antibodies KW - DNA immunolocalization KW - chromatin KW - mycoplasma tests Y1 - 1987 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41063 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Structural organization of spacer chromatin between transcribed ribosomal RNA genes in amphibian oocytes N2 - 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. KW - Cytologie KW - Chromatin structure KW - rDNA KW - amphibian oocytes Y1 - 1980 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41057 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Entwicklung der Gametogonien in ektopisch transplantierten Gonaden bei Triturus N2 - 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. N2 - 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. Y1 - 1969 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-40510 ER - TY - CHAP A1 - Scheer, Ulrich A1 - Dabauvalle, Marie-Christine T1 - Functional organization of the amphibian oocyte nucleus N2 - No abstract available KW - Oogenese Y1 - 1985 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41178 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Injection of antibodies into the nucleus of amphibian oocytes: an experimental means of interfering with gene expression in the living cell N2 - No abstract available Y1 - 1986 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41182 ER - TY - JOUR A1 - Dabauvalle, Marie-Christine A1 - Scheer, Ulrich T1 - Assembly of nuclear pore complexes in Xenopus egg extract N2 - No abstract available Y1 - 1991 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41194 ER - TY - JOUR A1 - Hock, Robert A1 - Moormann, Antoon A1 - Fischer, Dagmar A1 - Scheer, Ulrich T1 - Absence of somatic histone H1 in oocytes and preblastula embryos of Xenopus laevis N2 - 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. Y1 - 1993 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41350 ER - TY - JOUR A1 - Kleinschmidt, Jürgen A. A1 - Scheer, Ulrich A1 - Dabauvalle, Marie-Christine A1 - Bustin, Michael A1 - Franke, Werner W. T1 - 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 N2 - No abstract available Y1 - 1983 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-33250 ER - TY - JOUR A1 - Thiry, Marc A1 - Scheer, Ulrich A1 - Goessens, Guy T1 - Localization of nucleolar chromatin by immunocytochemistry and in situ hybridization at the electron microscopic level N2 - Nucleoli are the morphological expression of the activity of a defined set of chromosomal segments bearing rRNA genes. The topological distribution and composition of the intranucleolar chromatin as well as the definition of nucleolar structures in which enzymes of the rDNA transcription machinery reside have been investigated in mammalian cells by various immunogold labelling approaches at the ultrastructural level. The precise intranucleolar location of rRNA genes has been further specified by electron microscopic in situ hybridization with a non-autoradiographic procedure. Our results indicate that the fibrillar centers are the sole nucleolar structures where rDNA, core histones, RNA polymerase I and DNA to po isomerase I are located together. Taking into account the potential value and limitations of immunoelectron microscopic techniques, we propose that transcription of the rRNA genes takes place within the confines of the fibrillar centers, probably close to the boundary regions to the surrounding dense fibrillar component. Y1 - 1991 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-39289 ER - TY - CHAP A1 - Franke, Werner W. A1 - Scheer, Ulrich A1 - Trendelenburg, Michael F. A1 - Zentgraf, H. A1 - Spring, H. T1 - Morphology of transcriptionally active chromatin N2 - 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. Y1 - 1978 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-41097 ER - TY - JOUR A1 - Scheer, Ulrich T1 - Boveri's research at the Zoological Station Naples: Rediscovery of his original microscope slides at the University of Würzburg JF - Marine Genomics N2 - Eric Davidson once wrote about Theodor Boveri: "From his own researches, and perhaps most important, his generalized interpretations, derive the paradigms that underlie modern inquiries into the genomic basis of embryogenesis" (Davidson, 1985). As luck would have it, the "primary data" of Boveri's experimental work, namely the microscope slides prepared by him and his wife Marcella during several stays at the Zoological Station in Naples (1901/02, 1911/12 and 1914), have survived at the University of Wurzburg. More than 600 slides exist and despite their age they are in a surprisingly good condition. The slides are labelled and dated in Boveri's handwriting and thus can be assigned to his published experimental work on sea urchin development. The results allowed Boveri to unravel the role of the cell nucleus and its chromosomes in development and inheritance. Here, I present an overview of the slides in the context of Boveri's work along with photographic images of selected specimens taken from the original slides. It is planned to examine the slides in more detail, take high-resolution focal image series of significant specimens and make them online available. KW - Sea urchin development KW - Polyspermy KW - Multipolar mitosis KW - Aneuploidy KW - Merogone experiments KW - Science history Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-228453 VL - 40 ER -