Refine
Has Fulltext
- yes (133)
Is part of the Bibliography
- yes (133)
Year of publication
Document Type
- Journal article (107)
- Conference Proceeding (12)
- Book article / Book chapter (8)
- Review (5)
- Book (1)
Keywords
- Cytologie (13)
- Amphibian oocytes (3)
- Electron microscopy (3)
- electron microscopy (3)
- mitosis (3)
- Botanik (2)
- Chromatin structure (2)
- DNA (2)
- DNA antibodies (2)
- Lampbrush chromosomes (2)
- Nucleolus (2)
- nucleolus (2)
- transcription (2)
- Acetabularia (1)
- Actinomycin D (1)
- Anatomie (1)
- Aneuploidy (1)
- Chemical nature (1)
- Chromatin (1)
- Cross-bridges (1)
- DNA immunolocalization (1)
- Deutschland (1)
- Eukaryonten / Chromosom (1)
- Gefäßpflanzen (1)
- Golgi apparatus (1)
- Harold Garnet Callan (1)
- Hybridisierung <Biologie> (1)
- Membranes (1)
- Merogone experiments (1)
- Microtubules (1)
- Multipolar mitosis (1)
- Nuclear envelope (1)
- Nuclear pore complex (1)
- Nuclear pores (1)
- Nucleocytoplasmic exchange (1)
- Nucleocytoplasmic transport (1)
- Nucleolus-DNA (1)
- Oogenese (1)
- Polyspermy (1)
- Science history (1)
- Sea urchin development (1)
- Tetrahymena (1)
- Tierpsychologie (1)
- Transcription units (1)
- Tumor / Zellteilung (1)
- Verzeichnis (1)
- Xenopus oocytes (1)
- Zelldifferenzierung (1)
- Zellkern (1)
- amphibian oocytes (1)
- anti-RNA polymerase I antibodies (1)
- antibody (1)
- cAMP / cGMP / cytoskeleton / phosphorylation / protein kinase (1)
- camptothecin (1)
- chromatin (1)
- chromatin structure (1)
- evolution (1)
- fibrillar centers (1)
- gene activity (1)
- immunofluorescence (1)
- immunofluorescence microscopy (1)
- in situ hybridization (1)
- lampbrush chromosomes (1)
- monoclonal antibodies (1)
- monoclonal antibody (1)
- mycoplasma tests (1)
- nuclear envelope (1)
- nuclear organization (1)
- nucleologenesis (1)
- nucleolus organizer (1)
- nucleosomes (1)
- opoisomerase I (1)
- rDNA (1)
- rRNA genes (1)
- ribosomal RNA genes; electron microscopy; spread preparations (1)
- ribosomes (1)
- sperm (1)
- transcription units (1)
Institute
- Theodor-Boveri-Institut für Biowissenschaften (133) (remove)
No abstract available
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.
No abstract available
The arrangement of transcriptional units in the loops of lampbrush chromosomes from oocyte nuclei of urodele amphibia and from primary nuclei of the green alga Acetabularia have been studied in the electron microscope using spread preparations. Loops with different patterns of arrangement of matrix units (i.e. to a first approximation, transcriptional units) can be distinguished: (i) loops consisting of one active transcriptional unit; (ii) loops containing one active transcriptional unit plus additional fibril-free, i.e. apparently untranscribed, intercepts that may include 'spacer' regions; (iii) loops containing two or more transcriptional units arranged in identical or changing polarities, with or without interspersed apparent spacer regions. Morphological details of the transcriptional complexes are described. The observations are not compatible with the concept that one loop reflects one and only one transcriptional unit but, rather, lead to a classification of loop types according to the arrangement of their transcriptional units. We propose that the lampbrush chromosome loop can represent a unit for the coordinate transcription of either one gene or a set of several (different) genes.
The morphology of nucleolar and non-nucleolar (Iampbrush chromosome loops) chromatin was studied in the electron microscope during states of reduced transcriptional activity in amphibian oocytes (Xenopus laevis, Triturus alpestris, T. cristatus). Reduced transcriptional activity was observed in maturing stages of oocyte development and after treatment with an inhibitor, actinomycin D. Strands of nucleolar chromatin appear smooth and thin, and contain only few, if any, nucleosomal particles in the transcribed units. This is true whether they are densely or only sparsely covered with lateral ribonucleoprotein fibrils. This smooth and non-nucleosomal character is also predominant in the interspersed, apparently nontranscribed rDNA spacer regions. During inactivation, however, nucleolar chromatin frequently and progressively assumes a beaded appearance in extended fibril-free-that is, apparently nontranscribed - regions. I n either fUll-grown 00- cytes or late after drug treatment, most of the nucleolar chromatin is no longer smooth and thin, but rather shows a beaded configuration indistinguishable from inactive non - nucleolar chromatin. In many chromatin strands, transitions of fibril-associated regions of smooth character into beaded regions wihout lateral fibrils are seen. Similarly, in the non-nucleolar chromatin of the retracting lampbrush chromosome loops, reduced transcriptional activity is correlated with a change from smooth to beaded morphology. Here, however, beaded regions are also commonly found interspersed between the more or less distant bases of the lateral fibrils, the putative transcriptional complexes. I n both sorts of chromatin, detergents (in particular Sarkosyl) that remove most of the chromatin proteins including histones from the DNA axis but leave the RNA polymerases of the transcriptional complexes attached were used to discriminate between polymerases and nucleosomal particles. The results suggest that nucleosomes are absent in heavily transcribed chromatin regions but are reformed after inactivation. In contrast to the findings with inactivated nucleolar genes, in lampbrush chromosome loops the beaded nucleosomal configuration appears to be assumed also in regions within transcriptional units that, perhaps temporarily, are not involved in transcription.
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.