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Journal ArticleDOI

Active ribosomal cistrons and their primary transcripts located in the nucleolus

01 Mar 1987-Cell Biology International Reports (No longer published by Elsevier)-Vol. 11, Iss: 3, pp 205-210
TL;DR: The active ribosomal cistrons together with their primary transcripts and the associated proteins and enzymes forming the typical 'christmas tree' configuration in the dense nucleolar components can correlate the structural and functional organization of the nucleolus.
About: This article is published in Cell Biology International Reports.The article was published on 1987-03-01. It has received 12 citations till now. The article focuses on the topics: Ribosomal DNA & Nucleolus.
Citations
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Journal ArticleDOI
TL;DR: The three-dimensional (3D) organization of rDNA-containing chromatin was studied in structurally well preserved, interphase nuclei of Pisum sativum root tips by in situ hybridization using a biotinylated cDNA probe to the 18, 5.8 and 25 S rDNA sequences.
Abstract: The three-dimensional (3D) organization of rDNA-containing chromatin was studied in structurally well preserved, interphase nuclei ofPisum sativum root tips by in situ hybridization using a biotinylated cDNA probe to the 18, 5.8 and 25 S rDNA sequences. The probe was detected by immunofluorescence and optical section images recorded either by video imaging or by using a confocal laser scanning microscope. Detailed 3D reconstructions were made of 12 nucleoli by projection of confocal optical sections. The probe labelled four perinucleolar heterochromatin sites, one pair 1.0–2.1 µm in diameter and the other 0.5–1.0 µm diameter. It also labelled intranucleolar structures including 300–500 nm spots emanating from the perinucleolar sites into the body of the nucleolus. The intranucleolar labelled structures emanating from the perinucleolar sites lay in discrete domains. Medium power observations of 22 fields of cells (6–30 cells per field) were made by optical sectioning using a video camera and computer deblurring. The arrangement of the perinucleolar sites was modelled in each cell and the arrangements examined for nonrandomness. The sites tended to be spaced out around the nucleolar periphery approximating a regular tetrahedral arrangement as if to minimize clustering and the large sites appeared to lie in a plane perpendicular to the root axis. Cells with multiple nucleoli did not have any preferred distribution of sites between nucleoli. These observations are discussed in terms of current models of rDNA organization.

64 citations

Journal ArticleDOI
01 Jan 1994-Micron
TL;DR: The most relevant data currently available on the in situ localization of nucleolar chromatin on plant cells points towards models of similar functional organization in both plant and animal nucleoli.

41 citations

Journal ArticleDOI
TL;DR: The present observations suggest that the nucleolar dense fibrillar component, shown previously in ultrathin sections of [3H]uridine-labelled intact cells as carrying rapidly labelled pre-rRNA, in fact consists of highly compacted transcribing ribosomal genes.
Abstract: The fine structure of the nuclear components was studied following mild lysis of mouse or Drosophila tissue culture cells and spreading of nuclear material. Particular attention was paid to nuclear ribonucleoprotein (RNP) constituents, which were analysed by high resolution autoradiography after [3H]uridine pulse labelling of cells. Comparison with the labelling kinetics of various in situ nuclear RNP constituents described previously suggests strong similarities between in situ constituents and structures observed within spread nuclear components. The present observations suggest that the nucleolar dense fibrillar component, shown previously in ultrathin sections of [3H]uridine-labelled intact cells as carrying rapidly labelled pre-rRNA, in fact consists of highly compacted transcribing ribosomal genes. The growing RNP fibrils appearing in transcription complexes of extranucleolar active genes and the in situ observed perichromatin fibrils also show the same labelling properties. This confirms that the two structures indeed represent the same nucleoplasmic constituents. As for the nuclear structures involved in post-transcriptional events, our observations demonstrate the occurrence of a rapidly labelled RNP fibro-granular network. Its granular elements correspond, in size and perichromatin location, to the perichromatin granules seen in the situ preparations and suggest similarities between the two constituents. The results are discussed in the light of other data providing information on the role of various nuclear structural constituents.

16 citations

Journal ArticleDOI
TL;DR: In situ hybridization with 3H 28 S ribosomal RNA at the ultrastructural level shows labelling exclusively over the nucleolus and specifically over the dense nucleolar component (DNC).

16 citations

Journal ArticleDOI
TL;DR: Spirogyra nucleoli were shown by three-dimensional optical microscopy of DAPI fluorescence to contain DNA with a pattern and distribution matching those of the fibrillar centres, indicating this is the site of nucleolar transcription.
Abstract: Spirogyra nucleoli were shown by three-dimensional optical microscopy of DAPI fluorescence to contain DNA with a pattern and distribution matching those of the fibrillar centres. This was confirmed using different species with nucleoli showing different sizes of fibrillar centre. Much lower levels of fluorescence were seen corresponding to the dense fibrillar component. Nearly all the DAPI fluorescence arises from the fibrillar centres or from regions very close to their surface, indicating that this is the site of nucleolar transcription.

15 citations


Cites background from "Active ribosomal cistrons and their..."

  • ...The observations of what seem to be transcription units in the granular component (Ghosh and Paweletz, 1987; Hameister, 1977; Troster et al. 1985) and the axial structures with attached fibres and granules shown there by Olins and Olins (1980) in Chironomus salivary gland nucleoli warn us against too complacent an acceptance of our current views....

    [...]

References
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Journal ArticleDOI
23 May 1969-Science
TL;DR: The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules.
Abstract: The presence of extrachromosomal nucleoli in amphibian oocytes has permitted isolation and electron microscopic observation of the genes coding for ribosomal RNA precursor molecules. Visualization of these genes is possible because many precursor molecules are simultaneously synthesized on each gene. Individual genes are separated by stretches of DNA that apparently are not transcribed at the time of synthesis of precursor rRNA in the extrachromosomal nucleoli.

812 citations

BookDOI
01 Jan 1985
TL;DR: In this paper, the authors describe the structure of preribosomes and their role in the pre-rRNA precoding process, and discuss the role of RNA polymerases in the precoding.
Abstract: I. Introduction.- II. Ribosomal Genes.- II. 1. Definitions.- II.2. Ribosomal RNA Genes.- II.2.1. Multiplicity.- II.2.2. Chromosomal Location.- II.2.3. Extrachromosomal rRNA Genes.- II.2.4. Organization and Structure.- II.2.4.1. Saccharomyces cerevisiae.- II.2.4.2. Tetrahymena.- II.2.4.3. Drosophila.- II.2.4.4. Xenopus laevis.- II.2.4.5. Higher Plants.- II.2.4.6. Mammalia.- II.2.5. General Features.- II.3. 5 S rRNA Genes.- II.3.1. Number and Chromosomal Location.- II.3.2. Organization and Structure.- II.4. Ribosomal Protein Genes.- II.5. Synopsis.- III. Transcription of Ribosomal Genes.- III. 1. Components of the Transcription Complex.- III. 1.1. RNA Polymerases.- III. 1.2. Nucleolar rDNA and r-Chromatin.- III.2. The Transcription Process >.- III.2.1. Topology of Primary Pre-rRNA.- III.2.2. Morphology of Transcribed rRNA Genes.- III.2.3. Transcribed and Non-Transcribed r-Chromatin.- III.2.4. Primary Transcripts and Primary Pre-rRNA.- III.2.5. Transcription Initiation and Termination.- III.2.5.1. Initiation.- III.2.5.2. Termination.- III.2.6. Transcription in vitro.- III.3. Transcription of 5 S rRNA Genes.- III.4. Transcription of r-Protein Genes.- III.5. Synopsis.- IV. Maturation of Preribosomes.- IV. 1. Structure of Primary Pre-rRNA.- IV. 1.1. Size and Primary Structure.- IV. 1.2. Modifications.- IV. 1.3. Conformation.- IV.2. Pre-rRNA Maturation Pathways.- IV.2.1. General Considerations.- IV.2.2. Common Pattern of Pre-rRNA Maturation.- IV.2.3. Multiplicity of Maturation Pathways.- IV. 2.4. Enzyme Mechanisms.- IV. 3. Preribosomes: Structure and Maturation.- IV. 4. Synopsis.- V. Molecular Architecture of the Nucleolus.- V. 1. Introduction.- V.2. Nucleolus Organizer.- V. 2.1. Chromosomes.- V.2.2. Interphase Nuclei.- V.3. Fibrillar and Granular Components.- V.3.1. The Fibrillar Component.- V.3.2. The Granular Component.- V.4. The Nucleolus and Other Nuclear Structures.- V.4.1. Nucleolus-Associated Chromatin.- V.4.2. The Junction with the Nuclear Envelope.- V.5. The Nucleolar Matrix.- V.6. Macromolecular Constituents.- V.6.1. DNA and RNA.- V. 6.2. Nucleolar Proteins.- V.6.2.1. General.- V.6.2.2. Ag-NOR Protein(s).- V. 6.2.3. Nucleolar Antigens.- V. 7. Outline.- VI. Regulation.- VI. l. General Considerations.- VI.2. Transscriptional Control.- VI. 2.1. Transitions in the State of Expression of rRNA Genes.- VI. 2.1.1. Inactive r-Chromatin.- VI.2.1.2. Potentialy Active and Transcribed rRNA Genes.- VI.2.2. Control of Transcription Rate.- VI.2.2.1. Role of RNA Polymerase I.- VI.2.2.2. Supply of Nucleoside-5'-Triphosphates...- VI.2.2.3. Role of Protein Synthesis.- VI.3. Posttranscriptional Control.- VI.3.1. Synthesis and Supply of r-Proteins.- VI.3.2. The Role of Pre-rRNA Structure.- VI.3.3. The Role of 5 S rRNA.- VI.3.4. Critical Control Sites.- VI.3.4.1. Alternative Processing Pathways and Intranuclear Degradation of Preribosomes and Ribosomes.- VI.3.4.2. Release From the Nucleolus and Nucleo- Cytoplasmic Transport of Ribosomes.- VI.3.4.3. Turnover of Ribosomes.- VI.4. Autogeneous Regulation of Ribosome Biogenesis in Eukaryotes: A Model.- VI.5. Synopsis.- VII. Ribosome Biogenesis in the Life Cycle of Normal and Cancer Cells.- VII. 1. Nucleologenesis and Nucleololysis.- VII. 1.1. Nucleoli and Ribosome Biogenesis During the Mitotic Cycle.- VII. 1.2. Nucleologenesis.- VII. 1.3. Nuclyeololysis.- VII.2. Inhibition of Ribosome Biogenesis.- VII.2.1. Inhibitors Interacting With DNA and Chromatin.- VII.2.2. Inhibitors That Act on RNA Polymerases.- VII.2.3. Inhibitors of Nucleoside-5'-Triphosphate Formation.- VII.2.4. The Effects of Analogues Incorporated into Polyribonu- cleotide Chains.- VII.2.5. Inhibitors of Protein Synthesis.- VII.2.6. Interpretation of Nucleolar Alterations.- VII.2.6.1. Nucleolar Segregation.- VII.2.6.2. Nucleolar Spherical Bodies and Perichromatin Granules.- VII.2.6.3. Microspherules.- VII.2.6.4. Nucleolar Fragmentation.- VII.3. Growth Transitions.- VII.3.1. Modulation of Growth Rates in Yeasts.- VII.3.2. Activation of Lymphocytes.- VII.3.3. Growth Stimulation of Cultured Cells.- VII.3.4. Differentiation of Myoblasts in Culture.- VII.3.5. Regeneration of Rat Liver.- VII.4. Senescent and Cancer Cells.- VII.4.1. Senscent Cells and Tissues.- VII.4.2. Cancer Cells.- VII.5. Synopsis.- References.

514 citations

Book ChapterDOI
TL;DR: The nucleusolus is organized at the nucleolus-organizing region of the chromosomes, which are generally visible as secondary constriction regions in metaphase chromosomes, and the chromatin within the constriction region is lost at interphase inside the nucleoli.
Abstract: Publisher Summary The nucleolus is organized at the nucleolus-organizing region of the chromosomes, which are generally visible as secondary constriction regions in metaphase chromosomes. The chromatin within the constriction region is lost at interphase inside the nucleolar mass. The chromatin is highly extended at this stage. At the ultrastructural level, the nucleolus has at least three components: (1) a granular component consisting mainly of ribonucleoproteins (RNP) granules—pars granulosa, (2) a fibrillar component, consisting of RNP fibrils—pars fibrosa, and (3) chromatin elements. Chromatin elements may be present in three forms: (1) nucleolus-associated chromatin, which most likely does not take part in nucleolus formation; however, the possibility of its association with condensed inactive ribosomal cistrons, at least in some cells, cannot be overruled at present, (2) septalike intranucleolar chromatin, and (3) isolated or dispersed intranucleolar chromatin threads. Intranucleolar chromatin is often associated with the pars fibrosa. Identical components can also be found in isolated nucleoli. Studies on the nucleoli in giant chromosomes indicate that the intranucleolar chromatin in these nucleoli is present as puffs of different sizes. The nucleolar chromatin is not an autonomous structure of the nucleolus but is a continuous structure and part of the nucleolar chromosome.

372 citations

Journal ArticleDOI
TL;DR: It is concluded 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 r RNA genes during the cell cycle.
Abstract: 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 pre-rRNA, 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

295 citations

Journal ArticleDOI
TL;DR: Evidence is provided that nucleolar phosphoprotein C23 is the major silver staining protein of the nucleolus and that it is directly or indirectly associated with rDNA.

133 citations