An electron microscopic study of nucleolus‐organizing regions at some stages of the cell cycle (G0 period, G2 period, mitosis)

Hozák, Pavel; Зацепина, О. В.; Vasilyeva, I. E.; Chentsov, Yu. S.

doi:10.1111/j.1768-322x.1986.tb00476.x

Cited by 35 publications

(24 citation statements)

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“…Intranucleolar chromatin has been suggested to loosen out from the nucleolar-organizing region (NOR) and form a complicated network in Zea mays and Sinapis alba (Motte et al 1991). The nucleolonema has also been recorded in some mammalian cells (Locke and Leung 1985;Hozak et al 1986). Unfortunately, it has not yet been accepted as an essential entity of the nucleolus.…”

Section: Introductionmentioning

confidence: 97%

Nucleolonema as a fundamental substructure of the nucleolus

et al. 2005

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The nucleolus is the most obvious structure in the eukaryotic nucleus. It is known to be a ribosome-producing apparatus where ribosomal (r) DNA is transcribed and the primary rRNA transcripts are processed to produce three of the four rRNA species. Electron microscopy has shown that the nucleolus consists of three major components, a dense fibrillar component (DFC), a granular component (GC) and a fibrillar center (FC). The DFC and FCs are integrated into a fundamental nucleolar substructure called the nucleolonema. The DFC corresponds to the matrix of the nucleolonema, and the FC is an electron microscopic counterpart of argyrophobic lacunae localized in the nucleolonema. The spherical FCs are intermittently arranged along the length of the nucleolonema in actively growing cells but are fused with each other to form tubular FCs when rDNA transcription is hampered. The RNase-gold complex does not bind to the FC but to the DFC and the GC, suggesting that rDNA transcription does not occur in the FC although both fluorescence in situ hybridization (FISH) and electron microscopic in situ hybridization reveal that the rDNA is specifically localized in the FCs. Immunogold-labeling after bromo-UTP (BrUTP) incorporation shows that rDNA transcription takes place in the boundary region between the FC and the DFC, and primary rRNA transcripts are expected to be processed outward within the DFC. Data have accumulated suggesting that the nucleolonema is a fundamental substructure of the nucleolus, and its skeleton is the tandem arrangement of the FCs, which are resting harbors or storages of rDNA. This paper proposes that the transversal structural organization of the nucleolonema is centrifugally built up by several structural and functional domains: condensed and/or loosened rDNA, rDNA transcription zone, and transcript processing and ribosome assembly zones.

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Section: Introductionmentioning

confidence: 97%

Nucleolonema as a fundamental substructure of the nucleolus

et al. 2005

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“…Dynamic changes to patterns of chromatin condensation are associated with altered cell activity and the cell cycle. Within the nucleolus, increased rDNA transcription is associated with an altered distribution of rDNA heterochromatin (142) as well as changing size and number of nucleoli (86) and nucleolus ultrastructure (78). Phytohemagglutinin stimulation of mammalian lymphocytes promotes the cell into the cell cycle from G 0 and causes the decondensation of chromatin and changing ultrastructure of the nucleolus, particularly a decrease in size and an increase in the number of fibrillar centers (50,79,81).…”

Section: Dynamic Changes To Interphase Nuclei In Cycling Cellsmentioning

confidence: 99%

Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells

Leitch

2000

Microbiol Mol Biol Rev

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SUMMARY The review examines the structured organization of interphase nuclei using a range of examples from the plants, animals, and fungi. Nuclear organization is shown to be an important phenomenon in cell differentiation and development. The review commences by examining nuclei in dividing cells and shows that the organization patterns can be dynamic within the time frame of the cell cycle. When cells stop dividing, derived differentiated cells often show quite different nuclear organizations. The developmental fate of nuclei is divided into three categories. (i) The first includes nuclei that undergo one of several forms of polyploidy and can themselves change in structure during the course of development. Possible function roles of polyploidy is given. (ii) The second is nuclear reorganization without polyploidy, where nuclei reorganize their structure to form novel arrangements of proteins and chromosomes. (iii) The third is nuclear disintegration linked to programmed cell death. The role of the nucleus in this process is described. The review demonstrates that recent methods to probe nuclei for nucleic acids and proteins, as well as to examine their intranuclear distribution in vivo, has revealed much about nuclear structure. It is clear that nuclear organization can influence or be influenced by cell activity and development. However, the full functional role of many of the observed phenomena has still to be fully realized.

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“…In this paper we compared the distribution of UBF and rDNA during the cell cycle in cultured pig embryonic kidney (PK) cells using both conventional and confocal laser scanning microscopy. PK cells were studied because of their low and usually constant number of NORs (four per diploid set of chro mosomes; Hozak et al, 1986;Zatsepina et al, 1988). The total number of chromosomes (38-40 in 80% of metaphase cells) was found to be close to that in the wild pig karyotype (2n = 38), with all NORs being located near the centromeres (Czaker and Mayr.…”

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The RNA polymerase I transcription factor UBF and rDNA are located at the same major sites in both interphase and mitotic pig embryonic kidney (PK) cells

Зацепина¹,

Schöfer²,

Weipoltshammer³

et al. 1996

Cytogenet Genome Res

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Indirect immunolabeling with anti-UBF antibodies, in situ hybridization with an rDNA probe, and confocal scanning laser microscopy were used to study nucleolar organizer regions (NORs) during the cell cycle in pig embryonic kidney (PK) cells. The chromosomal distribution of the polymerase I transcription factor UBF and rDNA was compared with the number of silver-stained NORs (Ag-NORs) present and nucleolar size. It was shown, both at interphase and mitosis, that the majority of UBF and rDNA signals were located at the same foci and that the amounts of UBF and rDNA at any given site were in a striking positive correlation. At mitosis, only the NORs were labeled; at interphase, the signals for both UBF and rDNA were arranged in necklace-like structures around the nucleoli. No chromosomal NORs without Ag-proteins or UBF were present, indicating that all NORs in PK cells are active at interphase. It was concluded that (1) UBF and rDNA co-localize throughout the cell cycle in PK cells; (2) their association with mitotic NORs is determined by the number of rDNA repeats, rather than by any differential ability of NORs to recruit the transcription factor; and (3) the amount of UBF can be correlated with the size and activity of the nucleoli at interphase.

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An electron microscopic study of nucleolus‐organizing regions at some stages of the cell cycle (G0 period, G2 period, mitosis)

Cited by 35 publications

References 0 publications

Nucleolonema as a fundamental substructure of the nucleolus

Nucleolonema as a fundamental substructure of the nucleolus

Higher Levels of Organization in the Interphase Nucleus of Cycling and Differentiated Cells

The RNA polymerase I transcription factor UBF and rDNA are located at the same major sites in both interphase and mitotic pig embryonic kidney (PK) cells

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