Topic
Nucleolus
About: Nucleolus is a research topic. Over the lifetime, 5873 publications have been published within this topic receiving 232435 citations. The topic is also known as: GO:0005730 & cell nucleolus.
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TL;DR: Some recent findings describing the protein as a histone chaperone [with functional similarity to the facilitates chromatin transcription (FACT) complex] and a chromatin co-remodeler could help reconcile discrepancies in the literature regarding the role of nucleolin in transcription.
300 citations
TL;DR: In these mouse-human hybrids, unlike those that lose human chromosomes, only humanucleolus organizer activity is expressed, and mouse nucleolus organizers activity is suppressed.
Abstract: Most mouse-human somatic cell hybrids show preferential loss of human chromosomes, absence of human 28S ribosomal RNA, and suppression of human nucleolus organizer activity, as visualized by the Ag-AS silver histochemical stain. In contrast, the mouse-human hybrids studied here show preferential loss of mouse chromosomes. The hybrids were made by fusion of HT-1080-6TG human fibrosarcoma cells with BALB/c mouse peritoneal macrophages or strain 129 mouse teratocarcinoma cells. The Ag-AS staining method shows nucleolus organizer activity of chromosomes 13, 14, 15, 21 (rarely), and 22 in the human parent and chromosomes 12, 15, 16 (rarely), and 18 in the BALB/c mouse parent. In the hybrid cells the human nucleolus organizer regions are active, as shown by Ag-AS staining and involvement in "satellite association." The mouse nucleolus organizer regions are not stained by the Ag-AS method even though mouse chromosomes 12, 15, and 18 are present in the BALB/c hybrids and at least one copy of each mouse chromosome is present in the teratocarcinoma-derived hybrids. Thus, in these mouse-human hybrids, unlike those that lose human chromosomes, only human nucleolus organizer activity is expressed, and mouse nucleolus organizer activity is suppressed.
297 citations
TL;DR: It is shown that ribosomal genes are located at the outer periphery of the nucleolus in the NSN configuration and that pol I-dependent perinucleolar transcription sites correspond to specific ultrastructural features of theucleolus.
Abstract: It was previously shown that fully grown ovarian germinal vesicle (GV) oocytes of adult mice exhibit several nuclear configurations that differ essentially by the presence or absence of a ring of condensed chromatin around the nucleolus. These configurations have been termed, respectively, SN (surrounded nucleolus) and NSN (nonsurrounded nucleolus). Work from our and other laboratories has revealed ultrastructural and functional differences between these two configurations. The aims of the present study were 1) to analyze the equilibrium between the SN and the NSN population as a function of the age of the mice and the time after hCG-induced ovulation and 2) to study the polymerase I (pol I)- and polymerase II (pol II)-dependent transcription in both types of oocytes through the detection of bromouridine incorporated into nascent RNA. We show 1) that ovarian GV oocytes exhibiting the SN-type configuration can be found as soon as 17 days after birth in the C57/CBA mouse strain and 2) that the SN:NSN ratio of ovarian GV oocytes is very low just after hCG-induced ovulation and then increases progressively with the time after ovulation. Furthermore, we demonstrate that the SN configuration correlates strictly with the arrest of both pol I- and pol II-dependent transcription in mice at any age. Finally, we show that ribosomal genes are located at the outer periphery of the nucleolus in the NSN configuration and that pol I-dependent perinucleolar transcription sites correspond to specific ultrastructural features of the nucleolus. Altogether, these results provide clear-cut criteria delineating transcriptionally active GV oocytes from those that are inactive, and confirm that the SN-type configuration is mostly present in preovulatory oocytes.
296 citations
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
TL;DR: It is suggested that interactions between c- myc and Fbw7gamma within the nucleolus regulate c-Myc's growth-promoting function and that c-myc activation is likely to be an important oncogenic consequence of FbW7 loss in cancers.
291 citations