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: This review addresses the problem of understanding nucleolar morphology in terms of nucleolar function by reviewing in situ-cytochemical results that have not led to a generally accepted view on the structure-function correlation for nucleoli.
138 citations
TL;DR: Findings show that rRNA genes are a mosaic of canonical and (presumably nonfunctional) palindromic units that may be altered by factors associated with genomic instability and pathology.
Abstract: The standard model of eukaryotic ribosomal RNA (rRNA) genes involves tandem arrays with hundreds of units in clusters, the nucleolus organizer regions (NORs). A first genomic overview for human cells is reported here for these regions, which have never been sequenced in their totality, by using molecular combing. The rRNA-coding regions are examined by fluorescence on single molecules of DNA with two specific probes that cover their entire length. The standard organization assumed for rDNA units is a transcribed region followed by a nontranscribed spacer. While we confirmed this arrangement in many cases, unorthodox patterns were also observed in normal individuals, with one-third of the rDNA units rearranged to form apparently palindromic structures (noncanonical units) independent of the age of the donors. In cells from individuals with a deficiency in the WRN RecQ helicase (Werner syndrome), the proportion of palindromes increased to one-half. These findings, supported by Southern blot analyses, show that rRNA genes are a mosaic of canonical and (presumably nonfunctional) palindromic units that may be altered by factors associated with genomic instability and pathology.
138 citations
TL;DR: Homologs for both snoRNA-associated protein pairs occur in Archaea, strengthening the hypothesis that the box C/D RNA elements and their interacting proteins are of ancient evolutionary origin.
Abstract: The eukaryotic nucleolus contains a diverse population of small nucleolar RNAs (snoRNAs) essential for ribosome biogenesis. The box C/D snoRNA family possesses conserved nucleotide boxes C and D that are multifunctional elements required for snoRNA processing, snoRNA transport to the nucleolus, and 2'-O-methylation of ribosomal RNA. We have previously demonstrated that the assembly of an snoRNP complex is essential for processing the intronic box C/D snoRNAs and that specific nuclear proteins associate with the box C/D core motif in vitro. Using a box C/D motif derived from mouse U14 snoRNA, we have now affinity purified and defined four mouse proteins that associate with this minimal RNA substrate. These four proteins consist of two protein pairs: members of each pair are highly related in sequence. One protein pair corresponds to the essential yeast nucleolar proteins Nop56p and Nop58p. Affinity purification of mouse Nop58 confirms observations made in yeast that Nop58 is a core protein of the box C/D snoRNP complex. Isolation of Nop56 using this RNA motif defines an additional snoRNP core protein. The second pair of mouse proteins, designated p50 and p55, are also highly conserved among eukaryotes. Antibody probing of nuclear fractions revealed a predominance of p55 and p50 in the nucleoplasm, suggesting a possible role for the p50/p55 pair in snoRNA production and/or nucleolar transport. The reported interaction of p55 with TATA-binding protein (TBP) and replication A protein as well as the DNA helicase activity of p55 and p50 may suggest the coordination of snoRNA processing and snoRNP assembly with replication and/or transcriptional events in the nucleus. Homologs for both snoRNA-associated protein pairs occur in Archaea, strengthening the hypothesis that the box C/D RNA elements and their interacting proteins are of ancient evolutionary origin.
137 citations
TL;DR: Application of this technique to other mammalian species strongly indicated that the N-band-positive sites coincide with nucleolus organisers, and in rat kangaroo chromosomes, the N bands appeared exclusively in the nucleolu organisers.
Abstract: THE in situ DNA-RNA hybridisation techniques to locate a certain genome fraction with unique nucleotide sequences1–6 have assigned ribosomal cistrons to the satellites of human D and G group chromosomes4,5. This is of particular interest because the satellites organise nucleoli in somatic7 and meiotic cells8–10. During the course of study on the Giemsa banding mechanism (unpublished) we found that the satellite bodies of human acrocentrics can be differentially stained with Giemsa after simple procedures including extraction of both nucleic acids and histones. The staining profile, herein referred to as ‘N band’, differed clearly from the Quinacrine, Giemsa, Reversed-Giemsa, Centromeric, or Giemsa 11 banding patterns11,12. In rat kangaroo chromosomes, the N bands appeared exclusively in the nucleolus organisers13,14, that is, in the secondary constriction of the X chromosome. Further application of this technique to other mammalian species strongly indicated that the N-band-positive sites coincide with nucleolus organisers.
137 citations
TL;DR: The fact that dysregulation of many of these fundamental cellular processes may contribute to the malignant phenotype suggests that normal functioning of the nucleolus safeguards against the development of cancer and indicates its potential as a therapeutic approach.
137 citations