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.

The herpes simplex virus 1 UL11 proteins are associated with cytoplasmic and nuclear membranes and with nuclear bodies of infected cells.

Abstract: Earlier studies have shown that the UL11 gene of herpes simplex virus encodes a myristylated virion protein and that the UL11 gene enables efficient virion envelopment and export from infected cells. A rabbit polyclonal antibody directed against an affinity-purified UL11-glutathione-S-transferase fusion protein was made and used to study the properties of the UL11 protein and its distribution in infected cells. We report the following: (i) UL11 protein formed up to five bands (apparent M(r)s, 17,000 to 22,000) in denaturing polyacrylamide gels; (ii) fluorescent-antibody studies revealed the presence of UL11 protein in the perinuclear space and in sites within the nucleus; (iii) immune electron microscopic studies indicated that the UL11 gene products were associated with the inner nuclear membrane, with cytoplasmic membranes and ribbon-like cytoplasmic structures resembling membranous organelles, with nuclear bodies shown by fluorescence microscopy to be different from nucleoli in which US11 protein accumulates, and with enveloped virions but not with nuclear capsids; and (iv) the nuclear bodies containing UL11 protein were reminiscent both of type IV morphotypes consisting of an electron-dense core containing the UL11 proteins surrounded by a more electron-transluscent core and of type V morphotypes consisting of material homogenous in electron opacity. We conclude that (i) the UL11 protein is processed after synthesis; (ii) the localization of UL11 protein with virions and membranes is consistent with the hypothesis that UL11 plays a role in the transport of virions to the extracellular space; and (iii) although the significance of the association of UL11 proteins with nuclear bodies is unknown, the results indicate that nuclear bodies differ with respect to their morphologies and contents of viral protein and suggest that UL11 protein may have more than one function in the infected cell.

Nucleolin from Xenopus laevis: cDNA cloning and expression during development.

Abstract: Nucleolin is a key nucleolar protein in higher eukaryotic cells and is involved directly in ribosome biogenesis. Using an antiserum raised against hamster nucleolin, the homologous protein was detected in nucleoli of Xenopus laevis hepatocytes as well as in the amplified nucleoli of oocytes. A cDNA encoding Xenopus nucleolin has been isolated and sequenced. The deduced protein sequence reveals similar domains in Xenopus and in mammals, but they have undergone separate evolutions. In particular, each of the four RNA-binding domains has evolved differently--the carboxy-proximal domain is twice as conserved (87%) as the amino-proximal domain (42%). These data shed some light on the possible roles of each domain. The expression of nucleolin has been followed throughout oogenesis and embryogenesis. The appearance of nucleolin during early development precedes the transcription of rDNA and the synthesis of ribosomal proteins. The maximal accumulation of nucleolin at gastrulation coincides with nucleolar reformation. Furthermore, when ribosomal synthesis is activated during oogenesis and embryogenesis, peptides immunorelated to nucleolin appear and accumulate. The results suggest that nucleolin plays a role not only in ribosome assembly but also in nucleologenesis.

Nucleolus association of chromosomal domains is largely maintained in cellular senescence despite massive nuclear reorganisation

Abstract: Mammalian chromosomes are organized in structural and functional domains of 0.1-10 Mb, which are characterized by high self-association frequencies in the nuclear space and different contact probabilities with nuclear sub-compartments. They exhibit distinct chromatin modification patterns, gene expression levels and replication timing. Recently, nucleolus-associated chromosomal domains (NADs) have been discovered, yet their precise genomic organization and dynamics are still largely unknown. Here, we use nucleolus genomics and single-cell experiments to address these questions in human embryonic fibroblasts during replicative senescence. Genome-wide mapping reveals 1,646 NADs in proliferating cells, which cover about 38% of the annotated human genome. They are mainly heterochromatic and correlate with late replicating loci. Using Hi-C data analysis, we show that interactions of NADs dominate interphase chromosome contacts in the 10-50 Mb distance range. Interestingly, only minute changes in nucleolar association are observed upon senescence. These spatial rearrangements in subdomains smaller than 100 kb are accompanied with local transcriptional changes. In contrast, large centromeric and pericentromeric satellite repeat clusters extensively dissociate from nucleoli in senescent cells. Accordingly, H3K9me3-marked heterochromatin gets remodelled at the perinucleolar space as revealed by immunofluorescence analyses. Collectively, this study identifies connections between the nucleolus, 3D genome structure, and cellular aging at the level of interphase chromosome organization.

The nucleolus in primary spermatocytes of Drosophila hydei.

Abstract: Transcribing ribosomal RNA genes in primary spermatocyte nucleoli of Drosophila hydei have been visualized by electron microscopy using a microspreading technique. The length of the transcribing unit is in agreement with the length of the ribosomal RNA precursor as determined by acrylamide gel electrophoresis (2.6×106 daltons). The length of the non-transcribed spacer is approximately 1.0×106 daltons. The maximum number of active cistrons in wild type (XY) males only approaches one half the estimated number of ribosomal cistrons of the replicated diploid genome (∼300) of D. hydei and is found to vary between 120 and 320 cistrons in different developmental stages of spermatocytes. There is also some variation between different males. In a few cases a variation in the transcriptional activity of different cistrons has been observed. The synthesis of ribosomal RNA therefore seems to be regulated primarily by the activation or inaetivation of varying numbers of ribosomal cistrons. Groups of adjacent cistrons seem to be under coordinated control. Inhibition of RNA synthesis by actinomycin, in contrast, follows a random pattern. The frequent observation of a bipartite nucleolus indicates that the nucleolus organizer regions of the two sex chromosomes are both active in transcription. The number of active ribosomal eistrons found in some X-Y translocation stocks and in XO males deviates considerably from that expected on the basis of DNA/RNA hybridization data. We conclude that, in agreement with the observations of other authors, a mechanism adjusting the number of ribosomal cistrons may be operating in these cases.