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.

Behaviour of nucleolus organizing regions (NORs) and nucleoli during mitotic and meiotic divisions in budding yeast.

Abstract: Spatial organization and segregation behaviour in mitosis and meiosis of nucleoli and NORs of Saccharomyces cerevisiae were examined by fluorescence in situ hybridization (FISH) and immunostaining, and integrated with previous ultrastructural studies Our observations suggest that in interphase the NOR-bearing chromosome arm forms a hairpin-shaped loop inside the nucleolus, unlike the other arms which adopt a Rabl-like orientation Prior to mitosis and meiosis, the appearance of the NOR changes from puffed to thread-shaped In mitosis, it is stretched between the mother and daughter nuclei and seems to be among the last regions where chromatids separate The nucleoli remain intact and split at the end of anaphase Similarly, during meiosis I, intact nucleoli trail behind the separating homologous NORs and are partitioned equally to the two half-nuclei During the second meiotic division, however, the nucleolus, together with a major portion of the nucleoplasm and the nuclear pore complexes, are not included in the spores The behaviour of nucleoli in meiotic mutants and a strain with extrachromosomal rDNA suggests that they are not actively extruded but rather are lost due to their detachment from the separating chromosomes We discuss the possibility that the exclusion of the nucleolus from the spores serves the disposal of agents that resort to the nucleolus, and has a role in spore dormancy or rejuvenation

Organization of the double-stranded RNA-activated protein kinase DAI and virus-associated VA RNAI in adenovirus-2-infected HeLa cells

Abstract: We have examined the cellular distribution of the double-stranded RNA-activated protein kinase DAI in adenovirus 2 (Ad2)-infected and uninfected HeLa cells. In uninfected cells DAI was found to be concentrated in the cytoplasm. In addition, DAI was localized in the nucleoli and diffusely distributed throughout the nucleoplasm. Cells treated with alpha-interferon displayed a similar pattern of distribution for DAI. When RNA polymerase I activity was inhibited by the drug actinomycin D, nucleoli segregated and DAI was found to colocalize with the dense fibrillar region of the nucleoli. During mitosis, the distribution of DAI paralleled that of rRNA. In adenovirus-infected cells the localization of DAI was similar to that in uninfected interphase cells. VA RNAI was detected in Ad2-infected cells by 10-14 hours post-infection as fine dots in the nucleoplasm. By 18-24 hours post-infection, VA RNAI appeared in bigger and more abundant dots in the nucleoplasm and the cytoplasm was intensively labeled. Transient expression of the VA RNAI gene in uninfected cells resulted in a similar localization of the RNA. Our results are consistent with a role for DAI and VA RNAI in protein synthesis and suggest that DAI may play an early role in ribosome biogenesis in the nucleolus in addition to its cytoplasmic role in translation.

Structure and epigenetics of nucleoli in comparison with non-nucleolar compartments.

Abstract: The nucleolus is a nuclear compartment that plays an important role in ribosome biogenesis. Some structural features and epigenetic patterns are shared between nucleolar and non-nucleolar compartments. For example, the location of transcriptionally active mRNA on extended chromatin loop species is similar to that observed for transcriptionally active ribosomal DNA (rDNA) genes on so-called Christmas tree branches. Similarly, nucleolus organizer region-bearing chromosomes located a distance from the nucleolus extend chromatin fibers into the nucleolar compartment. Specific epigenetic events, such as histone acetylation and methylation and DNA methylation, also regulate transcription of both rRNA- and mRNA-encoding loci. Here, we review the epigenetic mechanisms and structural features that regulate transcription of ribosomal and mRNA genes. We focus on similarities in epigenetic and structural regulation of chromatin in nucleoli and the surrounding non-nucleolar region and discuss the role of proteins, such as heterochromatin protein 1, fibrillarin, nucleolin, and upstream binding factor, in rRNA synthesis and processing.