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.

WRN helicase accelerates the transcription of ribosomal RNA as a component of an RNA polymerase I-associated complex.

Abstract: Werner syndrome (WS) is a rare autosmomal recessive genetic disorder causing premature aging. The gene (WRN) responsible for WS encodes a protein homologous to the RecQ-type helicase. WRN has a nucleolar localization signal and shows intranuclear trafficking between the nucleolus and the nucleoplasm. WRN is recruited into the nucleolus when rRNA transcription is reactivated in quiescent cells. Inhibition of mRNA transcription with α-amanitin has no effect on nucleolar localization of WRN whereas inhibition of rRNA transcription with actinomycin D releases WRN from nucleoli, suggesting that nucleolar WRN is closely related to rRNA transcription by RNA polymerase I (RPI). A possible function of WRN on rRNA transcription through interaction with RPI is supported by the results described here showing that WRN is co-immunoprecipitated with an RPI subunit, RPA40. Here we show that WS fibroblasts are characterized by a decreased level of rRNA transcription compared with wild-type cells, and that the decreased level of rRNA transcription in WS fibroblasts recovers when wild-type WRN is exogenously expressed. By contrast, exogenously expressed mutant-type WRN lacking an ability to migrate into the nucleolus fails to stimulate rRNA transcription. These results suggest that WRN promotes rRNA transcription as a component of an RPI-associated complex in the nucleolus.

The nucleolus: a central response hub for the stressors that drive cancer progression

Abstract: The nucleolus is a sub-nuclear body known primarily for its role in ribosome biogenesis. Increased number and/or size of nucleoli have historically been used by pathologists as a prognostic indicator of cancerous lesions. This increase in nucleolar number and/or size is classically attributed to the increased need for protein synthesis in cancer cells. However, evidences suggest that the nucleolus plays critical roles in many cellular functions in both normal cell biology and disease pathologies, including cancer. As new functions of the nucleolus are elucidated, there is mounting evidence to support the role of the nucleolus in regulating additional cellular functions, particularly response to cellular stressors, maintenance of genome stability, and DNA damage repair, as well as the regulation of gene expression and biogenesis of several ribonucleoproteins. This review highlights the central role of the nucleolus in carcinogenesis and cancer progression and discusses how cancer cells may become “addicted” to nucleolar functions.

Requirement of fission yeast Cid14 in polyadenylation of rRNAs.

Abstract: Polyadenylation in eukaryotes is conventionally associated with increased nuclear export, translation, and stability of mRNAs In contrast, recent studies suggest that the Trf4 and Trf5 proteins, members of a widespread family of noncanonical poly(A) polymerases, share an essential function in Saccharomyces cerevisiae that involves polyadenylation of nuclear RNAs as part of a pathway of exosome-mediated RNA turnover Substrates for this pathway include aberrantly modified tRNAs and precursors of snoRNAs and rRNAs Here we show that Cid14 is a Trf4/5 functional homolog in the distantly related fission yeast Schizosaccharomyces pombe Unlike trf4 trf5 double mutants, cells lacking Cid14 are viable, though they suffer an increased frequency of chromosome missegregation The Cid14 protein is constitutively nucleolar and is required for normal nucleolar structure A minor population of polyadenylated rRNAs was identified These RNAs accumulated in an exosome mutant, and their presence was largely dependent on Cid14, in line with a role for Cid14 in rRNA degradation Surprisingly, both fully processed 25S rRNA and rRNA processing intermediates appear to be channeled into this pathway Our data suggest that additional substrates may include the mRNAs of genes involved in meiotic regulation Polyadenylation-assisted nuclear RNA turnover is therefore likely to be a common eukaryotic mechanism affecting diverse biological processes