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Showing papers on "Nucleolar chromatin published in 2018"


Journal ArticleDOI
TL;DR: It is shown that establishment of H2BS14p is necessary for damage‐induced rDNA transcriptional shut down and maintenance of genomic integrity and the impact of chromatin regulation in the rDNA damage response and targeting of the nucleolus as an emerging cancer therapeutic approach.
Abstract: The heavily transcribed rDNA repeats that give rise to the ribosomal RNA are clustered in a unique chromatin structure, the nucleolus. Due to its highly repetitive nature and transcriptional activity, the nucleolus is considered a hotspot of genomic instability. Breaks in rDNA induce a transient transcriptional shut down to conserve energy and promote rDNA repair; however, how nucleolar chromatin is modified and impacts on rDNA repair is unknown. Here, we uncover that phosphorylation of serine 14 on histone H2B marks transcriptionally inactive nucleolar chromatin in response to DNA damage. We identified that the MST2 kinase localises at the nucleoli and targets phosphorylation of H2BS14p in an ATM‐dependent manner. We show that establishment of H2BS14p is necessary for damage‐induced rDNA transcriptional shut down and maintenance of genomic integrity. Ablation of MST2 kinase, or upstream activators, results in defective establishment of nucleolar H2BS14p, perturbed DNA damage repair, sensitisation to rDNA damage and increased cell lethality. We highlight the impact of chromatin regulation in the rDNA damage response and targeting of the nucleolus as an emerging cancer therapeutic approach.

27 citations


Posted ContentDOI
30 Jul 2018-bioRxiv
TL;DR: Investigation of mitotic chromosome instability using the budding yeast, Saccharomyces cerevisiae, as a model system shows that chromosomes are indeed lost during aging of these cells due to the depletion of several key proteins that function in organizing and maintaining chromosome architecture, including the cohesin complex.
Abstract: Sir2 is a highly conserved NAD+-dependent histone deacetylase that functions in heterochromatin formation and promotes replicative lifespan (RLS) in the budding yeast, Saccharomyces cerevisiae. Within the yeast rDNA locus, Sir2 is required for efficient cohesin recruitment and maintaining stability of the tandem array. In addition to the rDNA, ChIP-seq of an epitope-tagged cohesin subunit (Mcd1-13xMyc) in a sir2? mutant revealed subtle reductions of cohesin binding at all 16 centromeres. Coupled with the previously reported chromosome instability in sir2? cells and depletion of Sir2 in aged cells, we hypothesized that mitotic chromosome instability (CIN) due to Sir2 depletion could be a driver of replicative aging. In addition to Sir2, we discovered that other subunits of the Sir2-containing SIR and RENT complexes were depleted in aged cells, as were subunits of the cohesin and monopolin/cohibin complexes, implying the possibility of CIN. ChIP assays of the residual Mcd1-13xMyc in aged cells showed strong depletion from the rDNA and possible redistribution to centromeres, most likely in an attempt to maintain chromosome stability. Despite the shift in cohesin distribution, sister chromatid cohesion was partially attenuated in old cells and the frequency of chromosome loss was increased. This age-induced CIN was exacerbated in strains lacking Sir2 and its paralog, Hst1, but suppressed in strains that stabilize the rDNA array due to the deletion of FOB1 or through caloric restriction (CR). Furthermore, ectopic expression of MCD1 from a doxycycline-inducible promoter was sufficient to suppress to rDNA instability in aged cells and to extend RLS. Taken together we conclude that age-induced depletion of cohesin and multiple other nucleolar chromatin factors destabilize the rDNA locus, which then results in general CIN and aneuploidy that shortens RLS.

1 citations


Posted ContentDOI
18 May 2018-bioRxiv
TL;DR: H4G nucleolar localization increased rRNA levels, protein synthesis rates, and cell cycle progression, and micrococcal nuclease digestion of H4G-containing nucleosomes reconstituted in vitro indicated that H 4G destabilizes the nucleosome, which may serve to alter nucleolar chromatin in a way that enhances rDNA transcription in breast cancer tissues.
Abstract: Histone variants, present in various cell types and tissues, are known to exhibit different functions. For example, histone H3.3 and H2A.Z are both involved in gene expression regulation, whereas H2A.X is a specific variant that responds to DNA double-strand breaks. In this study, we characterized H4G, a novel hominidae-specific histone H4 variant. H4G expression was found in a variety of cell lines and was particularly overexpressed in the tissues of breast cancer patients. H4G was found to localize primarily to the nucleoli of the cell nucleus. This localization was controlled by the interaction of the alpha helix 3 of the histone fold motif with the histone chaperone, nucleophosphomin 1. In addition, we found that H4G nucleolar localization increased rRNA levels, protein synthesis rates, and cell cycle progression. Furthermore, micrococcal nuclease digestion of H4G-containing nucleosomes reconstituted in vitro indicated that H4G destabilizes the nucleosome, which may serve to alter nucleolar chromatin in a way that enhances rDNA transcription in breast cancer tissues.

1 citations