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DDX18 safeguards rDNA epigenetic landscape by counteracting PRC2 and maintains ESC identity

ABSTRACT: Here we have RNA binding protein DDX18 connecting rRNA transcription to early embryo development and embryonic stem cell (ESC) identity maintenance. DDX18 mutant embryos suffer lethality during preimplantation development. DDX18 depletion impairs ESC self-renewal and pluripotency, which phenotype-copies RNA polymerase I (RNAPI) inhibition. Mechanistically, DDX18 is recruited to rDNA by RNAPI transcription machinery and senses rRNA transcription by binding to pre-rRNA. In nucleolus, DDX18 surrounds DFC ring and interacts with PRC2. In the presence of transcribed pre-rRNA, DDX18 interaction with PRC2 makes EZH2 unstably binding to the other components of PRC2, thereby preventing PRC2 engagement and counteracting H3K27me3 mediated silencing at rDNA chromatin. Together, our study shows that DDX18 plays important roles in safeguarding ESCs identity through regulating epigenetic states of rDNA locus and maintaining euchromatin structure in nucleolus.

ORGANISM(S): Mus musculus

PROVIDER: GSE124580 | GEO | 2019/12/25

REPOSITORIES: GEO

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DDX18 safeguards rDNA epigenetic landscape by counteracting PRC2 and maintains ESC identity

Project description:DDX18 safeguards rDNA epigenetic landscape by counteracting PRC2 and maintains ESC identity

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Project description:Transcription by RNA polymerase I (RNAPI) represents most of the transcriptional activity in eukaryotic cells and is associated with the production of mature ribosomal RNA (rRNA). As several rRNA maturation steps are coupled to RNAPI transcription, the rate of RNAPI elongation directly influences processing of nascent pre-rRNA, and changes in RNAPI transcription rate can result in alternative rRNA processing pathways in response to growth conditions and stress. However, factors and mechanisms that control RNAPI progression by influencing transcription elongation rate remain poorly understood. Our project is to show that the conserved RNA-binding Seb1 is a pausing-promoting factor for RNA polymerases I to control cotranscriptional RNA processing. Here, we did a proximity dependent biotinylation followed by mass spectrometry (PDB-MS) of the Seb1 protein in order to assess for physical interactions with the RNAPI transcription machinery. A mutant E. coli BirA enzyme is fused to the Seb1 protein. This mutant version of BirA uses biotin to catalyze the formation of biotinoyl-5′-AMP (bioAMP), thereby generating a ‘cloud’ of activated biotin molecules that can react with free primary amines (most often lysine residues) of neighboring proteins. This experiment will support the conclusion that Seb1 is located at the rDNA locus.

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URB1 ensures 3' end processing of pre-rRNAs to prevent exosome-dependent degradation and is required for development [SHAPE-MaP]

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URB1 ensures 3' end processing of pre-rRNAs to prevent exosome-dependent degradation and is required for development

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FGF2 antiproliferative stimulus triggers proteomic and transcriptional changes associated with nucleolar disorganization in K-ras-driven mouse tumor cells (Chromatin MudPIT data)

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The Elongation Factor and Histone Chaperone Spt6 Maintains ESC Pluripotency by Controlling Super-Enhancers and Counteracting Polycomb Repressive Complex 2

Project description:Spt6 coordinates nucleosome dis- and re-assembly, transcriptional elongation and mRNA processing. Here, we report that depleting Spt6 in ESCs reduced expression of pluripotency factors, increased expression of cell lineage-affiliated developmental regulators, and induced cell morphological and biochemical changes indicative of ESC differentiation. Selective down-regulation of pluripotency factors upon Spt6 depletion may be mechanistically explained by its enrichment at ESC super-enhancers where Spt6 controlled H3K27 acetylation and methylation, and super-enhancer RNA transcription. In ESCs, Spt6 interacted with the PRC2 core subunit Suz12 and prevented H3K27me3 accumulation at ESC super-enhancers and associated promoters. Biochemical as well as functional experiments revealed that Spt6 could compete for binding of the PRC2 methyltransferase Ezh2 to Suz12 and reduce PRC2 chromatin engagement. Thus, in addition to serving as histone chaperone and transcription elongation factor, Spt6 counteracts repression by opposing H3K27me3 deposition at critical genomic regulatory regions.

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Nascent Transcript Folding Plays a Major Role in Determining RNA Polymerase Elongation Rates

Project description:Transcription elongation rates influence RNA processing, but sequence-specific regulation is poorly understood. We addressed this in vivo, analyzing RNAPI in S. cerevisiae. Mapping RNAPI by Miller chromatin spreads or UV crosslinking revealed 5′ enrichment and strikingly uneven local polymerase occupancy along the rDNA, indicating substantial variation in transcription speed. Two features of the nascent transcript correlated with RNAPI distribution: folding energy and GC content in the transcription bubble. In vitro experiments confirmed that strong RNA structures close to the polymerase promote forward translocation and limit backtracking, whereas high GC in the transcription bubble slows elongation. A mathematical model for RNAPI elongation confirmed the importance of nascent RNA folding in transcription. RNAPI from S. pombe was similarly sensitive to transcript folding, as were S. cerevisiae RNAPII and RNAPIII. For RNAPII, unstructured RNA, which favors slowed elongation, was associated with faster cotranscriptional splicing and proximal splice site use, indicating regulatory significance for transcript folding.

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