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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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Project description:The nucleolus is a membraneless organelle responsible for ribosome biogenesis, perinuclear heterochromatin formation, and genome stability regulation. However, how cell fate decision occurs, including early embryonic development, ESC differentiation, and tumorigenesis, remains poorly understood at the nucleolar level. It has been observed that large nucleoli and rDNA hyperactivity are common in pluripotent stem cells and tumor cells, while the nucleolus shrinks and rDNA transcriptional activity decrease during lineage commitment. iPSCs nucleolar size and rDNA transcriptional activity are greater than that before reprogramming. It remains unclear how and when the differentiated cell nucleoli convert to the stem cell nucleoli during iPSC reprogramming.In this study, we found that nucleolar remodeling, manifested as enlarged nucleolus, activation of rDNA transcription, enhanced activity of nucleolar organizing regions (NORs), and conversion of reticular nucleolar ultrastructure into low-granular, is an early and stage-specific event that occurs during iPSCs reprogramming. Our study highlights the importance of rDNA transcriptional activity in the early stages of iPSC reprogramming, which is crucial for nucleolar remodeling and regaining stemness. Interfering rDNA transcription hinders nucleolar remodeling, which has disastrous consequences for chromatin remodeling in early stage of iPSC reprogramming and iPSCs establishment. Moreover, our results revealed a nucleolar regulation on chromatin accessibility during iPSC reprogramming and identified some candidate genes (Mybl2, Bard1 and other chromosome related genes) that might be associated with iPSC reprogramming, which may apply to nucleolar remodeling in other cell fated decision.

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

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