EZHIP constrains Polycomb Repressive Complex 2 activity in germ cells

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ABSTRACT The Polycomb machinery is required for the proper orchestration of gene expression by virtue of its critical role in maintaining transcriptional silencing. It is composed of several chromatin modifying complexes, including Polycomb Repressive Complex 2 (PRC2), which deposits H3K27me2/3. Here, we report the identification of a new cofactor of PRC2, EZHIP (EZH1/2 Inhibitory Protein), expressed predominantly in the gonads. EZHIP limits the enzymatic activity of PRC2 and lessens the interaction between the core complex and its accessory subunits, but does not interfere with PRC2 recruitment to chromatin. Deletion of Ezhip leads to a global increase in H3K27me2/3 deposition both during spermatogenesis and at late stages of oocyte maturation. This alteration of the epigenetic content of mature oocytes does not affect the initial number of follicles but is associated with a reduction of follicles in aging mice. We provide evidences that mature oocytes Ezhip -/- are not fully functional and that fertility is strongly impaired in Ezhip -/- females. Altogether, our study uncovers EZHIP as a novel functional player in the comprehensive chromatin remodeling that occurs in the gonads.

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