Activation of automethylated PRC2 by dimerization on chromatin

Polycomb Repressive Complex 2 (PRC2) trimethylates lysine 27 of histone 3 (H3K27me3). This modification transcriptionally represses chromatin and its dynamics are essential for embryonic development. PRC2 also methylates its cofactor JARID2 and both methylated H3 tail and JARID2 allosterically activate the complex. PRC2 undergoes auto-methylation of its catalytic subunit, which stimulates its activity by an unknown mechanism. We show that automethylated PRC2 forms a dimer on substrate chromatin that results in autoactivation in trans. An inactive PRC2 protomer distal to the substrate nucleosome serves as an allosteric activator of the second PRC2 protomer, which is poised to methylate H3. Functional assays support our model of allosteric activation via dimerization, suggesting a novel mechanism of PRC2 trans-autoactivation that may be important for installation of H3K27me3 into naïve chromatin. Overall design: To investigate PRC2-mediated effects during retinoic acid-driven cell differentiation, we established Ezh2 rescue cell lines in Ezh1-/-;Ezh2-/- murine embryonic stem cells (N/A Strain of origin 129P2/Ola; Lavarone etal., 2019) and analysed transcriptomic changes over the course of 4 days. To investigate PRC2-mediated effects during retinoic acid-(RA-)driven cell differentiation, we established SUZ12 rescue cell lines in SUZ12-/- murine embryonic stem cells and analysed transcriptomic changes over the course of 4 days.