PRC1和PRC2在着床前胚胎发育中的分工

Division of labor:different tasks for PRC1 and PRC2 in preimplantation embryos

Epigenetic regulation on gene expression is key to the decision and maintenance of cell fates during development.One of the oldest and the most explored epigenetic machinery involves the Polycomb group(PcG)proteins,which regulate a plethora of critical biological processes,including chromatin organization,X chromosome inactivation,proliferation and differentiation,and tumorigenesis.The functions of PcG proteins are further diversified by the highly sophisticated multi-subunit complex assembly like LEGOs[1].Biochemically,PcG proteins assemble into two major complexes with unique chromatin-modifying activities:Polycomb repressive complex(PRC)1 and PRC2.PRC1 contains a core involving E3 ubiquitin ligases RING1A and RING1B,and catalyzes monoubiquitination on lysine 119 of histone H2A(H2AK119ub1),whereas PRC2 catalyzes mono-,di-,and tri-methylation on lysine 27 of histone H3(H3K27me1/2/3).Although PRC1 and PRC2 cooperate intimately in mediating transcriptional silencing,emerging evidence suggests independent roles at a subset of PcG targets.Recently,Zhu et al.[2]revealed distinct requirements for H2AK119ub1 and H3K27me3 to repress the expression of canonical PcG targets and DNA methylation-independent non-canonical imprinting genes,respectively,during early embryonic development.