Mammalian Developmental Epigenetics Group, Institut Curie, CNRS UMR3215, INSERM U934, PSL University, Paris, France.
Instituto de Medicina Molecular, João Lobo Antunes, Faculdade de Medicina, Universidade de Lisboa, Lisboa, Portugal.
EMBO Rep. 2019 Oct 4;20(10):e48019. doi: 10.15252/embr.201948019. Epub 2019 Aug 27.
Xist RNA has been established as the master regulator of X-chromosome inactivation (XCI) in female eutherian mammals, but its mechanism of action remains unclear. By creating novel Xist-inducible mutants at the endogenous locus in male mouse embryonic stem (ES) cells, we dissect the role of the conserved A-B-C-F repeats in the initiation of XCI. We find that transcriptional silencing can be largely uncoupled from Polycomb repressive complex 1 and complex 2 (PRC1/2) recruitment, which requires B and C repeats. Xist ΔB+C RNA specifically loses interaction with PCGF3/5 subunits of PRC1, while binding of other Xist partners is largely unaffected. However, a slight relaxation of transcriptional silencing in Xist ΔB+C indicates a role for PRC1/2 proteins in early stabilization of gene repression. Distinct modules within the Xist RNA are therefore involved in the convergence of independent chromatin modification and gene repression pathways. In this context, Polycomb recruitment seems to be of moderate relevance in the initiation of silencing.
Xist RNA 已被确定为雌性真哺乳类动物 X 染色体失活 (XCI) 的主要调控因子，但它的作用机制仍不清楚。通过在雄性小鼠胚胎干细胞 (ES) 细胞的内源性基因座上创建新型的 Xist 诱导突变体，我们剖析了保守的 A-B-C-F 重复在 XCI 起始中的作用。我们发现转录沉默可以与多梳抑制复合物 1 和复合物 2 (PRC1/2) 的募集基本分离，这需要 B 和 C 重复。Xist ΔB+C RNA 特异性失去与 PRC1 的 PCGF3/5 亚基的相互作用，而其他 Xist 伴侣的结合则基本不受影响。然而，Xist ΔB+C 中转录沉默的轻微放松表明 PRC1/2 蛋白在早期基因抑制的稳定中起作用。因此，Xist RNA 内的不同模块参与了独立的染色质修饰和基因抑制途径的收敛。在这种情况下，多梳蛋白募集在沉默的起始中似乎具有中等重要性。
