Lymphocyte Development, MRC London Institute of Medical Sciences (LMS), Du Cane Road, London W12 0NN, UK.
Lymphocyte Development, MRC London Institute of Medical Sciences (LMS), Du Cane Road, London W12 0NN, UK
Philos Trans R Soc Lond B Biol Sci. 2017 Nov 5;372(1733). doi: 10.1098/rstb.2016.0358.
X-chromosome inactivation (XCI) is an exemplar of epigenetic regulation that is set up as pluripotent cells differentiate. Once established, XCI is stably propagated, but can be reversed or by pluripotent reprogramming Although reprogramming provides a useful model for inactive X (Xi) reactivation in mouse, the relative instability and heterogeneity of human embryonic stem (ES) cells and induced pluripotent stem cells hampers comparable progress in human. Here we review studies aimed at reactivating the human Xi using different reprogramming strategies. We outline our recent results using mouse ES cells to reprogramme female human fibroblasts by cell-cell fusion. We show that pluripotent reprogramming induces widespread and rapid chromatin remodelling in which the human Xi loses and H3K27m3 enrichment and selected Xi genes become reactivated, ahead of mitotic division. Using RNA sequencing to map the extent of human Xi reactivation, and chromatin-modifying drugs to potentiate reactivation, we outline how this approach could be used to better design strategies to re-express human X-linked loci. As cell fusion induces the expression of human pluripotency genes that represent both the 'primed' and 'naive' states, this approach may also offer a fresh opportunity to segregate human pluripotent states with distinct Xi expression profiles, using single-cell-based approaches.This article is part of the themed issue 'X-chromosome inactivation: a tribute to Mary Lyon'.
X 染色体失活 (XCI) 是表观遗传调控的一个范例,它在多能细胞分化时建立。一旦建立,XCI 就会稳定地传播,但可以通过多能重编程 或逆转。尽管重编程为小鼠中失活 X (Xi) 的激活提供了一个有用的模型,但人类胚胎干细胞 (ES) 和诱导多能干细胞的相对不稳定性和异质性阻碍了在人类中取得类似的进展。在这里,我们回顾了使用不同重编程策略来激活人类 Xi 的研究。我们概述了我们最近使用小鼠 ES 细胞通过细胞融合重编程雌性人类成纤维细胞的结果。我们表明,多能重编程诱导广泛而快速的染色质重塑,其中人类 Xi 失去 和 H3K27m3 富集,选择的 Xi 基因在有丝分裂分裂之前被重新激活。使用 RNA 测序来绘制人类 Xi 重新激活的程度,并使用染色质修饰药物来增强重新激活,我们概述了如何使用这种方法更好地设计重新表达人类 X 连锁基因座的策略。由于细胞融合诱导表达人类多能基因,这些基因代表“启动”和“幼稚”状态,因此这种方法也可能为使用单细胞为基础的方法分离具有不同 Xi 表达谱的人类多能状态提供新的机会。本文是主题为“X 染色体失活:献给 Mary Lyon 的颂歌”的特刊的一部分。