Milagre Inês, Stubbs Thomas M, King Michelle R, Spindel Julia, Santos Fátima, Krueger Felix, Bachman Martin, Segonds-Pichon Anne, Balasubramanian Shankar, Andrews Simon R, Dean Wendy, Reik Wolf
Epigenetics Programme, The Babraham Institute, Cambridge CB22 3AT, UK.
Epigenetics Programme, The Babraham Institute, Cambridge CB22 3AT, UK.
Cell Rep. 2017 Jan 31;18(5):1079-1089. doi: 10.1016/j.celrep.2017.01.008.
Global DNA demethylation is an integral part of reprogramming processes in vivo and in vitro, but whether it occurs in the derivation of induced pluripotent stem cells (iPSCs) is not known. Here, we show that iPSC reprogramming involves both global and targeted demethylation, which are separable mechanistically and by their biological outcomes. Cells at intermediate-late stages of reprogramming undergo transient genome-wide demethylation, which is more pronounced in female cells. Global demethylation requires activation-induced cytidine deaminase (AID)-mediated downregulation of UHRF1 protein, and abolishing demethylation leaves thousands of hypermethylated regions in the iPSC genome. Independently of AID and global demethylation, regulatory regions, particularly ESC enhancers and super-enhancers, are specifically targeted for hypomethylation in association with transcription of the pluripotency network. Our results show that global and targeted DNA demethylation are conserved and distinct reprogramming processes, presumably because of their respective roles in epigenetic memory erasure and in the establishment of cell identity.
全基因组DNA去甲基化是体内和体外重编程过程的一个组成部分，但诱导多能干细胞（iPSC）的产生过程中是否发生全基因组DNA去甲基化尚不清楚。在此，我们表明iPSC重编程涉及全基因组和靶向去甲基化，这两者在机制和生物学结果上是可分离的。重编程中后期阶段的细胞经历短暂的全基因组去甲基化，在雌性细胞中更为明显。全基因组去甲基化需要激活诱导的胞苷脱氨酶（AID）介导的UHRF1蛋白下调，消除去甲基化会在iPSC基因组中留下数千个高甲基化区域。独立于AID和全基因组去甲基化，调控区域，特别是胚胎干细胞增强子和超级增强子，在多能性网络转录过程中与低甲基化特异性相关。我们的结果表明，全基因组和靶向DNA去甲基化是保守且不同的重编程过程，可能是由于它们在表观遗传记忆消除和细胞身份建立中的各自作用。
