Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Cambridge CB2 1QN, UK ; Wellcome Trust/MRC Stem Cell Institute, University of Cambridge, Cambridge CB2 1QR, UK ; Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge CB2 3EG, UK.
Wellcome Trust/MRC Stem Cell Institute, University of Cambridge, Cambridge CB2 1QR, UK.
Stem Cell Reports. 2013 Dec 17;1(6):518-31. doi: 10.1016/j.stemcr.2013.11.010. eCollection 2013.
Pluripotent stem cells (PSCs) occupy a spectrum of reversible molecular states ranging from a naive ground-state in 2i, to metastable embryonic stem cells (ESCs) in serum, to lineage-primed epiblast stem cells (EpiSCs). To investigate the role of DNA methylation (5mC) across distinct pluripotent states, we mapped genome-wide 5mC and 5-hydroxymethycytosine (5hmC) in multiple PSCs. Ground-state ESCs exhibit an altered distribution of 5mC and 5hmC at regulatory elements and dramatically lower absolute levels relative to ESCs in serum. By contrast, EpiSCs exhibit increased promoter 5mC coupled with reduced 5hmC, which contributes to their developmental restriction. Switch to 2i triggers rapid onset of both the ground-state gene expression program and global DNA demethylation. Mechanistically, repression of de novo methylases by PRDM14 drives DNA demethylation at slow kinetics, whereas TET1/TET2-mediated 5hmC conversion enhances both the rate and extent of hypomethylation. These processes thus act synergistically during transition to ground-state pluripotency to promote a robust hypomethylated state.
多能干细胞 (PSCs) 占据了从 2i 中的原始状态到血清中的稳定胚胎干细胞 (ESCs) 再到谱系启动的内细胞团干细胞 (EpiSCs) 的可逆分子状态谱。为了研究 DNA 甲基化 (5mC) 在不同多能状态下的作用，我们在多种 PSCs 中绘制了全基因组 5mC 和 5-羟甲基胞嘧啶 (5hmC) 的图谱。原始状态的 ESCs 在调控元件处表现出 5mC 和 5hmC 的改变分布，并且相对于血清中的 ESCs，绝对水平显著降低。相比之下，EpiSCs 表现出启动子 5mC 的增加伴随着 5hmC 的减少，这导致了它们的发育限制。转换到 2i 会迅速引发原始状态基因表达程序和全局 DNA 去甲基化。从机制上讲，PRDM14 对从头甲基转移酶的抑制以缓慢的动力学驱动 DNA 去甲基化，而 TET1/TET2 介导的 5hmC 转化增强了去甲基化的速度和程度。这些过程在向原始状态多能性的转变过程中协同作用，促进了强大的低甲基化状态。
