Kubiura-Ichimaru Musashi, Ito Takamasa, Lefebvre Louis, Tada Masako
Stem Cells & Reprogramming Laboratory, Department of Biology, Faculty of Science, Toho University, Miyama 2-2-1, Funabashi, Chiba, 274-8510, Japan.
Department of Medical Genetics, Molecular Epigenetics Group, Life Sciences Institute, University of British Columbia, Vancouver, V6T 1Z3, Canada.
Chromosome Res. 2021 Jun;29(2):145-157. doi: 10.1007/s10577-020-09645-y. Epub 2020 Nov 17.
DNA methylation is an essential epigenetic mark that regulates normal mammalian embryonic development. DNA methylation profiles are not always static, especially during germline development. In zygotes, DNA is typically highly methylated but, during preimplantation, DNA methylation is erased globally. Then, at the start of post-implantation development in mouse embryos, DNA again becomes dramatically hypermethylated. Chromatin structure regulates the accessibility of DNA-modifying enzymes to target DNA. Beyond that, however, our understanding of the pathway by which chromatin regulation initiates changes in global DNA methylation during mouse embryonic development remains incomplete. To analyse the relationship between global regulation of DNA methylation and chromatin status, we examined 5-methylcytosine (5mC), modified by the DNA methyltransferase DNMT, and the oxidative derivative 5-hydroxymethylation (5hmC), converted from 5mC by TET-family enzymes, by means of immunofluorescence staining of mitotic chromosomes in mouse embryonic stem cells (ESCs). Our comparison of immunostaining patterns for those epigenetic modifications in wild-type, DNMT-deficient, and TET-deficient ESCs allowed us to visualise cell cycle-mediated DNA methylation changes, especially in euchromatic regions. Our findings suggest that DNA methylation patterns in undifferentiated mouse ESCs are stochastically balanced by the opposing effects of two activities: demethylation by TET and subsequent remethylation by DNMT.
DNA甲基化是一种重要的表观遗传标记，可调节正常的哺乳动物胚胎发育。DNA甲基化谱并非总是静态的，尤其是在生殖系发育过程中。在受精卵中，DNA通常高度甲基化，但在植入前阶段，DNA甲基化会整体消除。然后，在小鼠胚胎植入后发育开始时，DNA再次显著超甲基化。染色质结构调节DNA修饰酶对目标DNA的可及性。然而，除此之外，我们对染色质调节在小鼠胚胎发育过程中引发全局DNA甲基化变化的途径的理解仍然不完整。为了分析DNA甲基化的全局调节与染色质状态之间的关系，我们通过对小鼠胚胎干细胞（ESC）有丝分裂染色体进行免疫荧光染色，检测了由DNA甲基转移酶DNMT修饰的5-甲基胞嘧啶（5mC）以及由TET家族酶将5mC转化而来的氧化衍生物5-羟甲基化（5hmC）。我们对野生型、DNMT缺陷型和TET缺陷型ESC中这些表观遗传修饰的免疫染色模式进行比较，使我们能够观察到细胞周期介导的DNA甲基化变化，尤其是在常染色质区域。我们的研究结果表明，未分化的小鼠ESC中的DNA甲基化模式通过两种相反活动的作用随机平衡：TET介导的去甲基化和随后DNMT介导的重新甲基化。
