National Institute of Biological Sciences, Beijing 102206, China.
Cell Res. 2011 Mar;21(3):442-65. doi: 10.1038/cr.2011.23. Epub 2011 Feb 15.
DNA methylation is an important epigenetic mark involved in diverse biological processes. In plants, DNA methylation can be established through the RNA-directed DNA methylation pathway, an RNA interference pathway for transcriptional gene silencing (TGS), which requires 24-nt small interfering RNAs. In mammals, de novo DNA methylation occurs primarily at two developmental stages: during early embryogenesis and during gametogenesis. While it is not clear whether establishment of DNA methylation patterns in mammals involves RNA interference in general, de novo DNA methylation and suppression of transposons in germ cells require 24-32-nt piwi-interacting small RNAs. DNA methylation status is dynamically regulated by DNA methylation and demethylation reactions. In plants, active DNA demethylation relies on the repressor of silencing 1 family of bifunctional DNA glycosylases, which remove the 5-methylcytosine base and then cleave the DNA backbone at the abasic site, initiating a base excision repair (BER) pathway. In animals, multiple mechanisms of active DNA demethylation have been proposed, including a deaminase- and DNA glycosylase-initiated BER pathway. New information concerning the effects of various histone modifications on the establishment and maintenance of DNA methylation has broadened our understanding of the regulation of DNA methylation. The function of DNA methylation in plants and animals is also discussed in this review.
DNA 甲基化是一种重要的表观遗传标记，参与多种生物学过程。在植物中，DNA 甲基化可以通过 RNA 指导的 DNA 甲基化途径建立，这是一种用于转录基因沉默（TGS）的 RNA 干扰途径，需要 24 个核苷酸的小干扰 RNA。在哺乳动物中，从头 DNA 甲基化主要发生在两个发育阶段：早期胚胎发生和配子发生。虽然目前尚不清楚哺乳动物中 DNA 甲基化模式的建立是否普遍涉及 RNA 干扰，但新生 DNA 甲基化和生殖细胞中转座子的抑制需要 24-32 个核苷酸的 piwi 相互作用小 RNA。DNA 甲基化状态通过 DNA 甲基化和去甲基化反应动态调节。在植物中，活性 DNA 去甲基化依赖于沉默抑制物 1 家族的双功能 DNA 糖苷酶，它去除 5-甲基胞嘧啶碱基，然后在碱基缺失部位切割 DNA 骨架，启动碱基切除修复（BER）途径。在动物中，已经提出了多种活性 DNA 去甲基化的机制，包括脱氨酶和 DNA 糖苷酶起始的 BER 途径。关于各种组蛋白修饰对 DNA 甲基化建立和维持的影响的新信息，拓宽了我们对 DNA 甲基化调控的理解。本文还讨论了 DNA 甲基化在植物和动物中的功能。
