Transcription is required for establishment of germline methylation marks at imprinted genes
Transcription is required for establishment of germline methylation marks at imprinted genes
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DOI：
10.1101/gad.495809
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发表时间：
2009-01-01
影响因子：
10.5
通讯作者：
Kelsey, Gavin
中科院分区：
文献类型：
--
作者：
Chotalia, Mita;Smallwood, Sebastien A.;Kelsey, Gavin
基因组印记需要通过雄性和雌性配子中基因的DNA甲基化进行差异标记。在雌性种系中，甲基化印记标记的获得依赖于从头甲基转移酶Dnmt3a及其辅助因子Dnmt3L，但为什么特定序列是Dnmt3a和Dnmt3L的靶标的原因仍然知之甚少。在这里，我们研究了转录在建立母体种系甲基化标记中的作用。我们发现，在Gnas位点，截断最远上游Nesp启动子的转录本会破坏卵母细胞衍生的差异甲基化区域（DMRs）的甲基化。通过DMRs在卵母细胞中的转录并不局限于这个位点，而是发生在许多其他母体标记的印迹结构域的预期DMRs上，这表明转录事件有一个共同的要求。配子甲基化中涉及的转录本是蛋白质编码，而非编码反义转录本则涉及体细胞组织中印迹基因的单等位基因沉默，尽管它们通常由卵母细胞中的替代启动子启动。我们认为转录是从头甲基化系统的第三个重要组成部分，其中包括最佳CpG间距和组蛋白修饰，并且可能需要创建或维持开放的染色质结构域，以允许甲基化复合物进入其首选目标。
Genomic imprinting requires the differential marking by DNA methylation of genes in male and female gametes. In the female germline, acquisition of methylation imprint marks depends upon the de novo methyltransferase Dnmt3a and its cofactor Dnmt3L, but the reasons why specific sequences are targets for Dnmt3a and Dnmt3L are still poorly understood. Here, we investigate the role of transcription in establishing maternal germline methylation marks. We show that at the Gnas locus, truncating transcripts from the furthest upstream Nesp promoter disrupts oocyte-derived methylation of the differentially methylated regions (DMRs). Transcription through DMRs in oocytes is not restricted to this locus but occurs across the prospective DMRs at many other maternally marked imprinted domains, suggesting a common requirement for transcription events. The transcripts implicated here in gametic methylation are protein-coding, in contrast to the noncoding antisense transcripts involved in the monoallelic silencing of imprinted genes in somatic tissues, although they often initiate from alternative promoters in oocytes. We propose that transcription is a third essential component of the de novo methylation system, which includes optimal CpG spacing and histone modifications, and may be required to create or maintain open chromatin domains to allow the methylation complex access to its preferred targets.