Transcription Driven Somatic DNA Methylation within the Imprinted Gnas Cluster
Transcription Driven Somatic DNA Methylation within the Imprinted Gnas Cluster
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DOI：
10.1371/journal.pone.0117378
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发表时间：
2015-02-06
期刊：
影响因子：
3.7
通讯作者：
Peters, Jo
中科院分区：
文献类型：
--
作者：
Mehta, Stuti;Williamson, Christine M.;Peters, Jo
通过DNA甲基化对雌、雄配子中基因进行差异标记是基因组印记的关键。在雌性配子中，穿越差异甲基化区域（DMR）的转录是DMR处的从头甲基化的常见要求。在印迹的Gnas簇卵母细胞处，蛋白质编码转录物Nesp的特异性转录对于Nesp基因内的两个DMR（即Nespas-Gnasxl DMR和外显子1A DMR）的甲基化是需要的，从而使得Gnas转录物的表达和Gnasxl转录物的阻遏成为可能。在父本等位基因上，Nesp被抑制，生殖系DMR未甲基化，Gnas被抑制并且Gnasxl被表达。使用突变小鼠模型，我们表明，在父亲的等位基因，异位转录的NESP穿越基因内外显子1A DMR（调节Gnas的表达）的结果在从头甲基化的外显子1A DMR和去抑制Gnas就像在母亲的等位基因。然而，与母本等位基因不同，突变父本等位基因上的甲基化发生在受精后，即在体细胞中。据我们所知，这是体细胞组织中基因内CpG岛的转录/转录驱动的DNA甲基化的第一个例子，表明转录驱动的从头甲基化不限于小鼠的生殖系。此外，Gnasxl在Nesp异位表达的父本染色体上被抑制。因此，显示Nesp异位表达的父系遗传的Gnas簇在Gnasxl和Gnas表达方面是"母系化的"。我们表明，这些小鼠具有与具有两种表达剂量的Gnas而没有Gnasxl的突变体相似的表型。
Differential marking of genes in female and male gametes by DNA methylation is essential to genomic imprinting. In female gametes transcription traversing differentially methylated regions (DMRs) is a common requirement for de novo methylation at DMRs. At the imprinted Gnas cluster oocyte specific transcription of a protein-coding transcript, Nesp, is needed for methylation of two DMRs intragenic to Nesp, namely the Nespas-Gnasxl DMR and the Exon1A DMR, thereby enabling expression of the Gnas transcript and repression of the Gnasxl transcript. On the paternal allele, Nesp is repressed, the germline DMRs are unmethylated, Gnas is repressed and Gnasxl is expressed. Using mutant mouse models, we show that on the paternal allele, ectopic transcription of Nesp traversing the intragenic Exon1A DMR (which regulates Gnas expression) results in de novo methylation of the Exon1A DMR and de-repression of Gnas just as on the maternal allele. However, unlike the maternal allele, methylation on the mutant paternal allele occurs post-fertilisation, i.e. in somatic cells. This, to our knowledge is the first example of transcript/transcription driven DNA methylation of an intragenic CpG island, in somatic tissues, suggesting that transcription driven de novo methylation is not restricted to the germline in the mouse. Additionally, Gnasxl is repressed on a paternal chromosome on which Nesp is ectopically expressed. Thus, a paternally inherited Gnas cluster showing ectopic expression of Nesp is "maternalised" in terms of Gnasxl and Gnas expression. We show that these mice have a phenotype similar to mutants with two expressed doses of Gnas and none of Gnasxl.