Tandem repeat hypothesis in imprinting:: Deletion of a conserved direct repeat element upstream of H19 has no effect on imprinting in the Igf2-H19 region
Tandem repeat hypothesis in imprinting:: Deletion of a conserved direct repeat element upstream of H19 has no effect on imprinting in the Igf2-H19 region
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DOI：
10.1128/mcb.24.13.5650-5656.2004
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发表时间：
2004-07-01
影响因子：
5.3
通讯作者：
Reik, W
中科院分区：
文献类型：
--
作者：
Lewis, A;Mitsuyaj, K;Reik, W
Igf 2和H19是位于小鼠远端7号染色体上的双印记基因。它们共享几个调控元件，包括H19上游的差异甲基化区域（DMR），其在整个发育过程中父系甲基化。将DNA甲基化靶向DMR的顺式作用序列要求仍然未知;然而，已经提出可能涉及DMR附近的直接串联重复。以前的研究印记Rasgrf 1基因座确实表明，一个直接重复元件相邻的DMR是负责建立父系等位基因特异性甲基化的DMR，因此等位基因表达的Rasgrf 1转录。我们确定了一个突出的和保守的直接串联重复1 kb上游的H19 DMR，并提出，它发挥了类似的作用，印迹调节H19。为了检验我们的假设，我们产生了携带1.7-kb定向重复元件缺失的小鼠，并分析了胎儿生长、等位基因表达和Igf 2-H19区域内的甲基化。令人惊讶的是，删除对印迹没有影响。这些结果与其他重复序列的删除接近印迹基因表明，直接重复序列可能是不重要的，在大多数印迹位点的甲基化的目标，Rasgrf 1位点可能是一个例外，这一规则。
Igf2 and H19 are reciprocally imprinted genes on mouse distal chromosome 7. They share several regulatory elements, including a differentially methylated region (DMR) upstream of H19 that is paternally methylated throughout development. The cis-acting sequence requirements for targeting DNA methylation to the DMR remain unknown; however, it has been suggested that direct tandem repeats near DMRs could be involved. Previous studies of the imprinted Rasgrf1 locus demonstrate indeed that a direct repeat element adjacent to a DMR is responsible for establishing paternal allele-specific methylation at the DMR and therefore allelic expression of the Rasgrf1 transcript. We identified a prominent and conserved direct tandem repeat 1 kb upstream of the H19 DMR and proposed that it played a similar role in imprinted regulation of H19. To test our hypothesis, we generated mice harboring a 1.7-kb targeted deletion of the direct repeat element and analyzed fetal growth, allelic expression, and methylation within the Igf2-H]9 region. Surprisingly the deletion had no effect on imprinting. These results together with deletions of other repeats close to imprinted genes suggest that direct repeats may not be important for the targeting of methylation at the majority of imprinted loci and that the Rasgrf1 locus may be an exception to this rule.