CTCF mediates methylation-sensitive enhancer-blocking activity at the H19/Igf2 locus
CTCF mediates methylation-sensitive enhancer-blocking activity at the H19/Igf2 locus
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DOI：
10.1038/35013106
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发表时间：
2000-05-25
期刊：
影响因子：
64.8
通讯作者：
Tilghman, SM
中科院分区：
文献类型：
--
作者：
Hark, AT;Schoenherr, CJ;Tilghman, SM
胰岛素样生长因子2 （Igf2）和H19基因被印迹，分别导致母本和父本等位基因沉默。这一事件依赖于H19上游2千碱基的印迹控制区（参考文献1,2）。在父系染色体上，该元件被甲基化，是H19沉默所必需的（参考文献2-4）。在母体染色体上，该区域未甲基化，需要在上游90千碱基处沉默Igf2基因(2)。我们提出，未甲基化的印迹控制区作为染色质边界，阻断Igf2与H19 3′增强子的相互作用（文献5,6）。当该区域甲基化时，这种增强子阻断活性就会丧失，从而允许Igf2的父系表达。通过转基因小鼠和组织培养，我们发现小鼠和人类H19未甲基化的印迹控制区表现出增强子阻断活性。此外，我们发现CTCF，一种与脊椎动物边界功能有关的锌指蛋白(7)，与未甲基化的印迹控制区的几个位点结合，这些位点对增强子阻断至关重要。与我们的模型一致，DNA甲基化消除了CTCF的结合。据我们所知，这是脊椎动物中染色质边界调控的第一个例子。
The Insulin-like growth factor 2 (Igf2) and H19 genes are imprinted, resulting in silencing of the maternal and paternal alleles, respectively. This event is dependent upon an imprinted-control region two kilobases upstream of H19 (refs 1, 2). On the paternal chromosome this element is methylated and required for the silencing of H19 (refs 2-4). On the maternal chromosome the region is unmethylated and required for silencing of the Igf2 gene 90 kilobases upstream(2). We have proposed that the unmethylated imprinted-control region acts as a chromatin boundary that blocks the interaction of Igf2 with enhancers that lie 3' of H19 (refs 5, 6). This enhancer-blocking activity would then be lost when the region was methylated, thereby allowing expression of Igf2 paternally. Here we show, using transgenic mice and tissue culture, that the unmethylated imprinted-control regions from mouse and human H19 exhibit enhancer-blocking activity. Furthermore, we show that CTCF, a zinc finger protein implicated in vertebrate boundary function(7), binds to several sites in the unmethylated imprinted-control region that are essential for enhancer blocking. Consistent with our model, CTCF binding is abolished by DNA methylation. This is the first example, to our knowledge, of a regulated chromatin boundary in vertebrates.