An intriguing characteristic of imprinted genes is that they often cluster in large chromosomal domains, raising the possibility that gene-specific and domain-specific mechanisms regulate imprinting. Several common features emerged from comparative analysis of four imprinted domains in mice and humans: (a) Certain genes appear to be imprinted by secondary events, possibly indicating a lack of gene-specific imprinting marks; (b) some genes appear to resist silencing, predicting the presence of cis-elements that oppose domain-specific imprinting control; (c) the nature of the imprinting mark remains incompletely understood. In addition, common silencing mechanisms are employed by the various imprinting domains, including silencer elements that nucleate and propagate a silent chromatin state, insulator elements that prevent promoter-enhancer interactions when hypomethylated on one parental allele, and antisense RNAs that function in silencing the overlapping sense gene and more distantly located genes. These commonalities are reminiscent of the behavior of genes subjected to, and the mechanisms employed in, dosage compensation.

中文翻译：

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基因组印迹：簇中表观遗传调控的复杂性。

印迹基因的一个有趣特征是它们通常聚集在较大的染色体结构域中，从而增加了基因特异性和结构域特异性机制调节印迹的可能性。通过对小鼠和人类中四个印迹区域的比较分析，发现了几个共同的特征：（a）某些基因似乎被继发性事件所印迹，这可能表明缺乏基因特异性的印迹标记；（b）一些基因似乎可以抵抗沉默，预测顺式元件的存在与域特异的印迹控制相反；（c）印迹标记的性质仍未完全理解。此外，各种刻印域采用了常见的沉默机制，包括使成核并传播沉默染色质状态的沉默子元件，当在一个亲本等位基因上被低甲基化时，可防止启动子-增强子相互作用的绝缘子元件，以及可使重叠的有义基因和更远距离的基因沉默的反义RNA。这些共同点使人联想到经受剂量补偿的基因的行为以及所采用的机制。