Reik W, Walter J
Laboratory of Developmental Genetics and Imprinting, Babraham Institute, Cambridge, UK.
Curr Opin Genet Dev. 1998 Apr;8(2):154-64. doi: 10.1016/s0959-437x(98)80136-6.
Imprinting is a genetic mechanism that determines expression or repression of genes according to their parental origin. Some imprinted genes occur in clusters in the genome. Recent work using transgenic mice shows that multiple cis-acting sequences are needed for correct imprinting. Mutation analysis in a normal chromosomal context reveals the importance of imprinting centres for regional establishment or maintenance of imprinting in a cluster. Elements that contribute to the function of imprinting centres and regional propagation of the imprints are CpG-rich differentially methylated regions (that during development retain germline imposed methylation or demethylation), direct repeat clusters, and unusual RNAs (antisense, non-translated etc.). The interaction of these cis elements with transacting factors such as methylase and chromatin factors establishes a hierarchical control system with local and regional effects.
印记是一种遗传机制，它根据基因的亲本来源决定基因的表达或抑制。一些印记基因在基因组中以簇的形式出现。最近利用转基因小鼠进行的研究表明，正确的印记需要多个顺式作用序列。在正常染色体背景下的突变分析揭示了印记中心对于区域印记在簇中的建立或维持的重要性。对印记中心功能和印记区域传播有贡献的元件包括富含CpG的差异甲基化区域（在发育过程中保留种系施加的甲基化或去甲基化）、直接重复簇和异常RNA（反义RNA、非翻译RNA等）。这些顺式元件与诸如甲基化酶和染色质因子等反式作用因子的相互作用建立了一个具有局部和区域效应的分级控制系统。
