Retroelements comprise a major fraction of most mammalian genomes. To protect their fitness and stability, hosts must keep retroelements in check in their germline. In most tissues mobile element insertions are decorated with chromatin modifications suggestive of transcriptional silencing. However, germline cells undergo massive chromatin reprogramming events, which erase repressive chromatin marks and necessitate de novo re-establishment of silencing. How do host genomes achieve the discrimination necessary for this de novo silencing? A series of recent studies have revealed aspects of the multi-pronged strategy that mammalian genomes use to identify and silence retroelements. These strategies include the use of small RNA-guides, of specialized DNA-binding protein adaptors and of proteins that repair chromatin discontinuities caused by retroelement insertions. Genetic analyses reveal the importance of these mechanisms of protection, each of which specializes in silencing retroelements of different evolutionary ages. Together, these strategies allow mammalian genomes to withstand the high burden of their parasites.

中文翻译：

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捉迷藏：基于染色质的途径如何使哺乳动物生殖系中的逆转录元件沉默。

逆转录元件构成大多数哺乳动物基因组的主要部分。为了保护它们的健康和稳定性，宿主必须在它们的种系中检查逆转录因子。在大多数组织中，移动元件插入被染色质修饰修饰，暗示转录沉默。然而，生殖系细胞会经历大量的染色质重编程事件，这会消除抑制性染色质标记并需要从头重新建立沉默。宿主基因组如何实现这种从头沉默所需的区分？最近的一系列研究揭示了哺乳动物基因组用来识别和沉默逆转录元件的多管齐下策略的各个方面。这些策略包括使用小 RNA 引导，专门的 DNA 结合蛋白接头和修复由逆转录元件插入引起的染色质不连续性的蛋白质。遗传分析揭示了这些保护机制的重要性，每一种机制都专门用于沉默不同进化时代的逆转录因子。总之，这些策略使哺乳动物基因组能够承受寄生虫的高负担。