Department of Physiology and Cell Biology, University of Nevada School of Medicine, Reno, Nevada, USA.
Biol Reprod. 2012 May 31;86(5):162, 1-14. doi: 10.1095/biolreprod.111.095463. Print 2012 May.
Repetitive sequences, especially transposon-derived interspersed repetitive elements, account for a large fraction of the genome in most eukaryotes. Despite the repetitive nature, these transposable elements display quantitative and qualitative differences even among species of the same lineage. Although transposable elements contribute greatly as a driving force to the biological diversity during evolution, they can induce embryonic lethality and genetic disorders as a result of insertional mutagenesis and genomic rearrangement. Temporary relaxation of the epigenetic control of retrotransposons during early germline development opens a risky window that can allow retrotransposons to escape from host constraints and to propagate abundantly in the host genome. Because germline mutations caused by retrotransposon activation are heritable and thus can be deleterious to the offspring, an adaptive strategy has evolved in host cells, especially in the germline. In this review, we will attempt to summarize general defense mechanisms deployed by the eukaryotic genome, with an emphasis on pathways utilized by the male germline to confer retrotransposon silencing.
重复序列，特别是转座子衍生的分散重复元件，在大多数真核生物的基因组中占很大比例。尽管具有重复性质，但这些可转座元件即使在同一谱系的物种之间也表现出数量和质量上的差异。尽管转座元件作为进化过程中生物多样性的驱动力发挥了巨大作用，但它们会因插入突变和基因组重排而导致胚胎致死和遗传紊乱。在早期生殖细胞发育过程中转座子的表观遗传控制的暂时放松打开了一个危险的窗口，使转座子能够逃脱宿主的限制，并在宿主基因组中大量繁殖。由于反转录转座子激活引起的种系突变是可遗传的，因此可能对后代有害，因此宿主细胞，特别是生殖细胞中进化出了一种适应性策略。在这篇综述中，我们将尝试总结真核基因组所采用的一般防御机制，并特别强调雄性生殖细胞用来沉默反转录转座子的途径。
