RNF17 referees ping-pong in mouse testes [smallRNAseq]

In mammals, piRNA populations are dynamic throughout male germ cell development. Embryonic piRNAs consist of both primary and secondary species and are mainly directed toward transposons. In meiotic cells, however, the piRNA population is transposon-poor and restricted to primary piRNAs derived from pachytene piRNA clusters. The mechanism controlling which piRNAs are present at each developmental stage is poorly understood. Here we show that RNF17 shapes adult meiotic piRNA content by suppressing the production of secondary piRNAs. In the absence of RNF17, ping-pong (secondary amplification) occurs inappropriately in meiotic cells, aberrantly targeting protein-coding genes and lncRNAs. Our data indicate that RNF17 comprises one component of a "refereeing" mechanism that prevents deleterious activity of the meiotic piRNA pathway by ensuring the selective loading of PIWI proteins with products of meiotic piRNA clusters. Examination of small RNA profile in heterozygous and homozygous RNF17 adult testes, pachytene or round spermatid sorted cells在哺乳动物体内，Piwi互作RNA（piRNA）的群体动态变化贯穿雄性生殖细胞发育的整个进程。胚胎阶段的piRNA同时包含初级与次级两种亚型，且主要靶向转座子。然而在减数分裂细胞中，piRNA群体几乎不含转座子，且仅包含源自粗线期piRNA簇的初级piRNA。目前学界对调控不同发育阶段piRNA组成的分子机制仍知之甚少。本研究证实，RNF17通过抑制次级piRNA的生成，塑造成年减数分裂期的piRNA组成。当RNF17缺失时，减数分裂细胞中会异常激活乒乓循环（ping-pong，次级扩增）机制，异常靶向蛋白编码基因与长链非编码RNA（lncRNAs）。本研究数据表明，RNF17是一套“审核”机制的组成部分，该机制通过确保PIWI蛋白选择性加载减数分裂piRNA簇的产物，从而阻断减数分裂piRNA通路的有害活性。本研究对杂合及纯合RNF17基因型成年睾丸、分选的粗线期细胞或圆形精子细胞的小RNA谱展开了分析。