The intermitochondrial cement (IMC) and chromatoid body (CB) are posited as central sites for piRNA activity in mice, with MIWI initially assembling in the IMC for piRNA processing before translocating to the CB for functional deployment. The regulatory mechanism underpinning MIWI translocation, however, has remained elusive. We unveil that piRNA loading is the trigger for MIWI translocation from the IMC to CB. Mechanistically, piRNA loading facilitates MIWI release from the IMC by weakening its ties with the mitochondria-anchored TDRKH. This, in turn, enables arginine methylation of MIWI, augmenting its binding affinity for TDRD6 and ensuring its integration within the CB. Notably, loss of piRNA-loading ability causes MIWI entrapment in the IMC and its destabilization in male germ cells, leading to defective spermatogenesis and male infertility in mice. Collectively, our findings establish the critical role of piRNA loading in MIWI translocation during spermatogenesis, offering new insights into piRNA biology in mammals.

线粒体间水泥（IMC）和类染色质体（CB）被认为是小鼠 piRNA 活性的中心位点，MIWI 最初在 IMC 中组装进行 piRNA 处理，然后转移到 CB 进行功能部署。然而，支持 MIWI 易位的调控机制仍然难以捉摸。我们发现 piRNA 加载是 MIWI 从 IMC 易位到 CB 的触发因素。从机制上讲，piRNA 负载通过削弱 MIWI 与线粒体锚定的 TDRKH 的联系，促进 MIWI 从 IMC 中释放。这反过来又使 MIWI 的精氨酸甲基化，增强其与 TDRD6 的结合亲和力并确保其在 CB 中的整合。值得注意的是，piRNA 负载能力的丧失会导致 MIWI 被 IMC 捕获并在雄性生殖细胞中不稳定，从而导致小鼠精子发生缺陷和雄性不育。总的来说，我们的研究结果证实了 piRNA 负载在精子发生过程中 MIWI 易位中的关键作用，为哺乳动物中 piRNA 生物学提供了新的见解。