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The PIWI/piRNA machinery has been implicated as an innate immune system that prevents the activity of mobile genetic elements from destabilizing DNA in animal germ cells.Recent studies have advanced our understanding of the biogenesis and function of this machinery; however, its metabolism has remained largely unexplored.Here, we show that murine PIWI (MIWI) is degraded through the APC/C-26S proteasome pathway, and that piRNAs play an indispensable role in this process by enhancing MIWI interaction with the APC/C substratebinding subunit.Interestingly, piRNA-triggered MIWI destruction occurs in late stages of spermatogenesis, which in turn leads to piRNA elimination, suggesting a feed-forward mechanism for coordinated removal of the MIWI/piRNA machinery at a specific developmental stage.Importantly, the proper removal of MIWI/piRNA is essential for sperm maturation.Together, our results reveal a novel and unexpected role of piRNAs in regulating the clearance of the MIWI/piRNA machinery via the ubiquitin-proteosome pathway, and demonstrate the critical importance of proper temporal regulation of MIWI/piRNA in male germ cell development.