Abstract
PIWI-interacting RNAs (piRNAs) play critical and conserved roles in transposon silencing and gene regulation in the animal germline. Two distinct piRNA populations are present during mouse spermatogenesis: pre-pachytene piRNAs in fetal/neonatal testes and pachytene piRNAs in adult testes. PNLDC1 is required for both pre-pachytene piRNA and pachytene piRNA 3' end maturation in multiple species. However, whether PNLDC1 is the bona fide piRNA trimmer and the physiological role of 3' trimming of two distinct piRNA populations in spermatogenesis remain unclear. Here, by inactivating Pnldc1 exonuclease activity in vitro and in mice, we reveal that PNLDC1 trimmer activity is required for both pre-pachytene piRNA and pachytene piRNA 3' end trimming and male fertility. Furthermore, conditional inactivation of Pnldc1 in postnatal germ cells causes LINE1 transposon de-repression and spermatogenic arrest in mice. This indicates that pachytene piRNA trimming, but not pre-pachytene piRNA trimming, is essential for mouse germ cell development and transposon silencing. Our findings highlight the potential of inhibiting germline piRNA trimmer activity as a potential means for male contraception.