Raw data for figures.

PIWI-interacting RNAs (piRNAs) play critical and conserved roles in transposon silencing and gene regulation in the animal germline. Three distinct piRNA populations are present during mouse spermatogenesis: fetal piRNAs in fetal/perinatal testes, pre-pachytene and pachytene piRNAs in postnatal testes. PNLDC1 is required for piRNA 3’ end maturation in multiple species. However, whether PNLDC1 is the bona fide piRNA trimmer and the physiological role of 3’ trimming of different piRNA populations in spermatogenesis in mammals remain unclear. Here, by inactivating Pnldc1 exonuclease activity in vitro and in mice, we reveal that the PNLDC1 trimmer activity is essential for spermatogenesis and male fertility. PNLDC1 catalytic activity is required for both fetal and postnatal piRNA 3’ end trimming. Despite this, postnatal piRNA trimming but not fetal piRNA trimming is critical for LINE1 transposon silencing. Furthermore, conditional inactivation of Pnldc1 in postnatal germ cells causes LINE1 transposon de-repression and spermatogenic arrest in mice, indicating that germline-specific postnatal piRNA trimming is essential for transposon silencing and germ cell development. Our findings highlight the germ cell-intrinsic role of PNLDC1 and piRNA trimming in mammals to safeguard the germline genome and promote fertility.

PIWI蛋白互作RNA（PIWI-interacting RNAs）在动物生殖系的转座子沉默与基因调控过程中发挥关键且保守的作用。小鼠精子发生过程中存在三类截然不同的piRNA群体：胎儿/围产期睾丸中的胎儿piRNA，以及出生后睾丸中的粗线前期piRNA与粗线期piRNA。PNLDC1是多种物种中piRNA 3'端成熟过程所必需的因子。然而，PNLDC1是否为名副其实的piRNA修剪酶，以及哺乳动物精子发生过程中不同piRNA群体的3'端修剪的生理功能，目前仍不明确。本研究通过在体外及小鼠体内失活Pnldc1的外切酶活性，证实PNLDC1的修剪酶活性对精子发生与雄性生育能力至关重要。PNLDC1的催化活性同时是胎儿与出生后piRNA 3'端修剪过程所必需的。尽管如此，仅出生后piRNA的修剪而非胎儿piRNA的修剪对LINE1转座子沉默具有关键作用。进一步研究发现，在出生后生殖细胞中条件性失活Pnldc1可导致小鼠出现LINE1转座子去抑制与精子发生阻滞，这表明生殖细胞特异性的出生后piRNA修剪对转座子沉默与生殖细胞发育不可或缺。本研究结果凸显了哺乳动物中PNLDC1与piRNA修剪的生殖细胞内在功能，其可保护生殖系基因组并促进生育能力。