piRNA-mediated silencing of exogenous retrovirus in mouse spermatogonial stem cells.

Viral integration into germline cells poses a transgenerational threat to genome stability, yet protective mechanisms remain unclear. We demonstrate that Trp53 and PIWI-interacting RNAs (piRNAs) are essential for antiviral defense through regulation of the cancer-testis antigen MAGEA5. Transient viral infection in spermatogonial stem cells (SSCs) induces piRNAs, which are perturbed in Trp53-or Piwil2-deficient SSCs. This disruption increases viral expression and reduces histone H3 lysine 9 trimethylation and DNA methylation at long terminal repeats. Antisense piRNA production is largely absent in stably infected SSCs, suggesting that piRNA expression patterns reflect prior viral exposure. Additionally, cancer testis antigens that form complexes with TRIM28 and inhibit TRP53 are downregulated in Trp53-or Piwil2-deficient SSCs via increased microRNAs, facilitating viral gene expression and integration. Furthermore, Trp53 deficiency enhances lentiviral transmission through the germline. Our findings uncover a piRNA-MAGEA5-TRP53 axis as a key molecular safeguard that restricts viral invasion and preserves germline integrity.