The ribonuclease DISL-2 mediates piRNA degradation in C. elegans.

The PIWI/piRNA pathway acts as a conserved RNA-directed immune mechanism that suppresses transposons and promotes fertility. The biogenesis of piRNAs has been extensively investigated, yet the mechanisms governing piRNA degradation remain poorly understood. Here, we systematically measure the half-lives of thousands of Caenorhabditis elegans piRNAs, revealing a broad range from less than 1 h to over 20 h. Notably, piRNAs with 3' terminal uridines (U) degrade faster than those ending in 3' guanines or cytosines, suggesting that terminal nucleotides modulate piRNA stability. We identify DISL-2, a 3' to 5' exoribonuclease as a key enzyme for degrading piRNAs with templated 3' uridines and non-templated 3' uridines, the latter catalyzed by poly(U) polymerase PUP-1. Furthermore, DISL-2 acts as a quality control factor to target piRNAs that are improperly processed. Together, these findings advance our understanding of piRNA homeostasis by determining piRNA half-lives and identifying factors responsible for piRNA decay.