Functional proteomics identified a PICS complex required for piRNA maturation and chromosome segregation

Piwi-interacting RNAs (piRNAs) play significant roles in suppressing transposons and nonself nucleic acids, maintaining genome integrity, and defending against viral infections, and are essential for fertility in a variety of organisms. In C. elegans, most piRNA precursors are transcribed by RNA polymerase II in the nucleus and are subjected to a number of processing and maturation steps. However, the biogenesis of piRNAs is still not fully understood. We used functional proteomics to study piRNA biogenesis in C. elegans and identified a piRNA processing and chromosome segregation (PICS) complex. The PICS complex contains two known piRNA biogenesis factors, TOFU-6 and PID-1, and three new proteins PICS-1, TOST-1, and ERH-2, which exhibit dynamic localization among different subcellular compartments. In the germlines of gravid animals, the PICS complex contains TOFU-6/PICS-1/ERH-2/PID-1, is largely concentrated at the perinuclear granule zone and engages in piRNA processing. During early embryogenesis, the TOFU-6/PICS-1/ERH-2/TOST-1 complex accumulates in the nucleus and plays essential roles in chromosome segregation and cell division. Interestingly, the functions of these factors in mediating chromosome segregation are independent of piRNA production. Therefore, we speculate that differential compositions of PICS factors may help cells coordinate distinct cellular processes. In this study, we compared total small RNAs from (1) control animals; (2) tofu-6 mutants; (3) pics-1 mutants;(4)erh-2 mutants; (5)tost-1 mutants; (6)prg-1 mutants