Distinct and collaborative functions of Yb and Armitage in transposon-targeting piRNA biogenesis

PIWI-interacting RNAs (piRNAs) repress transposons to maintain germline genome integrity. Previous studies showed that artificial tethering of Armitage (Armi) to reporter RNAs induced piRNA biogenesis. However, lack of female sterile (1) Yb (Yb) in Drosophila ovarian somatic cells (OSCs) impaired production of transposon-targeting piRNAs even in the presence of Armi. Here, we show that specific interaction of Armi with RNA transcripts of flamenco piRNA cluster, the primary source of transposon-targeting piRNAs in OSCs, is strictly regulated by Yb. Lack of Yb allowed Armi to bind RNAs promiscuously, leading to the production of piRNAs unrelated to transposon silencing. The ATP hydrolysis-defective mutants of Armi failed to unwind RNAs and were retained on them, abolishing piRNA production. These findings shed light on distinct and collaborative requirements of Yb and Armi in transposon-targeting piRNA biogenesis. We also provide evidence supporting the direct involvement of Armi but not Yb in Zucchini-dependent piRNA phasing. Armi-associated RNAs characterized by FAST-iCLIP and CLIPPARE, and Piwi-associated small RNA levels in OSCs (Ovarian Somatic Cells)