Zili is required for germ cell differentiation and meiosis in zebrafish

Small RNAs exert an effect through diverse RNA interference pathways to transcriptionally or post‐transcriptionally silence their targets. The Piwi‐interacting RNAs (piRNAs) represent a germline‐specific small RNA pathway where Piwi proteins themselves are thought to mediate piRNA biosynthesis. Here, we provide strong evidence for a piRNA amplification loop in zebrafish, in which Ziwi and Zili bind piRNAs of opposite polarity. Furthermore, we describe a function for Zili in transposon defense and germ cell differentiation, as well as a crucial function in meiosis, significantly extending the function of Piwi proteins beyond the control of transposable elements in vertebrates.