Evidence for a Temporal Window of Argonaute Surveillance Prior to mRNA Translation in the C. Elegans Germline

Abstract

Piwi Argonautes and their piRNA co-factors silence transposons in animal germlines. However, little is known about whether and how piRNAs regulate other germline-expressed mRNAs. Here we explore Piwi-mediated gene regulation in C. elegans. We show that mRNAs expressed within a common cytoplasm and with identical piRNA-targeted regions, can nevertheless differ in their sensitivity to piRNA silencing. Sensitivity was largely determined by the coding region of the mRNA, exclusive of the promoter, introns, and untranslated regions (UTRs). We show that piRNA scanning occurs independently, or upstream, of nonsense-mediated-decay (NMD), a pathway that mediates surveillance of transcripts for premature stop codons. Our findings reveal that C. elegans piRNAs provide incremental regulation on germline-expressed genes and suggest that piRNA scan mRNAs prior to ribo some access, likely during transit through peri-nuclear germline nuage.