Germ granule association drives small RNA specificity for a nuclear Argonaute protein [mRNA-seq]
RNA interference (RNAi) is a conserved gene silencing process that exists in diverse organisms to protect genome integrity and regulate gene expression. In C. elegans, majority of RNAi components are located in phase-separated perinuclear germ granules, including P granule, Mutator foci, Z granule, and SIMR foci. However, the protein components and function of the newly discovered SIMR foci are unknown. Here we identified HRDE-2 as a SIMR foci component, which interacts with the germline nuclear RNAi Argonaute HRDE-1. We found that unloaded HRDE-1 localizes to SIMR foci and this localization depends on HRDE-2. In addition, HRDE-2 contributes to HRDE-1 small RNAs binding specificity and, in the absence of HRDE-2, HRDE-1 exclusively loads CSR-class 22G-RNAs rather than WAGO-class 22G-RNAs, promotes H3K9me3 deposition on CSR-targets, but does not silence these CSR-target genes. Thus, our study demonstrates that HRDE-2 is critical to ensure correct small RNAs are used to guide nuclear RNA silencing in the C. elegans germline. Overall design: PolyA-selected RNA from whole worms (from wild-type, hrde-1(tm1200), and hrde-2(qe20)) was used to make mRNA-seq libraries