Male fertility and sperm development are thermosensitive processes whereby germline exposure to high temperature reduces viable sperm. Small RNAs and Argonaute proteins play critical roles in male fertility, particularly at high temperature conditions. In C. elegans, several small RNA pathways function in spermatogenic germlines and target germline expressed mRNAs. Argonaute CSR-1 targets many spermatogenesis genes and recent evidence highlights a dual role for CSR-1 in mRNA protection and mRNA clearance, the second requiring CSR-1 catalytic activity to slice mRNA targets. Whether and how these distinct functions of CSR-1 promote male fertility remains largely unkown. Intriguingly, a germline enriched helicase RNA helicase A (RHA-1) is also required for male thermosensitive fertility. Here we show that, in
rha-1 mutants, CSR-1 small RNAs exhibit a slight decrease in overall abundance. The CSR-1 small RNAs are preferentially depleted from the coding sequence rather than the 3' UTR of target mRNAs, similar to the reported CSR-1 small RNA defects found in CSR-1 slicer mutant. When analyzing the mRNA levels of CSR-1 target genes,
rha-1 mutants show increased CSR-1 mRNA targets, including spermatogenesis genes. Taken together, our results suggest RHA-1 facilitates CSR-1 slicing of mRNA transcripts to promote mRNA clearance. Our study further highlights the critical role of small RNA-mediated mRNA clearance in sperm fertility.