Argonautes promote male fertility and provide a paternal memory of germline gene expression in C. elegans

During each life cycle germ cells preserve and pass on both genetic and epigenetic information. In C. elegans, the ALG-3/4 Argonaute (AGO) proteins and their small-RNA cofactors are expressed during male gametogenesis and promote male fertility. Here we show that the CSR-1 AGO functions with ALG-3/4 to positively regulate target genes required for spermiogenesis. Our findings suggest that ALG-3/4 functions during spermatogenesis to amplify a small-RNA signal that represents an epigenetic memory of male-specific gene expression, while CSR-1, which is abundant in mature sperm, transmits this memory to offspring. Surprisingly, in addition to small RNAs targeting male-specific genes, we show that males also harbor an extensive repertoire of CSR-1 small RNAs targeting oogenesis-specific mRNAs. Together these findings suggest that C. elegans sperm transmit not only the genome but also epigenetic binary signals in the form of Argonaute/small-RNA complexes that constitute a memory of which genes were active in preceding generations. Overall design: Examine small RNA changes in WT and alg-3/4 mutant males cultured at 20°C and 25°C, as well as determine the small RNAs enriched in a FLAG::CSR-1 IP from male worms grown at 25°C. mRNA sequencing was also performed to determine how transcripts targeted by small RNAs change in mutant background at 20°C and 25°C.