The dynamic process by which nuclear RNAi engages a transcriptionally active target, before the repressive state is stably established, remains largely a mystery. Here, we found that the onset of exogenous dsRNA-induced nuclear RNAi in C. elegans is a transgenerational process, and it requires a putative histone methyltransferase (HMT), SET-32. By developing a CRISPR-based genetic approach, we found that silencing establishment at the endogenous targets of germline nuclear RNAi also requires SET-32. Although SET-32 and two H3K9 HMTs, MET-2 and SET-25, are dispensable for the maintenance of silencing, they do contribute to transcriptional repression in mutants that lack the germline nuclear Argonaute protein HRDE-1, suggesting a conditional role of heterochromatin in the maintenance phase. Our study indicates that (1) establishment and maintenance of siRNA-guided transcriptional repression are two distinct processes with different genetic requirements and (2) the rate-limiting step of the establishment phase is a transgenerational, chromatin-based process. Deciphering mechanisms of transgenerational epigenetic gene regulation is critical for understanding of development, aging, and disease. In this study, Kalinava et al. examine the establishment of RNAi-mediated epigenetic silencing. The identification of the bottleneck step provides critical insight into the regulation of this pathway.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)
- epigenetic silencing
- nuclear RNAi
- silencing establishment
- transgenerational epigenetic inheritance