The Nuclear Argonaute NRDE-3 Contributes to Transitive RNAi in Caenorhabditis elegans

摘要

The Caenorhabditis elegans >nuclear >RNA interference >defective (Nrde) mutants were identified by their inability to silence polycistronic transcripts in >enhanced >RNA>i () mutant backgrounds. Here, we report additional -dependent RNAi phenomena that extend the mechanisms, roles, and functions of nuclear RNAi. We show that mutants are broadly RNAi deficient and that overexpressing enhances RNAi. Consistent with being a dose-dependent limiting resource for effective RNAi, we find that is required for eri-dependent enhanced RNAi phenotypes, although only for a subset of target genes. We then identify as an additional limiting RNAi resource important for eri-dependent silencing of a nonoverlapping subset of target genes, so that an ; ; triple mutant fails to show enhanced RNAi for any tested gene. These results suggest that and define separate and independent limiting RNAi resource pathways. Limiting RNAi resources are proposed to primarily act via endogenous RNA silencing pathways. Consistent with this, we find that mutants misexpress genes regulated by endogenous siRNAs and incompletely silence repetitive transgene arrays. Finally, we find that contributes to transitive RNAi, whereby amplified silencing triggers act in trans to silence sequence-similar genes. Because nrde-dependent silencing is thought to act in cis to limit the production of primary transcripts, this result reveals an unexpected role for nuclear processes in RNAi silencing.