Two molecular features contribute to the Argonaute specificity for the microRNA and RNAi pathways in C. elegans.

In Caenorhabditis elegans, specific Argonaute proteins are dedicated to the RNAi and microRNA pathways. To uncover how the precise Argonaute selection occurs, we designed dsRNA triggers containing both miRNA and siRNA sequences. While dsRNA carrying nucleotides mismatches can only enter the miRNA pathway, a fully complementary dsRNA successfully rescues let-7 miRNA function and initiates silencing by RNAi. We demonstrated that RDE-1 is essential for RNAi induced by the perfectly paired trigger, yet is not required for silencing by the let-7 miRNA. In contrast, ALG-1/ALG-2 are required for the miRNA function, but not for the siRNA-directed gene silencing. Finally, a dsRNA containing a bulged miRNA and a perfectly paired siRNA can enter both pathways suggesting that the sorting of small RNAs occurs after that the dsRNA trigger has been processed by Dicer. Thus, our data suggest that the selection of Argonaute proteins is affected by two molecular features: (1) the structure of the small RNA duplex; and (2) the Argonautes specific characteristics.

RNAi pathway in C. elegans: the argonautes and collaborators.

Since Dr. Sidney Brenner first used it as an animal model system, the round worm Caenorhabditis elegans has significantly contributed to our understanding of important biological processes. Among them, the discovery in the 1990s of new gene silencing pathways orchestrated by tiny non-coding RNAs created a new field of research in biology. In this review, we will discuss the key players of the RNAi pathways in C. elegans and particularly the Argonaute genes, an impressive gene family of 27 members important in many aspects of these pathways.