Decreased SynMuv B gene activity in response to viral infection leads to activation of the antiviral RNAi pathway in C. elegans

Small RNA pathways regulate eukaryotic antiviral defense. Many of the Caenorhabditis elegans mutations that were identified based on their enhanced RNAi, the synMuv B genes, also emerged from unrelated genetic screens for increased growth factor signaling. The dozen synMuv B genes encode homologues of the mammalian dREAM complex found in nearly all animals and plants, which includes the lin- 35/retinoblastoma oncogene. In wild type animals, a combination of a synMuv A mutation and a synMuv B mutation are required for the Muv phenotype of increased growth factor signaling. But we showed that Orsay virus infection of a single synMuv A mutant can induce a Muv phenotype, unlike the uninfected single synMuv A mutant. This suggests that decreased synMuv B activity, which activates the antiviral RNAi pathway, is a defense response to viral infection. This study presents small RNA deep sequencing analysis of various dREAM complex mutants uncovering distinct siRNA profiles indicative of such an siRNA response. Small RNA high-throughput sequencing was done on wild-type, glp-4, and synmuv mutant strains of C. elegans. Total RNA was isolated from cell lysates from adult C. elegans cultured at 20˚C (glp-4+) or 25˚C (glp-4-). Small RNA data was processed using the tinyRNA pipeline.