Dissecting the Antiviral Role of MUT-7

Abstract

RNA interference (RNAi) is an antiviral defense mechanism that protects Caenorhabditis elegans against RNA virus infection. MUT-7, a conserved 3′ to 5′ exoribonuclease, has been shown to be involved in RNAi pathway, yet its mechanistic role in antiviral immunity remains incompletely understood. In this study, we investigate the functional contribution of MUT-7 in the context of antiviral defense in C. elegans. Preliminary data in the Kennedy lab demonstrates that MUT-7 exhibits a noncanonical substrate preference, binding double-stranded RNA (dsRNA) and selectively degrading one strand of dsRNA substrates with paired 3′ ends. This activity distinguishes MUT-7 from canonical 3′ exoribonucleases, which typically act on single-stranded RNA with accessible 3′ termini. These findings suggest that MUT-7 may bind and degrade double-stranded viral RNA intermediates generated by viral RdRPs so that MUT-7 can slow or even inhibit viral replication. To assess the role of MUT-7 in antiviral defense, we measured viral load in wild-type, mut-7 loss-of-function, and catalytically dead mutant strains following Orsay virus infection. Loss of MUT-7 results in increased viral RNA levels, consistent with a role in restricting viral replication. However, RNA immunoprecipitation results suggest that MUT-7 doesn’t associate with viral RNAs directly, which might suggest that MUT-7 has either a transient interaction or no interaction with viral RNAs. Another interesting result is that viral load is lower when both MUT-7 and RDE-1 are not present compared to when only RDE-1 is not present, which might suggest that MUT-7 acts upstream of RDE-1 in antiviral defense. Together, our results support that MUT-7 is required for antiviral defense in C. elegans, but the mechanism is still unclear.