A tool for repression of RNAi overcomes sterility in Tribolium castaneum.

RNA interference (RNAi) is a natural antiviral defense mechanism in plants and animals. As a counter defense strategy, most viruses have evolved viral suppressors of RNAi (VSRs) to antagonize the RNAi pathway. Here, we utilized transgenic misexpression of a VSR from Cricket Paralysis virus (CrPV1A) to dampen RNAi in a temporal and life-stage specific way in order to overcome limitations of knocking down pleiotropic genes by the strong systemic RNAi response in the red flour beetle Tribolium castaneum. We found that ubiquitously driven VSR rescued the sterility of the females injected with Tc-axin or Tc-decapentaplegic double-stranded RNA, where sterility had previously hampered analysis. By overcoming sterility using this tool and by rescuing zygotic function with a heat-shock driven VSR, we were able to separate maternal from zygotic function for the Wnt pathway inhibitor Tc-Axin. Thereby, we could provide evidence that maternal Wnt signalling alone is responsible for axis formation in Tribolium. Our tool opens new experimental possibilities such as studying genes by parental RNAi, which would normally lead to sterility and separating maternal from zygotic gene functions. Further improvements are required to allow for studying zygotic gene function while rescuing maternal functions and for spatially restricting the RNAi effect.