A genetic framework for RNAi inheritance in Caenorhabditis elegans

Gene regulation by RNA interference (RNAi) is a conserved process driven by double-stranded RNA (dsRNA). It responds to exogenous cues and drives endogenous gene regulation. In Caenorhabditis elegans, RNAi can be inherited from parents to offspring. While a number of factors have been implicated in this inheritance process, we do not understand how and when they function. Using a new inheritance assay, we establish a hierarchy amongst previously identified inheritance factors. The nuclear argonaute protein HRDE-1 was required for RNAi establishment in parents and offspring, but not for the inheritance process. In contrast, the cytoplasmic argonaute protein WAGO-3 was the only factor essential for inheritance, via sperm and oocyte, while not affecting establishment in either parent or offspring. We propose a cycle between nuclear and cytoplasmic argonaute proteins, where nuclear activity drives most of the silencing and cytoplasmic activity ensures inheritance. Finally, we implicate the RNA helicase ZNFX-1 as a factor that controls the entry of exogenous versus endogenous small RNAs into this cycle, ensuring a proper balance between gene silencing and activity.