MUT-14 and SMUT-1 DEAD Box RNA Helicases Have Overlapping Roles in Germline RNAi and Endogenous siRNA Formation

Abstract

Summary More than two thousand C. elegans genes are targeted for RNA silencing by the mutator complex, a specialized siRNA amplification module which is nucleated by the Q/N-rich protein MUT-16. The mutator complex localizes to Mutator foci adjacent to P granules at the nuclear periphery in germ cells [1]. Here, we show that the DEAD box RNA helicase smut-1 functions redundantly in the mutator pathway with its paralog mut-14 during RNA interference. Mutations in both smut-1 and mut-14 also cause widespread loss of endogenous siRNAs. The targets of mut-14 and smut-1 largely overlap with the targets of other mutator class genes, however, the mut-14 smut-1 double mutant and the mut-16 mutant display the most dramatic depletion of siRNAs, suggesting that they act at a similarly early step in siRNA formation, mut-14 and smut-1 are predominantly expressed in the germline and, unlike other mutator class genes, are specifically required for RNAi targeting germline genes. A catalytically inactive, dominant negative missense mutant of MUT-14 is RNAi-defective in vivo, however, mutator complexes containing the mutant protein retain the ability to synthesize siRNAs in vitro. The results point to a role for mut-14 and smut-1 in initiating siRNA amplification in germ cell Mutator foci, possibly through the recruitment or retention of target mRNAs.

RNA helicase HEL-1 promotes longevity by specifically activating DAF-16/FOXO transcription factor signaling in Caenorhabditis elegans

“…The sacy-1 gene functions as a negative regulator of meiotic maturation (33). smut-1 plays roles in the formation of endogenous siRNA (34). The function of ZK512.2 is not known in either C. elegans or mammals.…”

Reproducible features of small RNAs in C. elegans reveal NU RNAs and provide insights into 22G RNAs and 26G RNAs

“…These included the CSR-1 class genes (Tu et al 2015) that generate abundant 22G RNAs that are bound by the Argonaute CSR-1, the WAGO-1 class genes (Tu et al 2015) that generate abundant 22G RNAs that are bound by the Argonaute WAGO-1, and the MUT class genes (Phillips et al 2014) that require Mutator proteins such as MUT-16 to generate abundant 22G RNAs. In data sets where abundant NU-RNAs could be detected, genes of CSR-1 class, WAGO-1 class, or MUT class all had NU RNAs (Supplemental Fig.…”

Emerging from the Clouds: Vasa Helicase Sheds Light on piRNA Amplification

“…Could this particular role for DEAD box helicases, or Vasa in particular, be conserved in small RNA processing in other organisms? Other recent work has demonstrated roles for three DEAD box helicases that localize to RNA granules in the germline 22G-small RNA pathway and exogenous RNAi in Caenorhabditis elegans (Phillips et al, 2014;Yang et al, 2014;Shirayama et al, 2014). 22G-RNAs differ from piRNAs in their amplification mechanism, but nonetheless, specific DEAD box helicases could be utilized in a manner similar to Vasa to load Argonaute in germ granules.…”