What is the Function of Dicers Helicase Domain?
We are exploring the role of Dicer’s helicase domain in C. elegans. We find that the germline defects of C. elegans lacking Dicer (dcr-1(-/-)) are rescued by a transgene encoding wildtype Dicer, as well as by transgenes encoding Dicer with point mutations in the helicase domain. Further, all strains are wildtype in their ability to mount an RNAi response following feeding of exogenous double-stranded RNA (dsRNA). The finding that the helicase mutants were not deficient for exogenous RNAi led us to assay for defects in endogenous small RNA processing. We assayed piRNAs, 4 miRNAs, and 5 endo-siRNAs by northern blot and saw no noticeable defects in processing either piRNAs or miRNAs. However, helicase mutant lines were completely devoid of endo-siRNAs. We also assayed changes in cognate mRNA levels for four of the missing endo-siRNAs, and observed a corresponding increase in mRNA level. To get a more complete picture of the endogenous small RNA defects in our Dicer helicase mutants, we pe
