Ups and downs of RNA interference in parasitic nematodes.

RNA interference (RNAi) is widely used in Caenorhabiditis elegans to identify essential gene function. In parasitic nematodes RNAi has been reported to result in transcript knockdown of some target genes, but not others, thus limiting its use as a potential functional genomics tool. We recently extended work in Haemonchus contortus to examine why only some genes seem to be susceptible to RNAi and to test RNAi effects in vivo. Here we review our findings, which suggest that site of gene expression influences silencing. This most likely reflects limited uptake of dsRNA from the environment, a phenomenon also observed in other free-living nematodes. We discuss new technologies to improve dsRNA delivery, such as nanoparticles being developed for therapeutic siRNA delivery, and methods to monitor RNAi effects. Alternative approaches will be important in progressing the application of RNAi to identify essential gene function in parasitic nematodes.