RNAi mediated silencing of actin expression in adult Litomosoides sigmodontis is specific, persistent and results in a phenotype.

In this report, the actin gene from the rodent filaria Litomosoides sigmodontis was successfully knocked down by RNA interference (RNAi). By establishing controls for measuring off-target RNAi effects we showed that lower concentrations of double stranded RNA (dsRNA) are more effective than those previously reported. While all tested concentrations reduced Ls-act transcription, the concentration that consistently reduced Ls-act expression to <10% of the controls was 3.5 microM, a 10-fold lower concentration than that used previously for Brugia malayi. The knockdown of Ls-act was specific as Ls-hsp60 and Ls-gst2 showed no reduction in transcription. Soaking of nematodes with dsRNA coding for the Caenorhabditis elegans yolk receptor (Ce-rme-2), which has no orthologues in filaria, did not affect Ls-act transcription, further demonstrating that the reduction in Ls-act was specific and not due to toxicity of dsRNA or off-target effects. After transferring the nematodes to dsRNA-free medium, the inhibition of Ls-act persisted for at least 72 h, the length of the observation time. Additionally, two phenotypes were seen with Ls-act RNAi. First, adults observed 48 and 72 h after the start of the experiment showed paralysis, as demonstrated by being stretched out and having slower movements. Second, the release of microfilariae was significantly inhibited after soaking with dsRNA. Thus, the use of lower dsRNA concentrations and proper controls for off-target effects make RNAi a viable method to study the function of filarial genes.