RNA interference in Fasciola hepatica newly excysted juveniles: Long dsRNA induces more persistent silencing than siRNA

In trematodes RNA interference is the current tool of choice for functional analysis of genes since classical reverse genetic approaches remain unavailable. Whereas this approach has been optimized in schistosomes, few reports are available for other trematodes, likely reflecting the difficulties in the establishment of the technology. Here we standardized conditions for RNAi in the liver fluke Fasciola hepatica, the causative agent of fasciolosis, one of the most problematic infections affecting livestock worldwide. Targeting a single copy gene, encoding leucine aminopeptidase (LAP) as a model, we refined delivery conditions which identified electro-soaking, i.e. electroporation and subsequent incubation as efficient for introduction of small RNAs into the fluke. Knock down of LAP was achieved with as little as 2.5 μg/ml dsRNA concentrations, which may reduce or obviate off-target effects. However, at these concentrations, tracking incorporation by fluorescent labeling was difficult. While both long dsRNA and short interfering RNA (siRNA) are equally effective at inducing a short-term knock down, dsRNA induced persistent silencing up to 21 days after treatment, suggesting that mechanisms of amplification of the interfering signal can be present in this pathogen. Persistent silencing of the invasive stage for up to 3 weeks (close to what it takes for the fluke to reach the liver) opens the possibility of using RNAi for the validation of putative therapeutic targets.