RNA Interference and Nonspecific Controls in Parasitic Helminths

Despite of the remarkable success of RNA interference (RNAi) application in the free-living nematode Caenorhabditis elegans, the exploitation of this powerful technique to helminths parasites with complex life-cycle has been a challenge for parasitologists. It has proved to be effective only for certain parasite species and specific target genes. To date, RNAi is the only methodology available for reverse genetics in trematodes and combined to rescue studies (such heterologous complementation) have been the only alternative to genetic manipulation in nematodes and helminths parasites, thus this subject is of great interest to the scientific community involved in the field. The RNAi technique is widely used to assess gene function in helminths parasites, in order to elucidate their role in parasite development, mechanisms of drug resistance, and validate therapeutic targets for disease control. After fifteen years of the first report of RNAi in parasitic helminths, many advances have been achieved, but pitfalls remain as challenges in gene expression manipulation in these organisms. In addition to the methodological particularities of the RNAi technique for each group of helminths, there are still other reasons behind the slow progress of RNAi in those parasites, such; the lack of homology between genes related to parasitism and genes of model organisms and the complex life cycle of these organisms, which results in difficulties for in vitro cultivation. At this point, a wide assortment of approaches for doubled stranded RNA “delivery” has been proposed. Thus, deeper studies on fundamental aspects of the RNAi methodology in parasitic helminths, such as off-target and the use of controls, can be useful in determining the reason of variations between and within species, facilitating the experimental design and the use of RNAi in the study and eradication of helminths parasites.