RNAi in Haemonchus contortus: a potential method for target validation

RNA interference in parasitic nematodes of animals: a reality check?

“…So, why do parasitic nematodes seem to be less susceptible to RNAi than does C. elegans? Is it because of suboptimal culture conditions and/or methods of double-stranded (ds)RNA delivery -as recently suggested by Zawadzki et al [13] and, if so, is it possible to overcome these hurdles? Alternatively, is the classical RNAi pathway functional in parasitic nematodes and are the effects that have been observed to date caused by as-yet-undefined interactions?…”

“…However, parasitic nematodes will not survive for more than a few days under these conditions, with the result that apparently lethal RNAi phenotypes can arise because the worm is already severely compromised. It is recognized [13] that there is a need to develop appropriate culture conditions that enable the nematode parasite to survive for prolonged periods (weeks or months) or, better still, to continue development through to sexually mature adult worms. For strongyloid parasites such as Haemonchus contortus, the complexity of the medium required to achieve this precludes routine use [15].…”

“…Zawadzki et al [13] attributed the success of RNAi in C. elegans to the ability to maintain the nematode throughout its life cycle. However, other related free-living nematodes (such as Oscheius tipulae and Pristionchus pacificus) that are cultured in a similar way to C. elegans do not seem to be susceptible to gene silencing by RNAi [16].…”

“…[8] and summarized in Ref. [13], is present in parasitic nematodes. In an attempt to understand the limited reliability and efficiency of RNAi in parasitic nematodes, we searched currently available parasite genome and expressed sequence tag (EST) datasets for genes that are known to be involved in the RNAi pathway in C. elegans [23].…”

“…In an attempt to understand the limited reliability and efficiency of RNAi in parasitic nematodes, we searched currently available parasite genome and expressed sequence tag (EST) datasets for genes that are known to be involved in the RNAi pathway in C. elegans [23]. Similar to the results of Zawadzki et al [13], we were unable to identify rde-4, rde-2, sid-2 and rsd-2 homologues in the H. contortus and Brugia malayi genomes (currently 95% and 98% coverage, respectively) and the available nematode EST datasets.…”