Gene editing in the nematode parasite Nippostrongylus brasiliensis using extracellular vesicles to deliver active Cas9/guide RNA complexes

Abstract

Despite recent advances, animal-parasitic nematodes have thus far been largely refractory to genetic manipulation. We describe here a new approach providing proof of principle that CRISPR/Cas9-mediated gene editing of parasitic nematodes is achievable using vesicular stomatitis virus glycoprotein-pseudotyped extracellular vesicles (EV) for the delivery of Cas9-synthetic guide RNA (RNP) complexes. We demonstrate that EV-delivered RNPs can be used to disrupt a secreted DNase II in Nippostrogylus brasiliensis. Introduction of a repair template encoding multiple stop codons led to measurable reduction in expression of the targeted gene. Altered transcripts corresponding to the edited locus were detected by RT-PCR, demonstrating that vesicles can access cells of tissues actively expressing the gene of interest. These data provide evidence that this technique can be employed for targeted gene editing in N. brasiliensis, making this species genetically tractable for the first time and providing a new platform for genetic analysis of parasitic nematodes. Author SummaryParasitic nematodes have a complex life cycle involving passage through a host organism, which makes them very difficult to manipulate genetically. Recently, a method for deleting, changing or replacing genes (gene editing) has been developed in other organisms which has revolutionised our ability to understand fine details of how these organisms work. It has generally not been possible to adapt this method to parasitic nematodes because delivery of the components is difficult, and this has proved to be a bottleneck in understanding how parasites develop, survive and interact with their host. We show here that the components for gene editing can be introduced into a widely used laboratory model of intestinal nematode infection by encapsulation in membrane-bound vesicles which have been modified to carry a protein which facilitates fusion of the vesicles with parasite cells and delivery of the contents. This resulted in accurate editing of a specific gene by deletion and repair, such that the amount of functional protein produced from that gene was reduced. This system should be applicable to all nematode species, and will facilitate understanding of their complex biology, in addition to defining new targets for control of infection.