Discussion

RNA is a dynamic molecule that underpins biological complexity through diverse mechanisms of gene regulation. In plants RNA can transmit information between diverse parasites and plant cells. Research in the last five years demonstrates that parasitic nematodes also release RNAs that get internalized by host (mammalian) cells. We previously showed that the gastrointestinal nematode Heligmosomoides polygyrus bakeri (Hpb) exports small RNAs in extracellular vesicles that are internalized by mouse epithelial and macrophage cells, and these suppress host immune responses in vitro and in vivo. We further showed that raising antibodies against the EVs confers protection to infection, suggesting that EVs are an important mechanism of host modulation. More recently we found that the dominant class of RNAs in EVs is siRNAs generated by RNA-dependent RNA polymerases inside the nematode and there is a specific enrichment in siRNAs derived from novel repetitive and transposable elements. Small RNA sequencing of mouse epithelial cells following EV treatment suggests a subset of the nematode siRNAs and miRNAs are present at functionally relevant concentrations and may interact with host genes with high degrees of complementarity. We further characterize one specific vesicular Argonaute protein (exWAGO) that associates with the siRNAs and mediates their export. Using immunoprecipitation techniques we have developed a method to capture exWAGO in vivo and identify the guide RNAs with which it associates under different environmental conditions. We have also developed methods for directly detected the exWAGO protein and parasite EVs in vivo, providing evidence for RNA transmission from nematode to mouse under physiological conditions.