Authors

F Chow⁵; G Koutsovoulos³; C O Vazquez⁶; J R Bermúdez Barrientos⁶; D Laetsch³; S Kumar⁴; J Claycomb²; M Blaxter¹; C A Goodger⁶; A Buck⁷;  ¹ Centre for Immunity, Infection and Evolution, School of Biological Sciences. University of Edinburgh, UK;  ² Department of Molecular Genetics, University of Toronto, Canada;  ³ Institute of Evolutionary Biology and Centre for Immunology, Infection and Evolution, University of Edinburgh, UK;  ⁴ Institute of Immunology & Infection Research, University of Edinburgh, UK;  ⁵ Institute of Immunology and Infection Research, University of Edinburgh, UK;  ⁶ Langebio – Cinvestav, Irapuato, GTO, Mexico;  ⁷ University of Edinburgh, UK

Discussion

RNA interference pathways underpin defence and adaptation strategies in nematodes, but their roles in parasitism are largely unexplored. We previously showed that the gastrointestinal nematode Heligmosomoides polygyrus bakeri (Hpb) exports small RNAs in extracellular vesicles that are internalized by mouse 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 EVs are an important mechanism of host modulation. Here we report the full spectrum of small RNAs in these vesicles, based on a new assembly and annotation of the Hpb genome. 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 selective 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 that is highly conserved in the parasitic species but rapidly diverged in free-living Caenorhabditis and confirm its presence in other parasitic strongyle extracellular products. Our findings point to selectivity in the loading of newly evolved siRNAs in EVs from nematode parasites and suggest a novel Argonaute protein may mediate this.