Extracellular vesicles : an arsenal in the interspecies war

International audience

English. Parasitoid wasps are insects that have a specialized lifestyle: the adult is a free-living organism, but their developmental stages are parasitic. The female lays an egg on or in a host and the egg develops in and at the expense of that host. To ensure successful development of their offspring, female wasps must suppress the host's immune response and regulate its physiology. In particular, endoparasitoids develop inside the host and use extracellular vesicles (EVs) to transport and deliver virulence molecules (DNA or proteins) into specific host cells. Depending on the species, the parasitoid wasp injects different types of EVs, which have different origins: they are either produced in specialized cells in the ovaries or in the venom gland. The most studied EVs are found in braconid species and have been named PolyDnaViruses (PDV) because these particles are produced using domesticated endogenous viruses. These virus-like particles carry circular DNA molecules encoding wasp proteins that are expressed and act in host tissues. A second type of EVs, which also involves the machinery of an integrated endogenous virus, is produced in the ovaries of the wasp Venturia canescens (ichneumonid parasitoids of lepidopteran larvae) and are called virus-like particles (VLPs). These vesicles differ from PDVs in that they contain only proteins. The third type, which we have named "venosomes", are membrane vesicles of about 150-200 nm produced in the venom gland of very few parasitoid species, including Leptopilina species, figitid wasps that parasitize Drosophila larvae, and Meteorus pulchricornis (Braconidae) that parasitizes Lepidoptera caterpillars. Venosomes are used to transport specific proteins into host immune cells, where they interfere with the encapsulation response, which consists of cell aggregation around the parasitoid egg and subsequent melanization of this capsule to kill it. Our team has contributed to the characterization of these EVs and has acquired knowledge on the nature and evolution of some of the proteins transported. The main challenge will now be to investigate the evolutionary origin of these venosomes and, in particular, to understand their peculiar biogenesis, the exact mechanisms of their targeting to host cells and the mechanisms underlying the changes they induce in the host cells.