Internalisation of Leptopilina boulardi venosomes in Drosophila melanogaster lamellocytes : specificity and mechanism.

Leptopilina boulardi wasps are parasitoids that develop inside Drosophila melanogaster larvae by consuming their tissues, leading to the host death. They rely on venom injection at oviposition to circumvent the host immune response and ensure parasitism success. Venom of the ISm strain of L. boulardi mainly targets the main hemocyte type involved in the cellular encapsulation of parasitoid eggs, the lamellocytes, and induce changes in their morphology. We previously demonstrated that venosomes, a specific type of extra-cellular vesicles (EVs) found in LbISm venom are required for parasitism success. Recent data also confirmed that they transport several venom-specific RhoGTPase-activating proteins (e.g. LbGAP and LbGAP2) into the host lamellocytes. However, the host specificity and the mechanism of venosomes entry inside lamellocytes yet remained to be elucidated. Here, we show that venosomes are internalized by lamellocytes at a high level in D. melanogaster (wild type and Hoptuml mutant that constitutively produces numerous lamellocytes) and at a low level in D. yakuba. Whereas they are not found at all in D. suzukii lamellocyte-like cells, suggesting a species-specific mechanism of entry. In D. melanogaster lamellocytes, LbGAP colocalize with endosomal Rab7 protein, suggesting a receptor-mediated endocytosis of venosomes. To characterize the lamellocyte membrane receptor of venosomes, we have set up methods to separate Hoptuml lamellocytes from other hemocytes and purify their membranes. Preliminary results will be presented