Aphidius ervi teratocytes release Enolase (Ae-ENO) and Fatty Acid Binding Protein (Ae-FABP) by exosomal vesicles

The molecular bases of the host-parasitoid interactions in the biological system Acyrthosiphon pisum (Harris) (Homoptera, Aphididae) - Aphidius ervi (Haliday) (Hymenoptera, Braconidae) have been elucidated allowing the identification of maternal (a GGT contained in venom secretion) and embryonic parasitic factors (Teratocytes) that regulate the host physiology after parasitization. Teratocytes, cells deriving from the dissociation of the embryonic serosa of the parasitoid, are responsible for an extra-oral digestion of the host tissues in order to provide a suitable nutritional environment for the parasitoid larva development. Teratocytes rapidly grow in size without undergoing any cell division, synthesize, and release in the host hemolymph two proteins: a Fatty Acid Binding Protein (Ae-FABP) involved in transport of fatty acids deriving from host tissues, towards the parasitoid larva, and an Enolase (Ae-ENO). Ae-ENO, is a glycolytic enzyme that, as extracellular protein, works as a plasminogen like receptor inducing its activation in plasmin. Both Ae-FABP and Ae-ENO are released in extracellular environment although their amino acid sequences lack of the signal peptide. Here we investigated the mechanism by which teratocytes release Ae-FABP and Ae-ENO. Our results, obtained by western blot analyses and immunogold staining, demonstrate that these two proteins are localized in vesicles released in vitro by teratocytes. Moreover, immunofluorescence and immunogold assays using an antibody against the protein ALIX (ALG-2 interacting protein X,) confirm the exosomal nature of these vescicles. Indeed immunogold staining clearly show that Alix is localized in the cytoplasm of the teratocytes, in their membrane blebs and into the vesicles released from them. Alix together with other proteins such as TSG101, HSP70 and the tetraspanins CD63, CD81 and CD9 are considered and for this reason commonly used as a marker to identify and discriminate exosomes among different types of extracellular vesicles