Lepidopteran immunity and parasite manipulation: The role of host gap junctions and their viral analogues

Gap junctions in animals provide intercellular communication between adjacent cells, coordinating multicellular behaviors, by selective transfer of small molecules such as cAMP, Ca²⁺, and ATP. Insect gap junctions are structurally comprised by the Innexin proteins, while innexin homologues have been identified from polydnaviruses associated with parasitic wasps. Our studies have shown that innexins are present in fat body and hemocytes, suggesting that gap junction communication is necessary for proper immune responses – and that alteration will disrupt immunity. We have investigated the characteristics of a hemocyte-expressed innexin (Spodoptera frugiperda innexin2, Sf-inx2) and multiple vinnexins. Using confocal microscopy we have demonstrated that Sf-Inx2 and Cs-VnxD co-localize to the appositional membranes of High-Five cells, suggesting innexin-vinnexin interactions occur during the formation of gap junctions. In addition, electrophysiology studies demonstrate that four tested vinnexins and Sf-Inx2 are capable of forming functional gap junctions. Current electrophysiology and microscopic studies are being performed to address whether co-expression of a vinnexin affects Inx2 gap junction characteristics. Also, biochemical studies are being performed to address potential protein interactions between the innexins and vinnexins. Together, these studies will provide critical steps toward understanding the basic biology that takes place during a lepidopteran immune response and the mechanisms of parasite manipulation.