The Relationships of parasite Polydnaviruses and Venom Secretions to Host Immunosuppression and Development Arrest

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Some insect parasites that lay eggs in their hosts inject special secretions into the host along with their eggs. These secretions appear to have two effects. First, they protect the parasite's eggs from the host's immune defenses and second, they cause arrest of host development. For Campoletis sonorensis, both phenomena may be induced by a polydnavirus (PDV). PDV is the only animal DNA virus with a heterogeneous, segmented genome. Several viral gene families have been identified, and viral gene expression is tissue and/or host specific. Through evolution the parasite has acquired the ability, which is essential for its survival, to assemble, amplify and transfer this genetic information in a viral form to another eucaryotic host. Prior results from this laboratory have shown that one family of the venom-related (VR) wasp and polydnavirus (PDV) genes belong to the "DEAD" protein family whose members are implicated in the control of gene expression at the levels of translation and splicing. This suggests that these unique genes may regulate splicing or translation of wasp and/or host genes. Recent studies show also that three CsPDV genes contain a cysteine motif characteristic of peptide toxins. The presence of this motif may reflect a function as a ligand of cell surface receptors which may correlate with parasite survival. Polydnavirus expression products and venom secretions may be more related in "host regulation" phenomena than previously thought.The next stage of this research will be directed toward identifying these expression products and determining their functional significance. The life cycles of certain wasps involve a stage at which they are parasites on other insects such as moths. The adult wasp lays its eggs by injecting them into the body of a larval moth. Special secretions are injected along with the eggs. These secretions contain factors that protect the eggs from the host's immune defense mechanisms and arrest the development of the host. In at least some such parasite/host relationships, a virus is an important component of this interaction. This laboratory is approaching this complex problem by identifying parasite and virus genes and gene products involved in this relationship. The overall goal of this research is to understand the molecular basis of the parasite-induced avoidance of host insect defense systems.