Responses to double stranded RNA in oysters: developing a model for antiviral immunity

The aquaculture industry faces challenges and major economic losses from infectious disease outbreaks of farmed stocks. Ostreid herpes virus type 1 (OsHV-1 μvar) infection of larval and juvenile Pacific oysters is a worldwide phenomenon. This thesis investigates responses to exogenous double stranded RNA (dsRNA) in two oyster species that are farmed extensively in Australia - the Pacific oyster (Crassostrea gigas) and Sydney rock oyster (Saccostrea glomerata). dsRNAs are products of viral infection and in many biological systems, dsRNA provokes strong immune responses. While C. gigas is susceptible to viral infection, S. glomerata appears to be resistant. This study examines molecular basis for the differential susceptibility to OsHV-1 infection using state-of-the-art mass spectrometry (iTRAQ and SWATH) proteomics, transcriptomics and fluorescence microscopy techniques. This is the first comparative study of the immune systems of two oyster species that behave differently to OsHV-1 and also provides the proteome map of the Sydney rock and the Pacific oysters. Both oyster species were capable of detecting exogenous dsRNA, but differed in the patterns of double stranded RNA uptake and processing, as well as in their proteomic responses to that perturbation. Gill tissues are an important site of dsRNA processing and response. In response to dsRNA, Sydney rock oysters activated cellular signalling pathways, as well as apoptotic (cell death) pathways, that are typical of antiviral responses in metazoans. These responses were absent in the Pacific oysters. The data provides a useful model for further studies into resistance to viral infection in these oysters, as well as unravelling the molecular mechanisms that underpin the biological differences in viral susceptibility.