Thesis

Identification and characterization of differentially expressed genes in white spot virus infected Penaeus stylirostris

White Spot Syndrome Virus (WSSV), a dsDNA virus, is the most important viral pathogen in cultured penaeid shrimp worldwide. In cultured shrimp, WSSV infection can reach a cumulative mortality of up to 100% within 3-10 days upon infection. Intensive shrimp cultivation, inadequate sanitation, and worldwide trade have aggravated the disease dissemination. As such, WSSV has become an epizootic disease and is not only a major threat to shrimp culture but also to marine ecology. In recent years, considerable progress has been made in characterizing the WSSV at the molecular level and developing highly sensitive methods for WSSV detection. However, information pertaining to shrimp cellular genes that are involved in WSSVhost interaction is very limited. To address this issue, this research project took an expressed sequence tags (ESTs) approach to isolate and characterize randomly selected eDNA clones from a hepatopancreas eDNA library ofWSSV-infected shrimp, in order to isolate genes that might play a role in WSSV pathogenesis. The expression of immune/receptor genes, lectin (PsEST 640) and a low-density lipoprotein receptor (PsEST 160) were identified by EST analysis, were measured by RT-PCR. Real-time quantitative (RT-PCR) using SYBR Green chemistry has been shown to be a rapid and highly sensitive detection method for shrimp viruses as well as to measure cellular gene expression in shrimp. A statistically significant difference was observed in the expression of lectin at 32 h p.i. with upregulation in healthy compared to that ofWSSV-infected. LDLr, a receptor known to interact with viruses, had increased expression in the WSSV-infected individuals at 4 h p.i. compared to the healthy. Our data suggests that lectin is a highly diverse, inducible protein that may play a direct/indirect role in either binding WSSV and/or initiating some humoral defense mechanism (i.e. prophenoloxidase cascade). In addition, LDLr gene was found to play a role in shrimp-WSSV interaction, and possibly be a receptor to which the virus binds.

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