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Fish Rhabdoviruses are responsible for causing fatal epizootics within commercial and wild populations of various fish species around the world. Infectious hematopoietic necrosis virus (IHNV), also known as the Salmonid novirhabdovirus, is enzootic along the Pacific Coast of North America and is comprised of five genogroups, each of which is endemic to a specific geographical location. Once the virus enters the host through the fin epithelia, IHNV infection causes infectious hematopoietic necrosis in salmonid species. The disease is highly fatal and presents with signs such as abdominal distension, bulging of the eyes, anemia, and necrosis of vital organs such as the liver and kidneys, all caused by systemic hemorrhaging within the host.
The 11-kb negative-sense, ssRNA viral genome within IHNV consists of six genes that encode the nucleoprotein (N), phosphoprotein (P), matrix protein (M), glycoprotein (G), nonvirion protein (NV), and RNA-dependent RNA polymerase (L), in order from 3’ to 5’, respectively (Fig. 1). While most of the protein products from the IHNV genome have been studied and elucidated, the precise function of the NV protein remains unknown. While multiple studies have reported various roles for NV, such as suppression of apoptosis, interferon (IFN) induction, and NF-κB activation, data from our lab suggest that NV augments transcriptional or translational responses in the host. Using transient transfections and luciferase reporter assays, we have observed upregulation of host cell transcription/translation and innate immune responses. Regardless of the proposed functions of NV, functional sites within the viral protein are poorly defined. With the introduction of C- and N-terminal deletion mutations (∆NV), we were able to characterize the effects of mutated NV on rainbow trout gill epithelial cell (RT-Gill) constitutive and induced transcriptional responses using specific luciferase reporter plasmids, pCAGluc and RT-IFNluc. Our results suggest that while all ∆NV mutants showed a decrease in the augmented luciferase expression obtained with WT-NV, mutations within the N-terminal region of the protein led to an inhibitory effect on constitutive or induced luciferase expression. These data suggest that the N-terminal region of NV plays a critical role in the upregulation of host cell expression.
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Ringiesn , J., Gorgoglione , B., & Leaman , D. W. (2020). Functional Sites within the IHNV NonVirion Protein that Regulate Host Cellular Responses. .
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