Generation of viperin-knockout zebrafish by CRISPR/Cas9-mediated genome engineering and the effect of this mutation under VHSV infection.

Viperin is an important virus-induced protein in animals that negatively participates in RNA viral replication and transcription. The reactive machinery of viperin suggests that it produces a regulatory molecule ddhCTP, which may affect immune regulation. In this study, we investigated the expression pattern of viperin in larval and adult stages of zebrafish by whole-mount in situ hybridization and reverse transcription-quantitative PCR (RT-qPCR). To elucidate the function of viperin, we generated a zebrafish knockout model using the CRISPR/Cas9 method and evaluated the mutation's effects under viral hemorrhagic septicemia virus (VHSV) infections. In zebrafish larvae, viperin was expressed in the brain region, eye, and pharynx, which was confirmed by cryosectioning. In adult zebrafish, blood cells showed the highest levels of viperin expression. In 5 dpf fish challenged with VHSV, the expression of the viral NP protein was significantly enhanced in viperin-/- compared to wild-type fish. In vitro VHSV propagation analysis indicated comparatively higher levels of virus propagation in viperin-/- fish. Mortality analysis confirmed higher mortality rates, and interferon gene expression analysis showed a strong upregulation of interferon (ifn)φ1 and 3 gene in viperin-/- fish infected with VHSV. This study describes the successful generation of a viperin-knockout model and the role of viperin during VHSV infections.