Identification and functional characterization of viperin of amphioxus Branchiostoma japonicum: Implications for ancient origin of viperin-mediated antiviral response

• Amphioxus viperin (BjVip) is shown to possess features in common with those of vertebrate viperin.
• N-terminal region of BjVip was detected evolving under positive selection.
• Bjvip exhibits a tissue-specific expression, and poly I:C induces enhanced expression of Bjvip.
• BjVip is capable of promoting resistance against viral infection in vitro and in vivo.
• Viperin-mediated antiviral response already emerged in the primitive chordate.

Viperin, an antiviral protein, has been shown to be active against a wide range of DNA and RNA viruses, but no information is available regarding functional characterization of viperin in invertebrate species. In this study, we clearly demonstrate that amphioxus (Branchiostoma japonicum) viperin, BjVip, has features in common with those of vertebrate viperin, including the presence of the SAM superfamily domain with the characteristic CNYKCGFC motif, syntenic conservation, and predicted 3D structure. Bjvip exhibits a tissue-specific expression with abundant levels in the hepatic cecum, hind-gut, gill and muscle, and following challenge with the viral mimic poly I:C, its expression is significantly up-regulated, suggesting an involvement of BjVip in immune response of amphioxus against viral infection. Importantly, we show that the cells transfected with Bjvip is able to kill LCDV or inhibiting its propagation, and co-incubation of rBjVip with WSSV markedly attenuates its infectivity. Thus, we provide the first evidences that amphioxus viperin, like that of vertebrates, is capable of promoting resistance against viral infection in vitro and in vivo, indicating that viperin-mediated antiviral response already emerged in the primitive chordate. We also prove that amphioxus viperin has evolved under positive selection.