Mx of Sebastes schlegelii: expression pattern, antibacterial activity and antiviral mechanism

Myxovirus resistance (Mx) is a classical antiviral molecule that has been well understood in mammals. However, very limited studies on Mx antiviral activities have been documented in teleosts. In the present study, a novel Mx (SsMx) was cloned from black rockfish (Sebastes schlegelii) and the immunological activities of SsMx were examined in vitro and in vivo. SsMx contained conserved structural and functional domains including GTPase domain and GTPase effector domain. Quantitative real-time PCR (qRT-PCR) revealed that SsMx is extensively distributed in the immune cells and tissues examined with higher levels in spleen and liver. The mRNA expression of SsMx was significantly upregulated in head kidney, spleen and head kidney macrophages after pathogen infection. Recombinant SsMx (rSsMx) exhibited apparent binding activities against different bacteria in vitro. In vivo studies showed that rSsMx reduced pathogen dissemination and replication in head kidney and spleen. The subcellular localization results demonstrated that SsMx was predominantly distributed in the cytoplasm of transfected cells. Furthermore, SsMx was observed to inhibit apoptosis in virus-infected cells and reduce viral replication by interfering with the viral entry. SsMx and Spring viremia of carp virus Glycoprotein (SVCV G) were found to interact strongly with each other by co-immunoprecipitation and co-localization. These findings reveal an important role of SsMx in defencing the early stage of SVCV infection, which will be helpful to understand the molecular details of the antiviral mechanisms mediated by Mx proteins in teleosts.