Characterization and immune response expression of the Rig-I-like receptor mda5 in common carp Cyprinus carpio

In this study, the full‐length complementary (c)DNA of common carp Cyprinus carpio melanoma differentiation‐associated gene 5 (mda5) was cloned. The complete open reading frame of C. carpio mda5 contained 2982 bp and encodes 993 amino acids. The deduced amino acids contained six functional domains: two caspase activation and recruitment domains (CARD), a conserved restriction domain of bacterial type III restriction enzyme (ResIII), a DExD/H box‐containing domain (DEXDc), a helicase super family C‐terminal domain (HELICc) and a C‐terminal regulatory domain (RD). The mda5 gene was expressed in all tested tissues, with high levels in the gills and spleen, while lower expressed in gonad and blood. The copy numbers of mda5 were increased in the liver, spleen, head kidney and the mucosal‐associated immune tissues such as the foregut, hindgut, gills and skin after stimulation with polyinosinic polycytidylic [poly(I:C)] and Aeromonas hydrophila. The myxovirus resistance gene (mx) messenger (m)RNA levels in the spleen, head kidney, foregut and gills were significantly up‐regulated after poly(I:C) injection. When injected with poly(I:C), mda5 and mx transcripts were also significantly induced in vitro. These results implied that mda5 might be involved in both antiviral and antibacterial innate immune processes in C. carpio. © 2016 The Authors. Journal of Fish Biology © 2016 The Fisheries Society of the British Isles