Molecular And Functional Characterization Of Type Ⅰ And Type Ⅱ Interferons,and Retinoic Acid-inducible Gene Ⅰ(RIG-Ⅰ)-like Receptors In Snakehead Channa Argus

Two types of interferons(IFNs),i.e.type Ⅰ,type Ⅱ and type Ⅳ IFNs,are so far reported in teleost fish.Type Ⅰ IFNs in fish are currently divided into three groups,groups Ⅰ,Ⅱ and Ⅲ,and further into seven subgroups,including IFNa,IFNb,IFNc,IFNd,IFNe,IFNf,IFNh,and in fish,type Ⅱ IFNs contain two members,IFN-γ and IFN-γ related(IFN-yrel).In the present study,four type Ⅰ IFN(named as IFNc,IFNdl,IFNd2 and IFNh)and two type Ⅱ IFN(IFN-γ and IFN-γrel)genes were identified in the snakehead Channa argus,a perciform fish with aquacultural importance in some Asian countries,including China.The ORF of IFNc,IFNd1,IFNd2,IFNh,IFN-γ and IFN-γrel genes consists of 549,555,591,570,606 and 564 nucleotides(nt),predicted to encode 182,184,196,189,201 and 187 amino acids(aa)with theoretical molecular weight of 20.43,20.85,22.45,22.09,22.69 and 21.01,respectively.The type Ⅰ and type Ⅱ IFNs share 58.2-73.5%and 54.8-56.1%amino acid sequence identities with those respectively in mandarin fish,Siniperca chuatsi,also a perciform fish.It is found that the type Ⅰ and Ⅱ IFN genes are located at conserved loci when compared with other fish.These snakehead IFNs are expressed constitutively in also examined organs/tissues and are induced by polyinosinic and polycytidylic acid(poly(I:C)).In addition,four potential backbone groups of type Ⅰ IFNs,represented by IFNb,IFNc,IFNe and IFNf in ancient teleost fish,were discussed in this study based on the known evidence,which may provide new hypothesis to understand the evolution of type ⅠIFNs in teleost fish.Fish retinoic acid-inducible gene Ⅰ(RIG-Ⅰ)-like receptors(RLRs)are critical RNA sensors in cytoplasm and are involved in antiviral innate immunity.However,some species of fish lack RIG-I gene,and the function of RLR members in RIG-I-absent fish is poorly understood.In the present study,MDA5,LGP2 and MAVS genes were identified in commercially important snakehead Channa argus.But,RIG-I gene was not found in this fish,and a systematic analysis of RLRs in available genome database of fish indicated the absence of RIG-I in the Acanthomorphata,Clupeiformes and Polypteriformes,suggesting that loss events of RIG-I gene may have occurred independently three times in the evolutionary history of fish.The MDA5,LGP2 and MAVS in snakehead have conserved protein domains and genomic location based on sequence,phylogenetic and syntenic analyses.These genes are constitutively expressed in healthy fish and can be induced by poly(I:C)stimulation in vitro.It is further revealed that the snakehead MDA5 and LGP2 have binding capacity with dsRNA,such as poly(I:C),and MDA5 can interact with MAVS,implying the antiviral function of MDA5 in the RIG-I-absent fish.