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 polyinosinic and polycytidylic acid (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.

鱼维甲酸诱导基因 I (RIG-I) 样受体 (RLR) 是细胞质中的关键 RNA 传感器，参与抗病毒先天免疫。然而，一些鱼类缺乏RIG-I基因，RLR成员在缺乏RIG-I的鱼类中的功能知之甚少。在本研究中，MDA5、LGP2 和 MAVS 基因在商业上重要的蛇头Channa argus中被鉴定出来。. 但是，在这条鱼中没有发现 RIG-I 基因，对现有的鱼类基因组数据库中的 RLRs 进行系统分析表明，棘形目、鲱形目和多翅目中不存在 RIG-I，这表明 RIG-I 基因的丢失事件可能在鱼类的进化史上独立发生过 3 次。根据序列、系统发育和同线分析，蛇头中的 MDA5、LGP2 和 MAVS 具有保守的蛋白质结构域和基因组位置。这些基因在健康鱼类中组成型表达，并且可以通过体外多聚肌苷和多聚胞苷酸 (poly(I:C)) 刺激来诱导. 进一步揭示了蛇头MDA5和LGP2与dsRNA如poly(I:C)具有结合能力，MDA5可以与MAVS相互作用，表明MDA5在RIG-I缺失的鱼中具有抗病毒作用。