Advances in aquatic animal RIG-I-like receptors

Abstract

Retinoic acid-inducible gene I (RIG-I)-like receptors (RLRs) sense microbial-associated molecular patterns (MAMPs) to activate the innate immune responses. RLRs in aquatic animals include RIG-I, MDA5, LGP2, mollusc RIG-I-like and MDA5-like proteins, which exhibit structural and functional diversity. RLRs data from 30 species of aquatic animals were collected for analysis. Not all species contain all the RLR members. RIG-I is absent in the orders of Perciformes, Cichliformes and Pleuronectiformes, and LGP2-like protein is absent in the class of Bivalvia. Due to the differences in species and variants, the homologous proteins have different responses to pathogens. LGP2 works as an immune homeostasis regulator to balance the immune response. The phylogenetic analysis demonstrates RIG-I and mollusc RIG-I-like present in the same evolutionary branch and appear in the early stage. RIG-I is an ancient PRR in innate antiviral immunity. The prototype of antiviral immune system has emerged in aquatic mollusc. Aquatic animal RLRs were analyzed and summarized in terms of structures, functions, and evolutions, which provide the basic information for future researches in RLRs. Base on the diversity of species and RLRs, more and in-depth studies in aquatic animal RLRs should be done.