Molecular characterization and evolution analysis of five interleukin-17 receptor genes in large yellow croaker Larimichthys crocea.

Interleukin-17s (IL-17s) play critical roles in inflammatory response and host defense against extracellular pathogens. IL-17s induce the immune response signaling through the specific IL-17 receptors (IL-17Rs) that consist of five members (IL-17RA to E). In the present work, we have identified the five IL-17R orthologs (LycIL-17Rs) from large yellow croaker Larimichthys crocea. The deduced protein of each LycIL-17R exhibits a typical IL-17R domain architecture, including a signal peptide, the extracellular FNIII domain (IL-17RA/RB/RD) or IL-17_R_N domain (IL-17RC/RE), a transmembrane domain, and a SEFIR domain in cytoplasmic region. In particular, the extracellular regions of teleost IL-17RB are much shorter than those in mammals and lack an FNIII domain (FN2). Phylogenetic tree shows that IL-17Rs are classified into two main groups: IL-17RA/RB/RD group and IL-17RC/RE group, which is distinct from previous proposal that grouped IL-17RB into IL-17RC/RE. The surrounding genes of IL-17Rs are conservatively aligned in genomes between teleosts and mammals. The five LycIL-17Rs were constitutively expressed in all tissues examined, but with different expression patterns. Aeromonas hydrophila infection significantly upregulated LycIL-17RA, RC, RD and RE in both mucosal tissue (gills) and systemic immune tissues (head kidney and spleen), while the increase of LycIL-17RB expression could be detected in gills, indicating that LycIL-17Rs may be involved in host defense against bacterial infection. Thus, these results suggest that teleost IL-17Rs may function in mediating immune response as their mammalian orthologs. To our knowledge, this is the first report of molecular characterization of the five IL-17Rs (IL-17RA/RB/RD and IL-17RC/RE) in teleost fish.