Claudin multigene family in channel catfish and their expression profiles in response to bacterial infection and hypoxia as revealed by meta-analysis of RNA-Seq datasets.

Claudins are one of the major groups of transmembrane proteins that play crucial roles in tight junctions. In addition to their function in the regulation of paracellular permeability, claudins are also involved in a number of biological processes related to pathogen infection, embryonic development, organ development and hypoxia response. Despite its importance, analyses of claudin genes in channel catfish have not been systematically performed. In this study, a total of 52 claudin genes were identified and characterized in channel catfish. Phylogenetic analyses were conducted to determine their identities and identify a number of lineage-specific claudin gene duplications in channel catfish. Expression profiles of catfish claudin genes in response to enteric septicemia of catfish (ESC) disease and hypoxia stress were determined by analyzing existing RNA-Seq datasets. Claudin genes were significantly down-regulated in the intestine at 3h post-infection, indicating that pathogens may disrupt the mucosal barrier by suppressing the expression of claudin genes. A total of six claudin genes were significantly regulated in the gill after hypoxia stress. Among them, the expressions of cldn-11b and cldn-10d were dramatically altered when comparing hypoxia tolerant fish with intolerant fish, though their specific roles involved in response to hypoxia stress remained unknown.