Receptor tyrosine kinases (RTKs) are high-affinity
cell surface receptors for many
polypeptide growth factors,
cytokines and
hormones. RTKs are not only key regulators of normal cellular processes, but are also involved in the progression of many types of
tumors, and responses to various biotic and abiotic stresses. Catfish is a primary aquaculture species in the United States, while its industry is drastically hindered by several major diseases including enteric
septicemia of catfish (ESC) that is caused by Edwardsiella ictaluri. Disease outbreaks are often accompanied by hypoxic stress, which affects the performance and survival of fish by reducing
disease resistance. In this study, we identified 26 RTK oncogenes in the channel catfish genome, and determined their expression profiles after ESC
infection and hypoxic stress. The 26 RTK genes were divided into four subfamilies according to phylogenetic analysis, including TIE (2 genes), ErbB (6 genes), EPH (14 genes), and INSR (4 genes). All identified RTKs possess a similar molecular architecture including
ligand-binding domains, a single transmembrane helix and a cytoplasmic region, which suggests that these genes could play conserved biological roles. The expression analysis revealed that eight RTKs were significantly regulated after
bacterial infection, with dramatic induction of
insulin receptor genes including INSRb, IGF1Ra, and IGF1Rb. Upon hypoxic stress, EPHB3a, EGFR, ErbB4b, and IGF1Rb were expressed at higher levels in the tolerant catfish, while EPHA2a, EPHA2, TIE1 and INSRa were expressed at higher levels in the intolerant catfish. These results suggested the involvement of RTKs in immune responses and hypoxic tolerance.