Identification and characterization of IL-1 receptor-associated kinase-4 (IRAK-4) in half-smooth tongue sole Cynoglossus semilaevis.

As a crucial component in TLR/IL-1R signaling pathways, IRAK-4 plays a central role in innate and adaptive immunity. In the present study, the cDNA of IRAK-4 was cloned for the first time from half-smooth tongue sole (Cynoglossus semilaevis). The full-length cDNA of csIRAK-4 was 2149 bp and contained a 168 bp 5' UTR, a 580 bp 3' UTR and a 1401 bp CDS. The predicted protein sequence of csIRAK-4 had two typical domains, a death domain (DD) at the N terminus and a serine/threonine/tyrosine protein kinase domain (STYKc) at the C terminus. RT-PCR showed that csIRAK-4 mRNA was detected in all tested tissues, especially in immune-related organs, gonads and brain. After injected with inactivated Vibrio anguillarum, the expressions of csIRAK-4 were up-regulated significantly (P<0.05) in spleen and head kidney. During development, csIRAK-4 was expressed at all selected stages and low-level expression was detected at metamorphosis. Taken together, the present study indicated that csIRAK-4 played a crucial role in immune responses and might be involved in the process of development.