Characterization and expression analysis of the myeloid differentiation factor 88 (MyD88) in rock bream Oplegnathus fasciatus.

Myeloid differentiation factor 88 (MyD88) is a universal adaptor protein able to activate nuclear factor-kappa B (NF-κB) through interactions with interleukin-1 receptor (IL-1R) and the Toll-like receptors (TLRs), with the exception of TLR3. Here, we describe the identification of MyD88 from the rock bream fish Oplegnathus fasciatus and its characterization based on GS-FLX™ sequencing. The cDNA of rock bream MyD88 was found to be composed of 1626 bp, with an 867 bp open reading frame that encodes 288 amino acids. The deduced amino acid sequence of MyD88 possessed both a conserved death domain at the amino terminus and a typical Toll-IL-1 receptor (TIR) domain at the carboxyl terminus, similar to that found in other fishes, amphibians, avians, mammals and invertebrates. The mRNA expression pattern of MyD88 in healthy and bacterially challenged rock bream were examined using quantitative real-time polymerase chain reaction (qRT-PCR). MyD88 transcripts were found to be strongly expressed in blood, gill, liver, spleen, head kidney and kidney, moderately expressed in skin, brain and intestine, and weakly expressed in muscle. Expression levels of MyD88 in blood, spleen and head kidney were dramatically up-regulated upon exposure to LPS and the Gram-negative bacteria Edwardsiella tarda, suggesting that MyD88 plays an important role in rock bream defenses against bacterial infection.