Myeloid differentiation factor 88(MyD88) is a universal adaptor protein involved in Toll-like receptors and in interleukin-1 receptor-induced nuclear factor-kappaB(NF-κB) activation.In this study,a new MyD88 gene(designated as Og-MyD88) was cloned from orange-spotted grouper,Epinephelus coioides,based on the expressed sequence tag(EST) obtained following Roche 454 GS-FLX sequencing.The full-length Og-MyD88 cDNA is composed of 1682 bp and encodes a deduced polypeptide of 289 amino acids with 86% homology to MyD88 of Siniperca chuatsi.The deduced amino acid sequence of Og-MyD88 contains a typical death domain at the amino terminus and a conserved Toll/IL-1R(TIR) domain at the carboxyl terminus,as well as three highly conserved motifs(Box1,Box2 and Box3) within the C-terminal TIR domain.In healthy fish,Og-MyD88 was found to be strongly expressed in immune-related tissues,including the spleen,head kidney,kidney,liver,skin and intestine,with lower expression in heart,stomach,brain and muscle.Transcripts of Og-MyD88 were found to be markedly up-regulated in fish spleen after challenge with Singapore grouper iridovirus(SGIV),a highly lethal viral pathogen to grouper fish.Furthermore,the full length Og-MyD88 and its N-terminal death domain were capable of inducing NF-κB activity in HEK-293 cells.Overexpressed Og-MyD88 showed the ability to inhibit replication of SGIV in grouper spleen(GS) cells.These results suggest that Og-MyD88 is involved in the grouper immune response to invasion of viral pathogens and may share similar functions to those observed in higher vertebrates.
YAN YangCUI HuaChunWEI JingGuangHUANG YouHuaHUANG XiaoHongQIN QiWei
