Molecular characterization and functional analysis of MyD88 in Chinese soft-shelled turtle Trionyx sinensis

Myeloid differentiation factor 88 (MyD88) is one of the key adaptor proteins to signal transduction that triggers downstream cascades involved in innate immunity. In this study, the MyD88 gene from Chinese soft-shelled turtle (Trionyx sinensis) (tMyD88) was identified, representing the fist example from reptile species. The tMyD88 has a 894-bp ORF and encodes a polypeptide of 297 amino acids including a typical death domain (DD) at the N-terminus and a conservative Toll/IL-1R (TIR) domain at the C-terminus. It was expressed at high levels in spleen, blood, lungs and liver, but marginal in kidneys and intestines of turtles challenged with live cells of Aeromonas hydrophila, as determined by real-time PCR. RAW 264.7 cells transfected with pcDNA-tMyD88 showed higher NF-κB activity than the vector control (673.78 vs 410.72, P < 0.05). Expression of proinflammatory cytokines IL-1β and TNF-α was also significantly higher in RAW 264.7 cells transfected with pcDNA-tMyD88 than those having pcDNA3.1 control vector (P < 0.01). These results indicate that tMyD88 might possess an important role in defense against microbial infection in Chinese soft-shelled turtles similar to that in mammals.