Molecular characterization and expression analysis of tumor necrosis factor receptor-associated factors 3 and 6 in large yellow croaker (Larimichthys crocea).

The large yellow croaker (Larimichthys crocea) has a well-developed innate immune system. To gain a better understanding of the defense mechanisms involved in this system, we studied tumor necrosis factor receptor-associated factors (TRAFs), which play important roles in the Toll-like receptor (TLR) pathway. We characterized the full-length open reading frames and protein structures of TRAF3 and TRAF6 to determine their identities, and conducted phylogenetic analysis to determine their evolutionary relationships. To assess the roles of TRAFs in innate immune responses in the large yellow croaker, we performed quantitative reverse-transcription PCR (qRT-PCR) to characterize expression profiles in a range of tissues at different stages after challenge with polyinosinic polycytidylic acid (poly I:C) and Vibrio anguillarum. Following poly I:C challenge, the expression levels of TRAF3 and TRAF6 were highest in the kidneys and lowest in the spleen, whereas after infection with V. anguillarum, TRAF6 expression was the highest in the kidneys and lowest in the liver.