Identification and characterization of a TAB1 gene involved in innate immunity of amphioxus (Branchiostoma belcheri).

Transforming growth factor-β activated kinase-1 (TAK1) is an essential regulator in toll-like receptor (TLR), tumor necrosis factor (TNF) and interleukin-1 (IL-1) signaling pathways, and plays very important roles in animal innate immunity. TAK1-binding protein, TAB1, can specifically regulate the activation of TAK1. However, the TAB1 gene in amphioxus has not yet been identified to date. In this study, we identified and characterized a TAB1 gene from Branchiostoma belcheri (designed as AmphiTAB1). Our results showed that the full-length cDNA of AmphiTAB1 is 2281bp long with an open reading frame (ORF) of 1659bp that encodes a predicted protein of 553 amino acids containing a typical PP2Cc domain. Phylogenetic analysis indicated that the AmphiTAB1 gene was located between invertebrates and vertebrates, suggesting that the AmphiTAB1 gene is a member of the TAB1 gene family. Real-time PCR analysis indicated that the AmphiTAB1 was ubiquitously and differentially expressed in six investigated tissues (gills, hepatic cecum, intestine, muscles, notochord and gonad). After lipopolysaccharide stimulation, the expression of AmphiTAB1 was significantly up-regulated at 6h, which shows that AmphiTAB1 may be involved in the host immune response. In addition, the recombinant TAB1 expressed in vitro shows a molecular mass of 62kDa and Western blot confirmed it, which proved it is an encoding isoform. Taken together, our findings provide an insight into innate immune response of amphioxus and evolution of the TAB1 gene family.