Phylogenetically conserved TAK1 participates in Branchiostoma belcheri innate immune response to LPS stimulus

Transforming growth factor-β activated kinase-1 (TAK1) is an important member of the mitogen-activated protein kinase kinase kinase (MAP3K) family, which plays an important role in animal innate immune response. However, the TAK1 gene has yet not been reported in amphioxus to date. Here, we have identified and characterized a TAK1 gene from amphioxus (Branchiostoma belcheri) (named as AmphiTAK1) with the full-length cDNA of 3479 bp, including an ORF sequence of 1905 bp, a 5' UTR of 394 bp and a 3' UTR of 1180 bp. Moreover, the predicted AmphiTAK1 protein contains STKc_TAK1 domain, TAB1 and TAB2/3 binding domain which are conserved among chordate, and phylogenetic analysis also shows that the AmphiTAK1 is located at the bottom of the chordate, revealing AmphiTAK1 as a new member of the TAK1 gene family. The further qRT-PCR analysis has shown that AmphiTAK1 is widely expressed in six investigated tissues (gonad, gill, hepatic cecum, intestine, muscle and notochord) of Branchiostoma belcheri, with high expression in notochord and gonad, moderate in gill and hepatic cecum. Notably, the expression level of AmphiTAK1 is significantly up-regulated after LPS stimulation. Specially, we also find that AmphiTAK1 protein can interact with AmphiTAB1 by immunoprecipitation assay. These findings reveal that AmphiTAK1 might interact with AmphiTAB1 to involve in innate immune response of Branchiostoma belcheri. Taken together, our present works provide a new insight into evolution and innate immune response mechanism of AmphiTAK1 gene in Branchiostoma belcheri.