Identification and characterization of a p38-like gene from amphioxus (Branchiostoma belcheri): an insight into amphioxus innate immunity and evolution.

p38 MAP kinases, members of mitogen-activated protein kinases (MAPKs) activated by environmental stresses and cytokines, play important roles in transcription regulation and inflammatory responses. However, the p38 MAP kinase gene has not been identified in amphioxus to date. Here, we identified and characterized a p38 MAP kinase gene from Branchiostoma belcheri (designed as Amphip38). First, we cloned the full length of Amphip38 gene and found that the deduced amino acid sequence of Amphip38 has 80.5-84% similarity and 67.2-72.5% identity to those from other species. Second, we found that Amphip38 contained the conserved TGY motif, ATP binding site (GXGXXG), substrate binding site (ATRW) and ED site in known p38 MAP kinases. The predicted 3D structure of Amphip38 was found to be similar to human p38 MAP kinases. These results indicate that Amphip38 belongs to p38 MAP kinase gene family. Third, we found that the Amphip38 was ubiquitously and differentially expressed in five investigated tissues (intestine, gills, notochord, muscles, and hepatic cecum). Finally, we found that LPS stimulation induced the expression of Amphip38 gene, and lead to increase of phosphorylation-p38 MAP kinase. These results indicate that Amphip38 is involved in innate immunity response in amphioxus. In addition, we found that Amphip38 gene might be an ancestor of vertebrate p38 MAP kinase gene via evolutionary analysis. In conclusion, our results provided an insight into the innate immunity response and the evolution of the vertebrate p38 MAP kinase gene family.