The amphioxus ERK2 gene is involved in innate immune response to LPS stimulation

The ERK2 gene is a member of the MAPK family, which plays very important roles in responses to external environmental pressures. However, the ERK2 has yet not been identified in amphioxus to date. To further illuminate the function and evolutionary mechanism of the ERK2 gene, in this present study, we have cloned the full length of the ERK2 gene of Branchiostoma belcheri (designed as AmphiERK2), which is highly homologous to these vertebrate ERK2 genes. The AmphiERK2 protein contains the conserved S_TKc domain and the TEY motif, and its 3D structure is also highly similar to human ERK2 protein. Taken together, our results indicate that the AmphiERK2 gene belongs to a member of the ERK2 gene family. We further use qRT-PCR technology to detect an ubiquitous expression of AmphiERK2 gene in all five investigated tissues (muscle, notochord, gill, hepatic caecum and intestine), and the expression level of AmphiERK2 in both notochord and muscle is significantly higher than the other three tissues. Meanwhile our results also demonstrate that LPS stimulation can induce the up-regulation expression of AmphiERK2 gene and significantly increase the phosphorylation level of AmphiERK2 protein, which seems to imply that the AmphiERK2 may be involved in amphioxus innate immune responses. Overall, our findings provide an important insight into amphioxus innate immune function and evolution of the ERK2 gene family.