Identification and characterization of transforming growth factor β induced gene (TGFBIG) from Branchiostoma belcheri: insights into evolution of TGFBI family.

The transforming growth factor β induced gene (TGFBIG) encodes a protein (TGFBI) which plays important roles in many biological processes. However, no TGFBIG homolog has been reported in B. belcheri. Here, we identified a TGFBI-like gene from B. belcheri and extensively studied the evolutionary history of TGFBI family. We found that the amphioxus genome contains a TGFBIG homolog designated as AmphiTGFBI which encodes a protein with 5 Fas1 domains. The TGFBIGs were present in a common ancestor with Amphimedon queenslandica. We also demonstrated expression patterns of AmphiTGFBI in five amphioxus tissues. Interestingly, the gene structures and conserved motifs of invertebrate TGFBIGs were found to present regular changes in the evolution. Positive selection and Fas1 domain loss might cause the regular changes of gene structures and conserved motifs in invertebrate TGFBIGs during evolution. Together, our findings provided an insight into the evolution of the TGFBI family.