The conservation and uniqueness of the caspase family in the basal chordate, amphioxus

摘要

Background The caspase family, which plays a central role in apoptosis in metazoans, has undergone an expansion in amphioxus, increasing to 45 members through domain recombination and shuffling. Results In order to shed light on the conservation and uniqueness of this family in amphioxus, we cloned three representative caspase genes, designated as bbtCaspase-8, bbtCaspase-1/2 and bbtCaspase3 -like, from the amphioxus Branchiostoma belcheri tsingtauense . We found that bbtCaspase-8 with conserved protein architecture is involved in the Fas-associated death domain-Caspase-8 mediated pro-apoptotic extrinsic pathway, while bbtCaspase3 -like may mediate a nuclear apoptotic pathway in amphioxus. Also, bbtCaspase-1/2 can co-localize with bbtFADD2 in the nucleus, and be recruited to the cytoplasm by amphioxus apoptosis associated speck-like proteins containing a caspase recruitment domain, indicating that bbtCaspase-1/2 may serve as a switch between apoptosis and caspase-dependent innate immune response in invertebrates. Finally, amphioxus extrinsic apoptotic pathway related caspases played important roles in early embryogenesis. Conclusions Our study not only demonstrates the conservation of bbtCaspase-8 in apoptosis, but also reveals the unique features of several amphioxus caspases with novel domain architectures arose some 500 million years ago.