The complement system of elasmobranches revealed by liver transcriptome analysis of a hammerhead shark, Sphyrna zygaena.

Comprehensive studies of the complement genes in basal vertebrates have revealed that cyclostomes have apparently primitive complement systems whereas bony fish have well-developed complement systems comparable to those of mammals. Here we have performed liver transcriptome analysis of a hammerhead shark, Sphyrna zygaeana, to elucidate the early history of vertebrate complement evolution. Identified genes were; one C1qB, one C1r, one C1s, one MASP-1/-3, one MASP-2, two factor B/C2, one C3, three C4, one C5, one C6, one C7, one C8A, three C8B, one C8G, one C9, two factor I and one S protein. No MBL, ficolin, C1qA or C1qC were found. These results indicate that the lectin, classical, alternative and lytic pathways were established in the common ancestor of jawed vertebrates. In addition to the absence of MBL and ficolin, the MASP transcripts lacked the serine protease domain, suggesting that the lectin pathway was lost in the hammerhead shark lineage.