| Research Abstract |
The C3 and C6 genes were isolated from a cephalochordate, amphioxus, establishing the presence of the complement system in cephalochordates. The presence of C6 containing the MAC/perforin domain strongly suggests that the invertebrate complement system is equipped with the cytolytic mechanism, whereas only opsonic activity has been demonstrated thus far. From a urochordate, Halocynthia roretzi, the MASP, C3, Bf and CR3 alpha genes and proteins were identified. In addition, through the annotation of the draft genome sequence of another ascidian species, Ciona intestinalis, many possible complement component genes, including C1q and many cytolytic components were identified, indicating that the complement system was well developed in the last common ancestor of urochordates and vertebrates.
The evolution of the MHC gene organization was analyzed using a bony fish medaka and a cartilaginous fish shark. The C4 and Bf genes were linked to the MHC class I and II genes in shark. Since sharks are most primitive animal to possess the MHC, this result suggests that the class III complement genes were original members of the MHC.
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