Independent duplications of Bf and C3 complement genes in the zebrafish

As part of an ongoing project aimed at the characterization of the MHC syst em in bony fishes, we have attempted to identify the class III region in th e zebrafish (a teleost), a region that in higher vertebrates contains genes coding for complement proteins C2, Bf and C4, We obtained several genomic PAC clones by hybridization with a zebrafish Bf probe, previously identifie d in our laboratory, and searched these for the presence of other class III genes. We were able to obtain a second Bf-like gene, however, we were unab le to detect any C2- or C4-like genes. By using highly degenerated primers, we extended our search to a hepatopancreas cDNA library and amplified from it clones corresponding to three different C3-like genes, and also the Bf genes, but not any C2- or C4-like genes. The zebrafish therefore contains t wo Bf and three C3 loci but apparently no C2 and C4 loci. Independent dupli cations of the Bf and C3 genes in bony fishes suggest that complement plays a prominent part in the immune response of this class of vertebrates.