Fish specific duplication of Dmrt2: characterization of zebrafish Dmrt2b

The protein families with a conserved zinc finger-like DNA binding DM domain are putative transcription factors related to the sexual regulator Dsx of Drosophila and Mab-3 of Caenorhabditis elegans. Although several members have been cloned, there are still other members need to be identified, and origin and evolution of the gene family also remain unclear. We report here cloning, expression and synteny analysis of a duplicated copy of zebrafish Dmrt2a gene, the Dmrt2b which is fish specific, whereas Dmrt2a exists in all vertebrates. During embryogenesis, the Dmrt2b expression increased gradually from shield stage to hatching stage, and mainly localized in branchial arches from 24 hpf to 40 hpf, indicating that it has a potential role in the development of branchial arches. The duplicated Dmrt2b and Dmrt2a with structural variation and expression diversification during development revealed that a process of functional diploidization of gene function occurred during zebrafish lineage. DNA binding experiment indicated that Dmrt2b recognized similar DNA sequences to those of both DSX and MAB-3, indicating a conserved regulatory function. Synteny analysis among chromosomes containing Dmrt2a and Dmrt2b showed that zebrafish Dmrt2b and at least nine genes on chromosome 6 have respective homologues on chromosome 5 containing Dmrt2a. Further synteny search from genome information showed that Dmrt2b and its neighborhood existed only in the genome of teleosts. Dmrt2a and Dmrt2b were duplicated from the duplication event, which might be part of the third genome duplication, occurred during the evolution of ray-finned fishes, probably before the emergence of osteichthyes around 350 Myr. The duplicated Dmrt2b and Dmrt2a with structural variation and expression diversification suggested their diverse roles: Dmrt2b in specification of branchial arches while Dmrt2a in somitogenesis. These analyses undoubtedly help understanding functional divergence and evolution of the DM genes following gene duplication in fishes.