The DMRT gene family in amphioxus.

Doublesex and Mab-3-related transcription factor (DMRT) gene family is widely known for its involvement in sex determination and/or differentiation among different phyla. In this study, we identify eight DMRT genes in the cephalochordate amphioxus, a protochordate holding a key phylogenetic position. The eight DMRTs can be divided into two groups based on the conserved domain: BfDM044, BfDM045, BfDM55.1, BfDM115.1, and BfDM17.1 belong to the first group which have both DM and DMA domains, while BfDM246.1, BfDM084, and BfDM175 belong to the second group which have only DM domain. Most of the first group members have same genomic structure except BfDM17.1, while no regular pattern exists in the second group. Phylogenetic analysis of the DM domain sequences shows that DMRT genes in vertebrates form seven different independent clusters, and some even contain genes from invertebrates with high bootstrap. Notably, the first group members of amphioxus cluster with vertebrate DMRTs; while the second group members cluster into a single branch, which diverge from the vertebrate classes. The results suggest that several DMRT genes in vertebrates may evolve from homologous genes in invertebrates. As in nematode, drosophila, fish, and vertebrates, DMRT genes cluster is also found in amphioxus, which may be the result of gene duplication. Interspecific differences in the amphioxus DMRTs and sea squirt DMRTs may suggest post-speciation duplication of some DMRT genes.