Molecular cloning and characterization of DMRT genes from the medaka Oryzias latipes and the platyfish Xiphophorus maculatus

The DMRT genes constitute a family of genes, which possess a common motif called the DM domain. DMRT1 is considered to be involved in sex determination and/or sex differentiation, but not much information exists about the function of the other gene family members. We cloned DMRT genes of two important model fish species, the medaka, Oryzias latipes, and the platyfish, Xiphophorus maculatus. Based on sequence similarity and genomic structure with known DMRT genes, the gene from the medaka was identified as OlaDMRT4, and those from the platyfish as XmaDMRT2 and XmaDMRT4. OlaDMRT4 was assigned to the linkage group 18 (LG18) of the medaka by linkage analysis and fluorescence in situ hybridization. The earlier cloned medaka DMRT1, 2 and 3 genes form a cluster on LG9. Therefore, OlaDMRT4 does not belong to the DMRT gene cluster. In adult medaka fish, OlaDMRT4 is expressed in the brain, eyes, gill, kidney, as well as testis and ovary. During development, OlaDMRT4 exists as maternal transcripts, and is expressed until early larval stages. This pattern of expression differs from the other known medaka DMRT genes. Surprisingly it is also not the same as its putative tilapia ortholog ( DMO). These differences in expression suggest that DMRT4 might fulfill divergent functions in different species.