Expression and promoter analysis of Xenopus DMRT1 and functional characterization of the transactivation property of its protein.

The doublesex and mab-3-related transcription factor 1 (DMRT1) is involved in testis formation in a variety of vertebrates. In the teleost fish, Medaka, DMY/DMRT1Y on the Y chromosome, a duplicate of the autosomal DMRT1 gene, is characterized as a sex-determining gene. We report here the characterization of the Xenopus DMRT1 genes. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that X. laevis DMRT1 was expressed throughout the embryo during early development and was restricted to the primordial gonads after embryogenesis. Whole-mount in situ hybridization analysis of the gene confirmed its specific expression in the primordial gonads. To study the transcriptional control of DMRT1 gene expression, we isolated the predicted promoter region of X. tropicalis DMRT1 using databases for this species. Analysis of transgenic tadpoles with a green fluorescence protein (GFP) reporter showed that approximately 3 kb of the 5'-flanking sequence of the DMRT1 gene was implicated in DMRT1 expression in the primordial gonads. We also showed that the C-terminal region of DMRT1 functioned as a transactivation domain in cultured cells, by a luciferase reporter assay using fusion proteins with the DNA-binding domain of GAL4. These findings suggest that DMRT1 functions as an activator of one or more genes involved in sex determination or gonadal differentiation.