Expression of the DMRT gene and its roles in early gonadal development of the Japanese pufferfish Takifugu rubripes

DMRT1, a gene containing the Doublesex/Mab-3 DNA-binding motif (DM domain), encodes a transcription factor that regulates early differentiation of Sertoli cells in the testes of vertebrates. Here, we describe the pattern of expression of six DMRT genes (DMRT1, 2a, 2b, 3, 4, and 5) during gonadal development in the Japanese pufferfish, Takifugu rubripes, for the first time. Conventional histological analysis showed that a primordial gonad is present 2 weeks after hatching and that sexual differentiation had occurred by 6 weeks after hatching, as determined by the formation of cavities in the ovaries. RT-PCR analysis showed that the DMRT1 transcript was abundant in the testes, but not in the ovaries, of 3-month-old fish. DMRT3 transcript was also detected in the testes, but not in the ovaries, indicating that the patterns of gonadal expression of DMRT3 are very similar to DMRT1. The other four DMRT genes examined did not exhibit sex-specific expression patterns. In situ hybridization analysis revealed that, after gonadal differentiation was complete, DMRT1 was expressed in the Sertoli cells that were in proximity to proliferating spermatogonia. These results indicate that DMRT1 involved in gonadal development rather than sex differentiation and that its expression correlates with the proliferation of spermatogonia in T. rubripes. The expression profile of DMRT1 in T. rubripes was similar to that in the teleost species Medaka.