Expression and Transcript Localization of star, sf-1, and dax-1 in the Early Brain of the Orange-Spotted Grouper Epinephelus coioides

We investigated the developmental expression and localization of sf-1 and dax-1 transcripts in the brain of the juvenile orange-spotted grouper in response to steroidogenic enzyme gene at various developmental ages in relation to gonadal sex differentiation. The sf-1 transcripts were significantly higher from 110-dah (day after hatching) and gradually increased up to 150-dah. The dax-1 mRNA, on the other hand, showed a decreased expression during this period, in contrast to sf-1 expression. At the same time, the early brain had increased levels of steroidogenic gene (star). sf-1 and star hybridization signals were found to be increased in the ventromedial hypothalamus at 110-dah; however, dax-1 mRNA signals decreased in the early brain toward 150-dah. Furthermore, the exogenous estradiol upregulated star and sf-1 transcripts in the early brain of the grouper. These findings suggest that sf-1 and dax-1 may have an antagonistic expression pattern in the early brain during gonadal sex differentiation. Increased expression of steroidogenic gene together with sf-1 during gonadal differentiation strongly suggests that sf-1 may play an important role in the juvenile grouper brain steroidogenesis and brain development.