Abstract
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.
Highlights
Steroid synthesis is a biochemical process that occurs in the nervous system as well as the classical peripheral steroidogenic organs, notably in the brain [1]
We have shown the developmental expression and localization of steroidogenic factors such as sf-1 and dax-1 transcripts in the early female brain of the orange-spotted grouper at different developmental ages in comparison to another key steroidogenic enzyme gene
In contrast to this scenario, lower expression of dax-1 was found in the early brain during gonadal sex differentiation when sf-1 and other key steroidogenic enzymes were high, indicating that the grouper brain has a functional peak of neurosteroidogenis that may be regulated by sf-1 and dax-1 (Figure 7)
Summary
Steroid synthesis is a biochemical process that occurs in the nervous system as well as the classical peripheral steroidogenic organs, notably in the brain [1]. These neurosteroids participate in a variety of physiological and behavioral processes during the early developmental period that are still unclear. The transcriptional regulation of neurosteroidogenic enzymes in the brain has been reported in a number of teleosts in relation to gonadal differentiation [2–7] and adult neurogenesis [8]. These findings provide evidence that neurosteroid production is under the control of brain steroidogenic enzymes. Characterization and molecular expression of star have been reported in different vertebrates during development, which includes chicken [10], rat and marmoset [11], and teleosts [2,12–15]
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