MAYER, L.P* and; DYER, C. A.; PROPPER, C. R.: Sexual dimorphism in gonadal steroidogenic factor 1 (SF-1) expression during sexual differentiation and the effects of octylphenol on the differentiation process in the American bullfrog Rana catesbeiana.
Gonadal steroidogenesis during development is critical to differentiation of the adult sexually dimorphic phenotype and reproductive function. Environmental contaminants may play a role in affecting the process of sexual differentiation through disruption of steroidogenic action. Control of the steroidogenic pathway is regulated, in part, by P450 cytochrome hydroxylases, and the expression of many of these enzymes is controlled by the orphan nuclear receptor, steroidogenic factor-1 (SF-1). In mammals, SF-1 expression is critical for development of the reproductive axis and adult reproductive function. In Rana catesbeiana during sequential stages of development, we determined that SF-1 protein expression becomes elevated in ovaries of sexually differentiating females, while expression in testes decreases as differentiation occurs. Next, we exposed animals to the industrial pollutant, octylphenol (OP), for 24 hours before and during the critical stages of sexual differentiation. We found that animals treated with OP prior to the normal time of differentiation underwent early gonadal differentiation and those that differentiated into females had elevated SF-1 expression. This is the first study to investigate changes in SF-1 during development at the protein level. Our results suggest that 1) SF-1 expression differs between males and females during sexual differentiation in a pattern similar to chickens and alligators, but different from mammals and turtles, and 2) OP affects the timing of differentiation in bullfrogs demonstrating that OP has effects on developmental processes.