Role of steroidogenic factor I and aromatase in temperature-dependent sex determination in the red-eared slider turtle

Red-eared slider turtles are genetically bipotential for sex determination. In this species, as in many other reptiles, incubation temperature of the egg determines gonadal sex. At higher incubation temperatures females are p roduced and increasing temperature appears to increase estrogen production in the embryonic brain. Treatment of eggs incubating at a male-producing te mperature with exogenous estrogen causes ovaries to form. At a female-biase d incubation temperature, prevention of estrogen biosynthesis or administra tion of nonaromatizable androgens results in the development of testes. In mammals, steroidogenic factor 1 (SF-1) regulates most genes required for es trogen biosynthesis, including aromatase. In both mammals and red-eared sli ders, SF-1 is differentially expressed in males and females during gonadoge nesis. We have examined both SF-1 gene expression and aromatase activity in embryos incubating at different temperatures and after manipulation to cha nge the course of gonadal development. Our findings indicate a central role for SF-1 in enacting the effect of estrogen. Estrogen treatment directly o r indirectly downregulates SF-1 and, ultimately, causes development of fema les. The inhibition of estrogen results in upregulation of SF-1 and male ha tchlings. Thus, SF-1 may lie at the center of one molecular crossroad in ma le versus female differentiation of the red-eared slider. J. Exp. Zool. 290 :597-606, 2001. (C) 2001 Wiley-Liss, Inc.