D. Crews et al., Role of steroidogenic factor I and aromatase in temperature-dependent sex determination in the red-eared slider turtle, J EXP ZOOL, 290(6), 2001, pp. 597-606
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.