Figure 4.

Estradiol suppression of Cyp17a1 expression is mediated by ERα. Shown is quantitative data (average ± SEM) from real-time RT-PCR for Cyp17a1 and Cyp11a1 transcripts in wild type day 5 follicles following 24 h of treatment with either vehicle (Veh), an aromatase inhibitor (AI), an ER-antagonist (ICI); or an AI plus estradiol (E₂), an ERα-agonist (PPT) or an ERβ-agonist (DPN). As expected, acute withdrawal of endogenous estradiol synthesis (via an AI) or direct repression of ER action (via ICI) leads to increased Cyp17a1 expression (top). However, this can be prevented by co-treatment with exogenous E₂ or an ERα-specific agonist (PPT), indicating that ERα mediates the estradiol suppression of Cyp17a1 expression in growing follicles. In contrast, Cyp11a1 expression (bottom) was not affected by the various treatments, indicating the effects of ERα-mediated estradiol are specific to Cyp17a1. Bars that do not share a letter are significantly different (P < 0.05). The data shown is one of two independent experiments that yielded comparable results. Sample sizes were 8–9 follicles per genotype, per treatment, per experiment.