Changes in ontogenetic expression of estrogen receptor alpha and not of estrogen receptor beta in the female rat reproductive tract.

To evaluate ontogenetic expression and localization of estrogen receptor (ER) alpha and beta in fetal female rat reproductive tract, competitive RT-PCR and immunohistochemistry were performed. Expression levels for Müllerian ERalpha, ERbeta1 and ERbeta2 mRNAs were determined by competitive RT-PCR. ERalpha expression on gestational day (GD) 15 x 5 increased 4 x 4-fold by GD 21 x 5, whereas both ERbeta1 and ERbeta2 gene expression were maintained at lower constant levels compared with ERalpha during development. ER immunolocalization was evaluated within three regions along the Müllerian duct axis; these were proximal, middle and caudal, which differentiate into oviduct, uterus and upper vagina respectively. Nuclear ERalpha was localized predominantly in proximal Müllerian epithelium, and middle and caudal Müllerian mesenchyme on GDs 15 x 5-21 x 5. Staining intensity for ERalpha increased with development in all regions. However, ERbeta immunoreactivity was not detected in any region during prenatal life after separate staining with three different polyclonal anti-rat ERbeta antibodies. These findings provide fundamental information critical for clarifying the species-specific physiological roles of ER subtypes during fetal development and for investigating the tissue-specific mechanisms underlying the prenatal response to estrogen and estrogen receptor agonists.