ESTROGEN RECEPTOR-BETA MESSENGER-RIBONUCLEIC-ACID ONTOGENY IN THE PROSTATE OF NORMAL AND NEONATALLY ESTROGENIZED RATS

Neonatal exposure to estrogens permanently alters rat prostate growth and epithelial differentiation leading to prostatic dysplasia on aging . The effects are lobe-specific, with the greatest response observed i n the ventral lobe. Recently, a novel estrogen receptor (ER) complemen tary DNA was cloned from the rat prostate and termed ER-beta (ER beta) due to its high homology with the classical ER alpha. The protein pos sesses high affinity for 17 beta-estradiol, indicating that ER beta is an alternate molecule for mediating estrogenic effects. Importantly, ER beta messenger RNA (mRNA) was localized to rat prostatic epithelial cells, which contrasts with the stromal localization of ER alpha in t he rat prostate. The present study was undertaken to determine the ont ogeny of ER beta mRNA expression in the rat prostate lobes and to exam ine the effects of early estrogen exposure on prostatic ER beta expres sion. Male rat pups were given 25 mu g estradiol or oil on days 1, 3, and 5; were killed on day 1, 3 (oils only), 6, 10, 30, or 90; and pros tate lobes were frozen. Longitudinal sections were processed for in si tu hybridization using an S-36-labeled antisense mRNA probe correspond ing to a 400-bp EcoRI-AccI fragment in the 5'untranslated region of ra t ER beta complementary DNA. Image analysis was used to quantitate sil ver grains. In addition, total RNA was isolated from the ventral prost ate (VP) and used for semiquantitative RT-PCR. Results from in situ hy bridization revealed that at birth, ER beta was equivalently expressed at low levels in both mesenchymal and epithelial cells in oil-treated rats. From day 1 onwards, expression in all stromal cells slowly and significantly declined, so that in the control adult prostate, stromal ER beta mRNA was slightly above background. In the oil-treated contro l rats, epithelial ERP mRNA increased to moderate levels between days 6-10 in the VP and days 10-15 in the dorsal and lateral lobes as cells began differentiation and ducts lumenized. A further significant incr ease in ER beta message was observed at day 30, which indicates that f ull epithelial ER beta expression may require the completion of functi onal differentiation. By day 90, expression levels were maximal and si milar between the lobes. RT-PCR substantiated this developmental incre ase in ER beta between days 1-90. Neonatal exposure to estrogens did n ot have an immediate effect on prostatic ER beta mRNA levels as determ ined by in situ hybridization and RT-PCR. However, the marked increase in epithelial cell expression at day 30 observed in the control VP wa s dampened in the VP of animals exposed neonatally to estrogens. By da y 90, the VP of estrogenized rats possessed low ER beta message levels compared with the high expression in oil controls. In contrast, the d orsal and lateral lobes of neonatally estrogenized rats possessed high levels of ER beta mRNA at day 90, equivalent to controls. The present data demonstrate that ER beta mRNA expression in the rat prostate is developmentally regulated, and that neonatal estrogen can affect this expression in the adult VP. Because the effect of neonatal estrogens w as not immediate, the data imply that early estrogen exposure may not directly autoregulate ER beta expression, and suggests that the adult effects on ER beta mRNA expression may be indirect. The differences in ER beta mRNA imprinting in the separate lobes may account for or refl ect the lobe-specific neonatal estrogen imprints previously observed i n the rat prostate.