ONTOGENY OF ESTROGEN-RECEPTOR MESSENGER-RIBONUCLEIC-ACID EXPRESSION IN THE POSTNATAL RAT UTERUS

During the first 2 wk of postnatal life, the rodent uterus undergoes a period of marked growth and differentiation. To further examine the r ole of the estrogen receptor (ER) in the mediation of uterine developm ent, we analyzed the ontogeny of ER mRNA expression in the postnatal r at uterus using in situ hybridization. ER mRNA was present in the uter ine stroma on the day of birth and progressively increased in abundanc e during the first 2 wk of postnatal life. In contrast, ER mRNA was no t detectable in the luminal epithelium at birth and did not become abu ndant in this region until postnatal day (P) 7. ER mRNA abundance incr eased in the luminal epithelium and in the invaginating and fully form ed glandular epithelium during the second week of life. At P21 ER mRNA was more abundant in the glandular epithelium than in any other uteri ne cell type. These results are consistent with, and extend the findin gs of, previous studies using uterine homogenate binding assays and im munohistochemistry to define ER ontogeny in rodents. Delineation of th e temporal and cell-type specific pattern of ER mRNA ontogeny in the p ostnatal rat uterus furthers our understanding of the molecular basis of both endogenous and exogenous estrogen effects on uterine growth an d development.