Developmental changes of the oestrogen receptor-alpha and -beta mRNAs in the female reproductive organ of the rat--an analysis by in situ hybridization.

This study employed an in situ hybridization technique to compare the cellular expression of oestrogen receptor (ER) subtypes, ER alpha and beta, in the female reproductive organ of the rat during prenatal and postnatal periods. Diffuse signals of ER alpha and beta mRNAs were co-expressed in the foetal ovary; they were weak and inconsistent before onset of gonadal differentiation, but increased in intensity with age. ER beta mRNA signals in the ovary sharply increased in intensity to adult levels by postnatal days 6-7, whereas those of ER alpha mRNA remained unchanged after birth. ER alpha was the sole subtype expressed during the prenatal period from the oviduct to the vagina, being localized mainly to the sub-epithelial stromal cells, and remained predominant thereafter. Signals for ER alpha mRNA in the epithelia were confined to the oviduct during prenatal and early postnatal periods; those in uterine and vaginal epithelia first appeared by postnatal days 4-5 and 6 respectively. Expressions of ER beta mRNA in the reproductive tract were absent during the prenatal period, and were weakly expressed during the postnatal period. Thus, oestrogen action in the developing ovary may be co-mediated by both ER alpha and beta, whereas ER alpha may be the primary mediator in the differentiation and growth of the female reproductive tract.