Estrogen receptors α and β in the rodent mammary gland

摘要

An obligatory role for estrogen in growth, development, and functions of the mammary gland is well established, but the roles of the two estrogen receptors remain unclear. With the use of specific antibodies. it was found that both estrogen receptors, ERα and ERβ. are expressed in the rat mammary gland but the presence and cellular distribution of the two receptors are distinct. In prepubertal rats, ERα was detected in 40/100 of the epithelial cell nuclei. This decreased to 30/100 at puberty and continued to decrease throughout pregnancy to a low of 5/100 at day 14. During lactation there was a large induction of ERα with up to 70/100 of the nuclei positive at day 21. Approximately 60-70/100 of epithelial cells expressed ERβ at all stages of breast development. Cells coex- pressing ERα and ERβ were rare during pregnancy, a proliferative phase. but they represented up to 60/100 of the epithelial cells during lactation, a postproliferative phase. Western blot anal- ysis and sucrose gradient centrifugation confirmed this pattern of expression. During pregnancy, the proliferating cell nuclear antigen was not expressed in ERα-positive cells but was ob- served in 3-7/100 of ERβ-containing cells. Because more than 90/100 of ERβ-bearing cells do not proliferate. and 55-70/100 of the dividing cells have neither ERα nor ERβ, it is clear that the presence of these receptors in epithelial cells is not a prerequi- site for estrogen-mediated proliferation.