Differentiation of vaginal epithelium in mice given estrogen and thymidine‐H³

Adult mice of the A/Jax strain were given injections of thymidine‐H 3 at proestrus and injections of estrogen at one day intervals thereafter, up to eight days. Mice were killed at daily intervals and longitudinal sections of vagina were radioautographed. Cells which were immediately above the basal layer at proestrus, and which would have given rise to the mucous, nucleated cell layer, eventually produced an interruption in the otherwise continuous cornification of the surface layers. A similar experiment, begun at late metestrus, produced comparable results, except that the interruption of cornification was more pronounced. Mice which had been ovariectomized two weeks previously were given injections of estradiol and thymidine‐H 3 . Cells at the surface continued to show a low frequency of mitotic activity and retained their nuclei after estradiol treatment. They were finally sloughed by the squamous transformation of underlying cells. The latter were derived originally from the basal layer under the influence of estradiol, which led to greatly accelerated mitotic activity in that layer. It is concluded that the course of cellular differentiation in these migrating cells is fixed when they are produced by mitosis of basal cells. This differentiation can only be modified, not reversed, by subsequent estradiol treatment even when the cells involved are still capable of undergoing mitosis.