Mesenchymal-epithelial interactions in an in vitro model of neonatal mouse uterus.

Stromal factors have been implicated in epithelial growth of the fetal and neonatal mouse uterus, as well as in uterine epithelial proliferation in the adult. In the neonate, uterine growth is independent but responsive to estrogen, while epithelial proliferation in the adult uterus is hormonally regulated. A co-culture model was developed to study interactions between uterine epithelium and stroma. Uteri of neonatal mouse were enzymatically separated into epithelial and mesenchymal cell fractions, and these were cultured for 5 days on Millipore well inserts, either separately or in co-culture on opposite sides of the insert membrane. When epithelial cells were grown alone, inclusion of serum in the culture medium tripled the number of cells present after 3-5 days compared with serum-free medium. Co-culture in the presence or absence of serum resulted in a 5-fold increase in epithelial cell number after 5 days. Addition of estrogen had no significant effect on epithelial cell number regardless of the presence of mesenchyme. Epithelial cultures grown in medium conditioned by mesenchymal cells exhibited an intermediate increase in cell number. We therefore conclude that uterine mesenchyme from neonatal mouse produces a diffusible factor that enhances the growth of the overlying epithelium; however, whether the mesenchyme has a role in estrogen-stimulated epithelial proliferation has not been definitively ascertained.