Bovine mammary myoepithelial cells. 2. Interactions with epithelial cells in vitro.

The objective of this study was to examine interactions of bovine myoepithelial and epithelial cells in vitro. Mammary tissue was dissociated with collagenase into myoepithelial and epithelial cells. Myoepithelial and epithelial cells were separated by differential centrifugation. Both cell types were cultured on plastic in RPMI-1640 and Iscove's Modified Dulbecco's Modified Eagle Medium supplemented with 10% horse serum and 5% fetal bovine serum. Our data revealed that conditioned medium from epithelial cells caused a small but significant reduction in proliferation of myoepithelial cells from fetal mammary glands. Myoepithelial-epithelial cell interaction in culture was characterized by myoepithelial cells with extended filopodia that could grow on top of confluent monolayers of epithelial cells, imitating the in vivo situation. In confluent monolayers of epithelial and myoepithelial cells in coculture, small domelike structures consisting of mixtures of epithelial and myoepithelial cells were observed. These structures greatly resembled the in vivo organization of the bovine mammary gland. Furthermore, myoepithelial cells were capable of migration toward individual colonies of epithelial cells or single epithelial cells. Myoepithelial cells organized epithelial cells into well-defined colonies. Myoepithelial cells may play an important role in organizing the architectural framework of the mammary gland during growth and development.