Morphogenesis of mouse mammary epithelial cells growing within collagen gels: ultrastructural and immunocytochemical characterization.

Mammary epithelial cells from adult virgin mice have been cultured within collagen gels in totally serum-free medium containing either epidermal growth factor or the mammogenic hormones, progesterone and prolactin, or prolactin alone. The cellular organization, differentiation and cell-type composition of the colonies from the three culture conditions were assessed by transmission electron microscopy and light-microscope immunocytochemistry. The epithelial cells form branching duct-like structures and, when exposed to mammogenic hormones, assume a secretory morphology (including casein micelles) similar to that seen in the early to mid-pregnant mouse.