Differentiation and morphogenesis of mammary cells in vitro.

Cells of a mammary cell line isolated from a DMBA-induced rat mammary carcinoma undergo differentiation in vitro. A reversible differentiation leads to the formation of two types of microstructure (domes and ridges); this paper is concerned with the mechanism of dome formation. This differentiation is initiated by inducers, some of which are generated in the cultures and act locally; their effect is strongly dependent on cell concentration and requires hydrocortisone. There are, in addition, exogenous inducers as well as inhibitors. In the pathway to dome formation important roles are played by cAMP (probably both intracellular and extracellular), the organization of the cytoskeleton, and the Thy-1 antigen. The pathway and the significance of the phenomenon for mammary gland development are discussed.