Secretion of casein in cultures of mouse mammary epithelial cells on floating collagen gels.

To study the effect of hormones on the secretion of casein, mammary epithelial cells were obtained from mid-pregnant mice and cultured on floating collagen gels in the presence of combinations of insulin, cortisol, and prolactin in serum-free culture medium. After labeling with phosphorus-32 labeled orthophosphate, the cells which had been cultured in the presence of all three hormones secreted hot-trichloroacetic acid precipitable radioactivity into the medium. The secreted materials were identified as three major mouse caseins by sodium dodecyl sulphate-urea polyacrylamide gel electrophoresis followed by autoradiography. The floating collagen gel culture method allows mouse mammary epithelial cells to differentiate and secrete all species of caseins in the presence of hormones. The present culture method and the phosphorus-32 labeling method will be applicable to the study of differentiation of mammary epithelial cells from a variety of mammalian species.