Secretion of Casein in Cultures of Mouse Mammary Epithelial Cells on Floating Collagen Gels

Abstract

To study the effect of hormones on the secretion of casein, mammary epithelial cells were obtained from mid-pregnancy 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 32P labeled orthophosphate, the cells which had been cultured in the presence of all 3 hormones secreted hot-trichloroacetic acid precipitable radioactivity into the medium. The secreted materials were identified as 3 major mouse caseins by sodium dodecyl sulfate-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 32P labeling method will be applicable to the study of differentiation of mammary epithelial cells from a variety of mammalian species.