Hormonal control of milk protein synthesis in cultured mouse mammary explants

SDS-urea polyacrylamide gel electrophoresis of mouse milk proteins revealed the presence of three major phosphoproteins (caseins) of m.w. 44,000, 26,000 and 22,000 daltons. By using an antiserum against crude casein fraction, an immunoprecipitation method was developed for the quantitative measurement of the rate of milk protein synthesis in the mouse mammary tissue. Cultivation of mammary explants with insulin, cortisol and prolactin resulted in the induction of milk protein synthesis as evidenced by the incorporation of [3H]amino acid and [32P]orthophosphate into immune precipitable materials. The present immunoprecipitation method coupled with a simplified explant culture technique provides a suitable procedure for the study of mouse mammary gland differentiation.