Simultaneous production of casein and mammary tumor virus in mouse mammary epithelial cells grown on floating collagen gels.

Simultaneous production of casein and mammary tumor virus (MTV) was analyzed in monolayer cultures of mammary epithelial cells from pregnant BALB/cfC3H mice. A comparison of the 2 cell culture substrata, plastic culture dish and floating collagen gel, showed that the latter supported a much higher degree of simultaneous casein and MTV production in the presence of insulin, cortisol and prolactin in serum-free culture medium. Importance of floating collagen gel was further shown by delaying the flotation of gels. When the release of gels was delayed, there were concomitant delays in the increase of casein and MTV production. These results indicate that hormones, nature of substratum and flotation regulate the degree of differentiation of mammary epithelial cells in vitro.