ABSTRACT
Expression of functional differentiation of the mammary epithelial cells is accompanied by the appearance of several specific gene products, such as the caseins, α-lactalbumin, and the whey-acidic proteins. In murine mammary glands, prolactin and a glucocorticoid are the principal hormones required for lactogenesis. Mammary cells pre-exposed to steroid hormones can retain the same hormone for a prolonged period of time. Therefore, the possibility whether the significant accumulation of mRNAcsn in the mammary glands incubated first with cortisol and insulin, and then in medium containing prolactin and insulin was due to a synergistic action of residual steroid hormone with prolactin was determined. Progesterone acts as an inhibitor of lactogenesis. Thus, it was of interest to know whether the ovarian steroid hormone exerts its influence at the regulatory level of expression of the casein genes. Progesterone is known to compete for the cytoplasmic glucocorticoid receptors in mouse mammary cells.
