Hormone Inducible Specific Gene Expression in an Isolated Whole Mammary Organ in Serum-Free Culture

Selective gene expression is believed to play a critical role in cellular differentiation associated with developmental processes (1). Functional differentiation (lactogenesis) of the mammary epithelial cells is accompanied by hormone-inducible expression of several specific gene products including the major milk-proteins, the casein (2). In the murine mammary gland, a glucocorticoid (Cortisol or corticosterone) and prolactin are the principal steroid and polypeptide hormones required for lactogenesis including the synthesis of the caseins, a phosphoprotein complex (3,4). Progesterone is also involved in this process and is known to act as a suppressor of lactogenesis (5). This chapter includes a brief discussion of our recent findings on the mode of action of the different steroid and polypeptide hormones involved in the regulation of the expression of the casein genes in an isolated whole mammary organ in vitro. Earlier studies on milk-protein gene expression in the mammary gland in vivo and in vitro have been reviewed in recent years (6–10).