Apoptosis in the estrous and menstrual cycles

In the absence of pregnancy, the adult mammary gland is subjected to cyclic fluctuations of hormonal stimulation that constitute the estrous and menst rual cycles. The mammary epithelium responds to these systemic hormonal cha nges by regional proliferation, differentiation and cell death by apoptosis . The fact that the mammary epithelial response involves only a minor subse t of the epithelial cells implies a delicate local control of epithelial ce ll fate resulting in either cell death or survival. Evidence gleaned from d escriptive data suggests that the apoptosis-related genes of the Bcl-2 gene family, tissue remodeling genes, protein tyrosine kinases and master genes of the homeotic gene cluster may be involved in determining epithelial cel l fate during the estrous cycle.