REAf/f WAP-Cre mice display increased apoptosis of mammary epithelial cells. A, The cell cycle inhibitor p21 levels are elevated in the mammary gland of REAf/f WAP-Cre (WC) mice, as measured by qRT-PCR. The data are mean ± sd and are illustrated as relative expression normalized to 36B4 by wild-type P8. B, Representative fluorescence images of TUNEL staining in mammary gland sections from REAf/f and REAf/f WAP-Cre mammary glands of L14 mice. C, Immunohistochemical detection of active caspase-3 expression in the REAf/f and REAf/f WAP-Cre mammary glands of L14 mice. #, P < 0.05 vs. wild type.