FIG.5.

Stat5 is required for survival of the differentiated mammary epithelium. (A to D) Inguinal mammary glands were collected from Stat5^fl/fl (A and C) and Stat5^fl/fl/WC (B and D) mice at p15.5. (E and F) Mammary tissues harvested at p18.5. (A and B) Immunofluorescence staining of Cre recombinase (red) and E-cadherin (green) showed a mosaic pattern of WAP-Cre expression in p15.5 Stat5^fl/fl/WC mammary tissue (B) (arrows), and no WAP-Cre was detected in Stat5^fl/fl mice (A). (C and D) Uniform Stat5a (red) expression was observed in Stat5^fl/fl epithelium at p15.5, while about one-half of the epithelial cells had lost Stat5a expression in Stat5^fl/fl/WC mice (D) (arrowheads). E-cadherin (green) was used to stain cell membranes. (E and F) At p18.5 only a few mammary epithelial cells in Stat5^fl/fl/WC mice were negative for Stat5a (F) (arrowheads). E-cadherin was stained as green. (G) TUNEL assays were performed with the inguinal mammary glands at p15.5 and p18.5 from three Stat5^fl/fl and six Stat5^fl/fl/WC mice. At p15.5, 5.29% ± 2.07% (mean ± SEM) TUNEL-positive cells were observed in Stat5^fl/fl/WC epithelium, compared with 1.02% ± 1.0% in Stat5^fl/fl tissue. The difference was highly significant (P = 0.0046 by the two-tailed Student t test). In contrast, at p18.5 the number of apoptotic cells decreased to 1.03% ± 0.64% in the Stat5^fl/fl/WC mammary gland, which was comparable to the percentage of positive cells (0.97% ± 0.27%) in Stat5^fl/fl mice (P = 0.798).