FIG.4.

Stat5 is required for functional differentiation of the mammary epithelium. Inguinal mammary glands were collected from Stat5^fl/fl (A, C, E, and G) and Stat5^fl/fl/WC (B, D, F, H, I, and J) mice at lactation. (A and B) H&E staining showed sparser alveoli in Stat5^fl/fl/WC mammary gland at lactation than in the Stat5^fl/fl littermate. (C to J) Mammary tissues were harvested at parturition and stained with antibodies that characterize the differentiation state of epithelial cells. Uniform nuclear Stat5 (red) staining was seen in the Stat5^fl/fl gland (C). However, a conspicuous nonuniform staining of Stat5 was observed in most alveoli in Stat5^fl/fl/WC tissue (D) (arrowhead). NKCC1 (red) expression was undetectable in Stat5^fl/fl/WC and Stat5^fl/fl epithelia during lactation (E and F) (arrow); smooth muscle actin (green) stained the myoepithelial cells. Alveoli in Stat5^fl/fl/WC displayed heterogeneous Npt2b staining (red) at parturition (H) (arrow). While this marker for secretory activity was seen on the apical membrane in expanded alveoli, it was absent in alveoli with a small lumen (G and H) (arrowhead). E-cadherin (green) was used to stain the cell membrane. (I and J) Serial sections from a Stat5^fl/fl/WC gland stained with Stat5 (red) (I) and WAP (red) (J); E-cadherin (green) was applied in both sections. Note that cells without Stat5a (I) (arrows) do not express WAP at parturition (J) (arrows). Bars, 250 μm (A and B) and 50 μm (C to J).