Fig. 2. Expression of N57-ß-catenin in basal mammary cells induces precocious development in pregnancy, persistent proliferation in lactation and accelerated involution. (A) Precocious lobuloalveolar development in pregnant K5-N57-ßcat mice. Wholemount staining of mammary glands from pregnant wild-type (WT) and transgenic mice. (B) Premature secretory cell differentiation in pregnant K5-N57-ßcat mice. ß-Casein expression in 7.5-day-pregnant mouse mammary glands. Alveoli from K5-N57-ßcat mice contain more ß-casein than those from wild-type littermates. Immunostaining with anti-ß-casein (green) and anti--SM-actin (red) antibodies. (C) Persistent proliferation in K5-N57-ßcat mouse mammary glands at peak lactation. Staining with anti-BrdU antibodies (upper panel) and TUNEL assay (lower panel). The number of BrdU-positive cells (arrows) is greater in lactating transgenic mouse mammary glands after 6 days of lactation than in wild-type animals, whereas apoptosis rates are not altered. (D) Accelerated involution in K5-N57-ßcat mammary glands as revealed by Hematoxylin and Eosin staining (HE, top panel) and TUNEL assay (bottom panel). Sections through 3-day-old involuting mammary glands. P7.5, P10.5 and P13.5 correspond to 7.5, 10.5 and 13.5 days of pregnancy; L6, to 6 days of lactation; I3, to 3 days of involution. Scale bars: 4 and 0.5 mm in A; 20 µm in B; 100 µm in C; 200 µm in D (upper panel), 100 µm in D (lower panel).