Mammary gland hyperplasia in MMTV βTrcp1 transgenic mice. (A) Whole mounts (a, b, d, and e) and hematoxylin and eosin-stained sections (c and f) of inguinal mammary glands from 10-week-old virgin MMTV βTrcp1 transgenic mice (d to f) and wild-type (WT) littermates (a to c). LN, lymph node. (g) BrdU incorporation in breast epithelium of 10-week-old virgin WT and estrus-matched MMTV βTrcp1 transgenic littermates. The percentages of BrdU-positive nuclei were calculated. (h) Percentages of TUNEL-positive nuclei at different days after removal of pups. Error bars represent standard errors of the means. (B) Whole mounts (a, b, d, and e) and hematoxylin and eosin-stained (c and f) sections of inguinal mammary glands from 22-month-old WT mice (a to c) and MMTV βTrcp1 transgenic littermates (d to f).