Normal mammary epithelium in cortactin and cyclin D1 nulliparous, but not in multiparous transgenic mice. (A) Whole mounts of the abdominal mammary gland from nulliparous mice of wild type (WT), cortactin transgenic (T16), cyclin D1 transgenic (MP1) and cortactin/cyclin D1 bitransgenic (T16*MP1) mice at 20 weeks of age. The dark spot in the middle represents a lymph node. (B) Whole mounts of the abdominal mammary gland of post-weaned multiparous mice with mammary intraepithelial neoplasia (MIN) and hyperplastic alveolar nodules (HAN, arrows). The age in weeks and the number of pregnancies that the mouse went through, are indicated between brackets.