ER-α expression in reconstituted mammary glands. Epithelial mammary cells of BALB/c or C57BL/6 mice were purified and implanted into cleared fat pads of untreated nu/nu mice (as explained in Materials and methods). After 1 month, mammary glands were excised and fixed for histological evaluation. (a) ER-α was evaluated using MC 20 Santa Cruz antibody and PR-A (not shown) using C-20 Santa Cruz antibody (bar: 45 μm). (b) The number of stained cells is expressed as the percentage of stained cells among epithelial cells in 400× fields of every slide. ER, estrogen receptor; PR, progesterone receptor.