Figure 1.

Side-branching in the presence of Wnt-1 and absence of the PR. (A) Intrinsic side-branching defect in PR^−/− mammary epithelium. Mammary epithelium was harvested from PR^−/− ROSA26 (top) and PR^+/+ ROSA26 (bottom) 10-week-old female mice and engrafted to the cleared fat pads of 3-week-old F₁ (129SV/C57B16) recipients. Shown are whole-mount preparations of mammary glands subjected to X-gal stain, from a recipient at day 12 of pregnancy (10 weeks after surgery). Results were similar to those reported previously. Bar, 400, μm. (B) Constitutive side-branching of MMTV Wnt-1^tg irrespective of the PR status. Mammary epithelium was harvested from PR^−/− MMTV Wnt-1^tgand PR^+/+ MMTV Wnt-1^tb 10-week-old female mice and engrafted to the cleared fat pads of 3-week-old recipients. Shown are whole-mount preparations of mammary gland from a virgin RAG1^−/− recipient 10 weeks after surgery. (Left) Inguinal fat pad engrafted with PR^−/− MMTV Wnt-1^tg mammary epithelium; (right) inguinal fat pad engrafted with PR^+/+ MMTV Wnt-1^tg mammary epithelium; (center) thoracic mammary gland, as an ungrafted endogenous control. Identical results were obtained in 16 independent grafts of PR^−/− MMTV Wnt-1^tg and control mammary epithelium. Bar, 5 mm.