Figure 2.

Paracrine induction of side-branching by Wnt-1. Primary mammary epithelial cells were derived from 10-week-old MMTV Wnt-1^tg and ROSA26 females. After 5 days in vitro culture, the cells were trypsinized, mixed in a 1:1 ratio, and injected into cleared fat pads of 3-week-old RAG1^−/− recipients. Mammary glands from RAG1^−/− recipients at 10 weeks after surgery were subjected to X-gal stain, carmine alum counterstain, and mounted whole. (Top) Cleared fat pad reconstituted with a mixture of ROSA26 (blue) and MMTV Wnt1 (red) mammary epithelial cells; (bottom) ungrafted control, thoracic mammary gland. Bar, 500 μm. Wnt-1 overexpressing cells (red) induce premature side-branching in wild-type cells (blue).