Fig. 5. ß-catenin responsiveness is restricted to a subset of PR-negative mouse mammary cells, despite transgene expression in all cells. (A) Double immunofluorescence analysis of transgene detected by 9E10 (green) and PR expression detected by anti-PR (red) antibodies in a virgin MMTV-N89ß-catenin gland. (B) Expression of conductin-lacZ detected by X-Gal staining (blue, arrowheads) indicates that only a subset of ductal cells show a transcriptional response to uniform transgene expression immunohistochemically detected by 9E10 (brown) in a section of a PR^+/+;conductin^+/lacZ;N89ß-catenin gland. (C) PR immunohistochemistry on X-Gal-stained sections of PR^+/+;conductin^+/lacZ;N89ß-catenin glands demonstrates distinct populations of ß-catenin-responsive and PR-expressing cells. (D) Carmine and X-Gal-stained wholemount of a PR^+/+;conductin^+/lacZ;N89ß-catenin gland showing conductin-lacZ expression at sites of alveolar development. (E) Indirect immunofluorescence for detection of PCNA (green) and PR (red) reveals that proliferating cells are segregated from PR-expressing cells. (F) Immunohistochemistry for Ki67 on PR^+/+;conductin^+/lacZ;N89ß-catenin gland showing proliferation of one third of conductin-lacZ-expressing cells (arrows). Adjacent cells that do not express conductin-lacZ also proliferate. (G) Graphical representation of the percentage of Ki67-positive cells within PR-positive, conductin-lacZ-positive and conductin-lacZ-negative populations. Scale bars: 50 µm in A-C,E,F; 0.3 mm in D.