Fig. 6. ß-catenin overexpression at the earliest stage of transdifferentiation. (A) Western blot showing expression of K14, ß-catenin and E-cadherin in mammary abscesses (lanes 1-5) and adjacent normal gland (lane 6). (B) All abscesses examined, irrespective of their sizes (arrows), are positive for ß-catenin as demonstrated by this section from a 1-year-old Smad4^Co/CoWAP-Cre mouse. (C-R) Analyzing squamous metaplasia at three distinct phases as described in the text: phase I (C-F, and arrowhead in G-J); phase II (arrow in G-J); and phase III (K-R). C,G are amplified from Fig. 3C,E, respectively. Antibodies used are as indicated. Arrows in C indicate undifferentiated alveolar structures. The arrow and arrowhead in G indicate the differentiated and undifferentiated alveolar structures, respectively. Notice that cells prior to differentiation (arrowhead) express only ß-catenin but not K-14, while the differentiating cells (arrow) express both. The arrow in K indicates a small, but well formed abscess that expresses both genes. The arrows in O indicate initiating metaplasia, which express K14 at high levels but E-cadherin at significantly lower levels. Scale bars: 140 µm in K-N; 70 µm in B-J,O-R.