Fig. 2. (A) Luminal cells make inside-out acini in collagen. Luminal cells were double-stained either for (a) sialomucin (red) and ESA (green); (b) sialomucin (red) and occludin (green); (c) nuclear stain (red) and ß4-integrin (green); or (d) nuclear stain (red) and type IV collagen (green). Spheres in collagen-I gel (a',b') exhibit reversed polarity compared with cells in rBM (a,b), do not target ß4-integrin basolaterally (compare c and c') and fail to deposit a basement membrane (compare d and d'). (B) Reversal of inside-out acini by addition of myoepithelial cells. In the presence of myoepithelial cells (a''-d''), the polarity is corrected as is the endogenous BM deposition and integrin targeting. (bar, 25 µm).