Fig. 4. Modeling mammary acinar structure in 3D organotypic co-cultures. Purified primary human luminal epithelial cells were embedded and cultured in lrBM (A) or collagen I gels (B,C) in the absence (A,B) or presence (C) of purified myoepithelial cells (MEP). Cultures were double stained for the lumenal marker, sialomucin (red) and the basolateral marker, epithelial-specific antigen (ESA; green). Luminal epithelial cells form polarized organotypic spheres in lrBM but adopt inverse polarity in collagen I gels. Addition of purified myoepithelial cells to luminal epithelial cells in collagen I corrects acinar polarity (C) and results in formation of a bilayered organotypic structure. Reproduced with permission from Gudjonsson et al. (Gudjonsson et al., 2002a).