E-cad⁻ cells were excluded from polarized ducts and the body cell compartment of the TEB in vivo. (A) Adeno-Cre–transduced mT/mG organoids (E-cad⁺) were transplanted into cleared mammary fat pads, and glands were harvested after 6 wk. (B and C) Both TEBs (B) and polarized ducts (C) contained a mixture of red and green cells in the luminal and myoepithelial cell layers. (D) Adeno-Cre–transduced E-cad^fl/fl;mT/mG organoids were transplanted into contralateral no. 4 glands. (E) E-cad⁻ luminal cells were markedly excluded from the body cell region of the TEB in ductal outgrowths. Arrowheads indicate green cells in the cap cell layer. (F and G) E-cad⁻ luminal cells were observed on the basal surfaces of polarized epithelium in the gland periphery (F) and near the injection site (G). (H) E-cad⁻ cells were also observed in disorganized clusters surrounded by myoepithelial cells (H’, SMA⁺). (I) Cre-ER;E-cad^fl/fl;mT/mG organoids (E-cad⁺) were transplanted into cleared mammary fat pads and allowed to grow out for 6 wk. Tamoxifen was injected to induce E-cad deletion, and glands were harvested after 2–6 wk. (J) E-cad⁻ cells were observed in the lumens (J’) and on the basal surfaces (J’’) of E-cad⁺ polarized ducts (nine glands). Bars, 10 µm.