Samples were harvested with trypsin after formation of the primary epithelium (described in Figures 4 and 5) and harvested again after the initial organotypic culture for the second organotypic culture. (A) There were only a few scattered epithelial cells in serial samples prepared form the organotypic cultures of unsorted WT (GFP^–) cells (H&E staining). (B–F) Immunohistochemistry revealed that the cells were GFP^– (B), Ki67^– (C), CK14^– (D), CK4^– (E), and CK13^– (F). (G) Only a few isolated clusters of epithelial cells did not form an epithelium from 10³ NSP cells from GFP⁺ mice mixed with 3 × 10⁴ unsorted GFP^– cells (H&E staining). (H–L) Immunohistochemistry revealed that the cells were mostly GFP^– (H), Ki67^– (I), minimally and irregularly CK14⁺ (J) and CK4⁺ (K), and CK13⁺ (L). (M) A complete epithelium formed, derived from sorted 10³ SP cells from GFP⁺ mice mixed with 3 × 10⁴ unsorted GFP^– cells (H&E staining). (N–R) Immunohistochemistry revealed that cells were GFP⁺ (N), basal cells were Ki67⁺ (O) and CK14⁺ (P), and suprabasal cells were CK4⁺ (Q) and CK13⁺ (R). Dashed line represents basement membrane. Original magnification, ×100 (insets in A, G, and M); ×400 (B–F, H–L, and N–R). Scale bars: 25 μm.