Fig. 1. Dynamic expression of Sox2^EGFP in foregut-derived organs during mouse development. (A-C,M-P) Fluorescence microscopy of foregut organs from Sox2^EGFP/+ embryos. N is a cryosection of M. (D-F) Immunohistochemical localization of Sox2 protein in sections of foregut before and after separation into trachea and esophagus. Nuclei are counterstained with DAPI. (G-I) Immunohistochemical localization of p63. (J-L) Immunohistochemical localization of Nkx2.1. (Q-U) Sections through boundary (arrowhead) between stratified keratinized epithelium of the E18.5 forestomach and glandular epithelium of posterior stomach. Immunohistochemistry localizes Sox2 (Q), p63 (R), Keratin 14 (S) and involucrin (T) in keratinized epithelium whereas Periodic Acid Schifff (PAS) staining marks mucus-producing luminal cells of glandular stomach (U). Scale bars: 500 µm in A-C; 50 µm in all others. du, duodenum; es, esophagus; fg, foregut; lu, lung; st, stomach; tr, trachea.