Figure 1. An expanded columnar epithelium consisting of basal and luminal cells at the esophageal squamous-columnar junction (SCJ) in Krt5-CreER;R26^Sox2-GFP mutants.

a, SOX2 overexpression leads to the formation of multilayered epithelium (MLE, dotted line) with basal (p63⁺, arrowheads) and luminal cells (KRT8⁺). n=7 per group. b, Basal progenitors at the SCJ generate the MLE (KRT7⁺GFP⁺SOX2^hi). n=7. c, Basal cells in the MLE express KRT5 (white line) but not Claudin18 which labels the cardia mucosa (yellow line). n=7. d, The MLE is located between the stratified squamous epithelium and the simple columnar cardia. Note two distinct basal progenitors at the SCJ. Sq, stratified squamous; Co, columnar. Scale bar, 20μm.