Fig. 4. Independent confirmation of the adverse effects of unregulated Wnt signaling in developing stomach endoderm. Findings in E18.5 Shh^Cre/+;Catnb^+/lox(ex3) mouse embryos. (A,B) Constitutive ß-catenin activation is confirmed by its nuclear staining (A), compared with membrane staining in areas that escaped Cre-mediated recombination (B). (C-E) The stomach is reduced in size and lined by a crowded, villiform epithelium (C,E; H&E stain) that shares features seen in Barx1 mutant stomach, including thick folds and mucosal invasion of the mesenchymal layer (E), which contrasts with relatively normal squamous differentiation (D) in many areas. (F) Radial asymmetry of E18.5 Shh^Cre/+;Catnb^+/lox(ex3) esophagus, with squamous (blue arrowheads) and cuboidal (green arrowheads) epithelia on opposite surfaces. (G) Magnification of the area boxed in F. PAS staining reveals many cells abnormally producing mucin in the cuboidal epithelium of the esophagus. (H-J) Although intestinal villi are absent, there is considerable and ectopic expression of the intestinal marker Cdx2 (H,I), which is normally excluded from the squamous (J) and glandular (data not shown) stomach. H is a magnification of the area boxed in C.