Adult mouse expression pattern of Wnt-receiving epithelial cells. (A,C,D) Cryopreserved adult TOPGAL mouse proximal small intestinal (PSI) or colonic and (B) BatGal mouse PSI tissue sections were stained with antibodies against β-galactosidase (β-gal, red) and counterstained with Hoechst dye (blue). (A,B) The majority of crypts in the PSI contained only one Wnt-activated cell or was devoid of positive cells (arrow). There were occasional mesenchymal cells positive for β-gal (arrowhead) in BatGal intestines (B). (C) Occasionally, β-gal-expressing cells were detected throughout the crypt epithelium and on adjacent villi. (D) Colonic crypts contained only rare single β-gal positive cells near the crypt base. (E) Wnt-receiving cells detected by enzymatic activity, X-gal staining (blue, arrow). (F) Adult wild-type mouse PSI was stained with antibodies against β-catenin (brown; arrow) to detect nuclear expression and counterstained with Hematoxylin. (G-I) Analyses of reporter RNA expression pattern and localization was determined by in situ hybridization (G,H; purple, arrow) and are consistent with the expression pattern in (A). (I) qRT-PCR for lacZ gene expression in isolated crypt or villus epithelial cells from TOPGAL PSI demonstrated expression in the crypts. (J) The crypt localization of β-gal-positive cells was highest in the lower third and decreased in numbers in the middle and upper third. (K) Crypts with Wnt-receiving cells in TOPGAL intestinal sections were higher in the PSI (15.2%) and decreased down the length of the intestine to 0.8% in the colon. (L) The number of β-gal-positive villi also reflected a decreasing gradient with the highest numbers in the PSI (12.3%), less in the the middle small intestine (MSI; 4.0%) and the least in the distal small intestine (DSI; 0.2%). Solid white or black line demarks the epithelial-mesenchymal boundary. Dashed line outlines the apical epithelial border. Bar = 25 μm.