Loss of HNF4α disrupts the normal differentiation of the mucous neck cell/zymogenic cell lineage. A: H&E + periodic acid Schiff (to detect mucins) of mouse gastric epithelium in control and ΔHNF4α mice. Brackets highlight higher magnification views, below, of bases of gastric units. Isolated bases (labeled “ZCs”) and random PCs from the images are shown side by side at the same magnification. Note that ZCs are smaller in ΔHNF4α mice, whereas PCs do not show morphological changes. Scale bars = 50 μm. B: immunofluorescent stain of the ER marker Calregulin (red) and the mucous neck cell marker GSII (green) in ΔHNF4α mice. Note that mucous neck cells show aberrant localization to the base of the unit, within the ZC zone (white arrowhead), also visible by PAS staining for mucus in C (e.g., yellow arrowhead). Scale bars = 20 μm.