Modification of the inner epithelial cells upon activation of Wnt. At the ultrastructural level, alteration of the Wnt pathway induces polarity changes of cells composing the thickening of the atrial epithelium of the inner vesicle of the primary bud. The normal pattern of cells oriented toward the outer side of the budlet (A) is mostly lost in drug-treated colonies (C). Particularly, in drug incubated animals (D), epithelial cells lose their nuclei orientation compared to the control animals (B). The collagen content (asterisks) in treated samples is thinner compared to the non-treated tissues. Shallow intercellular junctions (arrows) are visible in both preparations showing no structural differences. BAR: 10 micron (A and C); 1 micron (B and D).