GATA-4 and GATA-6 mRNA expression in normal gastrointestinal mucosa. Both bright and dark field in situ hybridization views are shown. In the stomach (A, A', B, and B'), GATA-4 mRNA expression is strongest in the middle and superficial layers (A-A'), while GATA-6 mRNA expression is most abundant in the basal two thirds of the mucosa (B-B'). In the duodenum, the enterocytes lining the villi are strongly positive for GATA-4 (C-C'), whereas the GATA-6 signal is more diffuse (D and D'). GATA-4 is no longer detected in the ileum (E and E') and colon (G and G'); the bright lining on the surface of the mucosa is due to tissue autofluorescence (E-E' and G-G'). In contrast, GATA-6 expression is prominent both in the small (D, D', F, and F') and large intestine (H and H') presenting positivity in the surface and crypt enterocytes, and the cells of the lamina propria (D-D', F-F', and H-H'). Scale bar = 50 μm. Abbreviations: STO = stomach, DUO = duodenum, ILE = ileum, COL = colon.