GATA4 is excluded from the distal small intestinal epithelium during early development. Immunohistochemistry (IHC) for GATA4 (brown nuclear stain) is shown in tissue from the distal region of small intestine of E12.5 (n = 3) and E13.5 (n = 7) CD1 embryos. A 0.5 cm piece of small intestine dissected just superior to the cecum (red box) from each embryo was sectioned through its entirety and stained for GATA4. Tissue was also counterstained with hematoxylin. GATA4 was present throughout the region examined at E12.5 (panels A and B) although scattered cells within the most distal section of the tissue (panel B) had already lost GATA4 expression. By E13.5, GATA4 protein was absent from all cells in the most distal region of the small intestine (compare panels C and D). Insets show higher magnification images of boxed regions. S, stomach; SI, small intestine; Ce, cecum; LI, large intestine. Scale bars, 50 μm.