Fig. 3. Differentiation of goblet cells but not colonocytes and enteroendocrine cells was abnormal in Klf4^–/– mice. (A,B) Hematoxylin and Eosin staining of the colon from postnatal day 1 mice. (A) The colonic epithelium of wild-type mice showed a normal contour and numerous goblet cells (arrows) along the crypts and surface epithelium. (B) By contrast, goblet cells were nearly absent from Klf4^–/– epithelium, and mutant mice appeared to have subtle changes in epithelial contour. Colonocytes appeared grossly normal. (C,D) Immunohistochemistry for chromogranin A, a marker of enteroendocrine cells, in colon from postnatal day 1 mice. Enteroendocrine cells (arrows) were identified in both wild-type (C) and Klf4^–/– mice (D). In both cases, enteroendocrine cells were seen at typically low numbers, with only one to two enteroendocrine cells per transverse section.