Fig. 4. Comparative histology of P15 stomach (A-L) and P30 proximal colon (M,N) of wild-type (A,C,E,G,I,K,M) and Hoxa5^–/– mutants (B,D,F,H,J,L,N). Sections from zymogenic zone of the stomach were stained for representation of cell lineages: Hematoxylin and Eosin (A,B), Periodic acid/Schiff (C,D; mucus cells), and silver staining (G,H; enteroendocrine cells). IF immunostaining detected zymogenic cells (E,F). Proliferating cells were revealed by immunostaining with a pH3 antibody (I,J), and apoptotic cells by the TUNEL method (K,L). Hoxa5^–/– stomach was characterized by a thinner epithelial layer and an hypertrophied submucosal layer (A,B), more mucus producing cells (C,D; arrowheads), an altered distribution of zymogenic cells along the gastric unit (E,F; arrows), and a decreased number of enteroendocrine cells (G,H; arrows). Proliferation in the isthmus (I,J; arrows) and apoptosis (K,L; arrows) were both reduced. In the proximal colon, abnormal distribution of goblet cells was noted in the Hoxa5^–/– epithelium, as revealed by Alcian Blue staining (M,N; arrowheads). Scale bars: 100 µm.