Small intestinal development in the young chick: crypt formation and enterocyte proliferation and migration

1. Post-natch mucosal development was examined in the chick small intestina l epithelium using immunostaining with proliferating cell nuclear antigen ( PCNA) and 5-bromo-2-deoxyuridine (BrdU). 2. On the day of hatching jejunal crypts were small and a single crypt per villus was observed. However, during the 108 h post-hatch crypts developed rapidly, branching and increasing in size, cell numbers and cell size. 3. Almost all epithelial cells in the small intestine of the hatching chick were proliferating, as indicated by PCNA and BrdU, while more than 80% of proliferating cells were localised in the crypts after 108 h post hatch. 4. Estimate of villus cell transit time using BrdU was only possible from 4 8 h post-hatch when villus transit time was 72 h in the jejunum, whereas at 336 h transit time was 96 h. 5. In the 108 h post hatch a rapid transition occurs from total jejunal epi thelial cell proliferation and immature crypts to a defined proliferative z one in the crypts, with constant division and migration.