CELL-PROLIFERATION IN CHICKEN INTESTINAL EPITHELIUM OCCURS BOTH IN THE CRYPT AND ALONG THE VILLUS

The location of cell proliferation and differentiation in chicken smal l intestinal epithelium was examined using immunostaining, measurement of DNA synthesis and brush-border enzyme activities. Chicken enterocy tes were removed sequentially from the villus using a modification of the Weiser (1973) method. Alkaline phosphatase activity was relatively constant along the villus tip-crypt axis but decreased in the crypt f ractions, whereas sucrase and maltase activities showed higher activit y in the upper half of the villus and lower activity in the lower half of the villus and in the crypt. Immunostaining of proliferating cell nuclear antigen indicated the presence of proliferating cells both in the crypt and along the villus, including some activity in the upper p ortion, the crypt region exhibited a significantly higher number of pr oliferating cells. Labelled thymidine incorporation into cell fraction s after 2 h incubation exhibited a similar pattern of proliferation, w ith the most active region observed in the crypt and proliferation act ivity decreasing along the villus. However, some activity was found in the upper half of the villus. After 17 h incubation, cells from the m iddle region of the villi showed greater proliferation ability than th e 2 h incubation. These results indicate that, unlike mammals, chicken enterocyte proliferation is not localized only in the crypt region, a nd that the site of enterocyte differentiation is not precisely locali zed.