Renewal of the epithelium of the descending colon of the mouse.

The renewal of various types of epithelial cells was examined in the descending colon of adult mice given 3H-thymidine. Semi-thin Epon sections were stained with PA-Schiff-iron-hematoxylin and radioautographed. The existence of three cell lines was established: vacuolated columnar, mucous and enterochromaffin. In the vacuolated-columnar cell line, only vacuolated cells divide. A vacuolated cell at the cryptal base and its progeny would go through three mitotic cycles in the lower two-thirds of the crypt before becoming columnar cells. In the mucous cell line, cells originate from vacuolated cells in the lower one-third of the crypt and undergo one or two mitotic cycles before ceasing to divide. Enterochromaffin cells do not divide, but renew by differentiation of vacuolated cells. The proliferative rate of epithelial cells undergoes diurnal variation, which affects mucous cells more seriously than vacuolated cells. All epithelial cells migrate upward along the cryptal wall, and eventually are lost from the surface