Fig. 3. Ki67, Cdc6, Cdt1, Mcm2 and Geminin protein expression in human colonic mucosa (original magnification x144). The schematic drawing of a colonic crypt (cross section; top left) shows the basal proliferative compartment (BC; white star) containing stem-transit progenitor cells and the luminal compartment (LC; black star) containing differentiating goblet and enteroendocrine cells. A large proportion of cells in the BC express Ki67. The majority of basal cells and a subset in the LC express Mcm2 and Cdt1. Geminin expression is restricted to a subset of cells in the BC. Cdc6 expression is restricted to basal proliferating cells. Note the absence of origin licensing factors at the base of the crypts (putative stem cell compartment).