Colonic crypts do not contain Paneth cells, and the stem cells in the colon have been localized to the base of the crypt (Korinek et al.1997, Science, 275, 1784). The approximate location of stem cells in the small intestine is at position 4 from the crypt base above the differentiated Paneth cells. Lineage tracing experiments in both the small intestine and the colon have led to the conclusion that stem cells reside near the crypt base. (B) Schematic representation of a small intestinal crypt. (A) Drawing showing the relationship between small intestinal villi and crypts. The stem cells may be maintained at the base of crypts, embedded in the intestinal wall, for protection from toxins passing through the gut lumen.įigure 6.4. Migration of these transit-amplifying cells out of the proliferative zone is required for the onset of differentiation ( Figure 6.4B). Within a crypt, approximately 4–5 stem cells generate transit-amplifying cells, which are capable of up to six transit divisions. However, lineage tracing experiments have located the presumptive stem cells of both the small intestine and the colon near the base of each crypt. No cell-specific marker has been characterized that allows conclusive identification and characterization of intestinal stem cells. Intestinal cells leave the crypt at a rate of 200–300 cells/day and migrate onto ciliated villi that protrude into the gut lumen ( Figure 6.4A). The inner lining of the colon and small intestine is a simple columnar epithelium constantly renewed by the proliferation of stem cells residing within pockets, or crypts, along the intestinal wall.
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