The intestinal epithelium is the most rapidly self-renewing tissue in adult mammals. The absorptive epithelium of
the small intestine is ordered into crypts and villi, which in the mouse turn over every three to five days. The
rapid rate of ceil production in the crypts is balanced by apoptosis at the tips of the villi.
Self-renewing stem cells cycle steadily to produce the cells capable of differentiating towards all types of
intestinal cells. . The estimated number of stem cells is between four and six per crypt:. Long-term DNA-
label retention has tentatively located stem cells directly above the Paneth cells’. Three differentiated cell
types (enterocytes, goblet cells and enteroendocrine cells) form from trans it-amplifying cells at the crypt-
villus junction and continue their migration in coherent bands stretching along the crypt-villus axis. Each villus
receives cells from multiple different crypts. The fourth principal differentiated cell type, the Paneth cell,
is at bottom of the crypt
The colon epithelium contains crypts, but has a flat surface rather than carrying villi. This epithelium
consists of two main differentiated cell types: the absorptive colonocytes and the goblet cells’. Until now, no
stem cells have been identified in the colon.
Using an intestinal target gene Lgr5 Barker et al have demonstrated that the crypt base columnar cell generated all
epithelial lineages over a 60-day period, suggesting that it represents the stem cell of the small intestine and colon.
Barker et al. ( 2007 ) Identification of stem cells in small intestine and colon by marker gene Lgr5 Nature vol 449,
- Martin Eastwood