The inner epithelial lining of the small intestine is a truly multitasking tissue. It must simultaneously achieve the efficient digestion (with the aid of enzymes released from the liver and pancreas) and the absorption of food contents released fromthe stomach while maintaining an effective barrier against potentially lethal microorganisms and carcinogens that are present in the intestinal lumen. Persistent aggression from the luminal contents induces a remarkably high rate of cell death, with up to 1011 epithelial cells (-200 g) being lost every day in humans.1 This imposes a requirement for daily self-renewal throughout life, which is driven by small populations of adult stem cells that reside within specialized niches. The ability of these stemcells to indefinitely self-renew while generating new functional epithelia makes them ideally suited for regenerative medicine applications. The same properties also make stem cells prime candidates for accumulating mutations that promote cancer growth— making them attractive therapeutic targets.
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