Regulation of intestinal stem cells by Wnt and Notch signalling.

The mammalian intestine is lined by an epithelial cell layer that is constantly renewed via a population of stem cells that reside in a specialised niche within intestinal crypts. The recent development of tools that permit genetic manipulation and lineage tracing of cells in vivo combined with culture methods in vitro has made the intestine particularly amenable for the study of signals that regulate stem cell function. Both Wnt and Notch signalling are critical regulators of stem cell fate. Gene knockout and transgenic expression analysis combined with meticulous analysis of lineage tracing and molecular characterisation has contributed to the definition of the mechanisms by which these pathways act during normal homeostasis and in disease states.