To test whether this pathway is functional in vivo we turned to the small intestine for following reasons: enterocytes express Dab1 throughout the intestinal mucosa [22] and its expression is strongly induced in colorectal cancer [24]; furthermore, Paneth cells, which constitute the niche for intestinal stem cells in intestinal crypts, secrete Wnt3, TGFα, the Notch-ligand D114, and EGF [34]. Here, EGF is linked to colorectal cancer.