The small intestine can be divided in two parts: finger-like structures called villi cover the surface of the lumen and villi are surrounded by underlying pockets termed crypts. Both structures are covered with a columnar epithelium. The crypt base harbors LGR5+ stem cells and Paneth cells. Paneth cells are playing a very important role for stem cell function by secreting essential factors like Wnt, EGF and Notch ligands, and are also involved in the antimicrobial response. It has been shown that EGF is an essential survival factor for in vitro intestinal organoid cultures. However, its precise role for in vivo stem cell function has not yet been elucidated. I employed mice lacking the EGFR in different cell types of the intestine namely Lgr5+: (1) EGFRfl/fl LGR5CreERT2EGFP mice (2) EGFRfl/fl Villin Cre mice