Final Report Summary - RAC1ISC (Rac1 function in Intestinal stem cells) Intestinal stem cells are crucial for the maintenance of the intestinal epithelium and are suggested to play an important role in colon cancer formation. To understand the role of the small Rho GTPase Rac1 and the potential Rac1 effector N-WASP in intestinal stem cells, we generated mice with a deletion of these genes in intestinal stem cells. These mice were furthermore crossed with APCmin mice, which spontaneously develop intestinal tumors. To complement in vivo results with functional in vitro studies, a state-of-the-art organoid in vitro culture system was established, which allowed long term culture of intestinal stem cells. Test to manipulate these cells through retroviral infection, however, were only poorly effective. The project was stopped after 6 months since the post doc received a job offer from industry that she could not refuse.