The intestinal epithelium is characterized by a remarkable self-renewal capacity and a continuous high turnover of intestinal epithelial cells (IEC), which emerge from intestinal stem cells (ISC). The presence of ISC and appropriate stimuli for proliferation and differentiation along the crypt-villus axes are absolutely essential for the functionality of the system. Not surprisingly, factors interfering with this highly dynamic network limit epithelial regeneration and can lead to the disruption of the epithelial barrier, which is a hallmark of several disorders of the gastrointestinal tract including inflammatory bowel disease (IBD). Glycoprotein (GP)96 is an endoplasmatic reticulum (ER) resident protein that acts as a master chaperone for cell surface receptors including toll-like receptors (TLRs), integrins and the Wnt co-receptors LRP5/6. Recent, unpublished data from our group show that IEC-specific deletion of GP96 in adult mice results in loss of ISC and proliferating IECs, followed by a complete eradication of the epithelial layer and the mice die within few days. Based on these findings, the aim of the project is to further investigate the role of GP96 in IECs and in maintaining homeostasis of the intestinal epithelial structure. Elucidating molecular mechanisms that define the fate of the ISC niche will not only crucially promote our understanding of intestinal barrier physiology, but also give insight on the mechanisms involved in the development of diseases that involve intestinal barrier defects, such as IBD.