PROJECT SUMMARY The colon is a major segment of the intestine and differs significantly from the small intestine in morphology, cell types, physiological function and disease susceptibility. Devastating and prevalent diseases, including colorectal cancers and ulcerative colitis, arise from colon but not small intestine. Colon absorbs water but cannot uptake most nutrients like the small intestine and consequently a significant loss of the small intestine will lead to digestive failure that the colon cannot compensate. Despite significant progress, aspects of the colon biology remain poorly understood. Molecular determinants that distinguish the colon from the small intestine and govern colon-specific cell lineage differentiation and homeostasis remain largely uncharacterized, hindering a deeper understanding of regionalized intestinal diseases. In preliminary studies, we identified SATB2, a chromatin factor with restricted expression in the colonic epithelium, as a crucial molecular regulator of colon identity and differentiation. SATB2 deletion from adult intestine led to a homeotic-like transformation of colonic epithelium into one that resembles small intestine ileum in cellular composition and gene expression, and the mutant colon can absorb nutrients, a function unique to the small intestine. These data suggest that SATB2 is a potential “master regulator” of colonic epithelium. The identification of SATB2 offers a unique opportunity to study colonic ontogeny and fate determination, and assess its therapeutic implications. In this project, Aim 1 will evaluate the hypothesis that colonic stem cells harbor primed ileal enhancers and thus harbor a chromatin-level permissiveness for ileal transcriptional activation and cell fate plasticity. Aim 2 studies will evaluate the hypothesis that SATB2 recruits two chromatin remodeling factors, MTA2 and SMARCD2, to separate pools of colonic and ileal enhancers to modify local chromatin, allowing differential access of intestinal transcription factors and effecting transcriptional regulation. In Aim 3, using mouse models of Short bowel syndrome (SBS), we will evaluate whether promoting colonic nutrient absorption can combat digestive failure and the associated pathophysiology in SBS. These studies together will elucidate the cellular and molecular mechanisms by which SATB2 preserves colonic identity and effects a colonic to ileal conversion, which may be exploited as a novel therapeutic approach to treat SBS.