Identification and characterization of intestinal and colonic stem cells

Over the last decade, the notion that tissue regeneration or healing is maintained by organ specific stem cells, the so-called "tissue stem cells", has created great excitement in the medical community. Tissue stem cells are characterized by the ability to give rise to multiple cell types and have self-renewing ability. In the intestinal tract, the stem cell pool is thought to comprise of both rapidly dividing "active" stem cells, as well as more "quiescent", slow-dividing master stem cells that are available in times of stress or injury. Despite the importance of tissue stem cells in homeostasis and disease, identification of these cells has proven challenging as these cells are not readily distinguishable from other cells. Recent work has demonstrated that the protein Lgr-5 marks a group of actively dividing stem cells known as the crypt base columnar cells. Nevertheless, it remains unknown whether there is more than one stem cell pool or long-lived quiescent stem cells within the intestinal crypt. Our group has focused on the protein cytokeratin-19 (K19) that is an intermediate filament critical to the cell cytoskeleton. We recently showed that K19 labels cells near the crypt base, and we hypothesize that K19 labels intestinal and colonic stem cells. Thus, we will use K19-BAC-CRE and K19-BAC-CreERT2 transgenic mice to genetically label K19+ intestinal and colonic stem cells following tamoxifen administration. We will also assess the contribution of K19+ cells to cancer upon targeted introduction of genetic mutations in K19 expressing cells. Finally, we will compare K19+ and Lgr-5+ cells with respect to stem cell properties and RNA expression profiles to better characterize these two populations. We aim to show that K19 labels a unique population of intestinal and colonic stem cells and examine their role in injury and cancer. These studies will help shed light on the cellular origin of colon cancer, and identify novel therapeutic targets for treatment.