Embryonic stem (ES) cells have the remarkable ability to differentiate into all of the cells of the body. During normal development, the differentiation choices of embryonic cells are influenced by extra-cellular factors. The aim of this grant is to understand how these extrinsic signals guide ES cells into differentiation pathways, in particular into endoderm. The endodermal lineage is the precursor tissue for the pancreas and the pancreatic islet cells that make insulin. We are focussing on the ability of Wnt proteins to control how ES cells differentiate, as these are powerful regulators of embryonic development. Our labs have the unique ability to use active Wnt proteins to study how they act directly on ES cells. Over the past year, substantial progress was made. The Nusse lab has shown that the self-renewal of embryonic stem cells, both human and mouse, is dependent on extrinsic Wnt signals. This finding has important consequences for the clinical application and transplantation of ES cells, as it suggests that antagonism of the Wnt pathway will force all pluripotent cells to differentiate, thereby eliminating their tumorigenic potential. Second, these results suggest that Wnts would act to promote the establishment new ES cells. Indeed, we have been able to readily establish various new ES lines from several different mouse strains. Over the next year, we will also attempt to derive new human ES cells based on this technology. The Wong group uses bio-informatic methods to analyze the differentiation of ES cells. They have developed new methods and computer programs to analyze gene expression data from new technologies. The Kim lab has developed a new ES clone, hS17-90 which differentiates into endoderm and characterized the gene expression profile of novel ES cells. These results may lead to a fine-tuned protocol to induce endodermal and pancreatic differentiation of ES cells. All three groups have made inroads into this research area and actively collaborate based on mutual interests and complementing technologies.