In addition to working together to drive expression of target genes, -catenin and TCF often work independently of each other. They both regulate several stages of T cell development, but their mode of action remains poorly understood. To study the specific role of -catenin-TCF interactions in T cells, we generated transgenic mice that express ICAT, a naturally occurring inhibitor of -catenin-TCF interactions, in the T cell lineage. We found that -catenin-TCF interactions are important for thymocyte survival, but not for proliferation or differentiation. Interestingly, thymocyte aging slows...