The beta-catenin--TCF-1 pathway ensures CD4(+)CD8(+) thymocyte survivalTranscriptional regulation of CD4 gene expression by T cell factor-1/beta-catenin pathway.Clonal acquisition of the Ly49A NK cell receptor is dependent on the trans-acting factor TCF-1Redundant functions of TCF-1 and LEF-1 during T and NK cell development, but unique role of TCF-1 for Ly49 NK cell receptor acquisition