Inactivation of Notch I in immature thymocytes does not perturb CD4 or CD8T cell development

Notch proteins influence cell-fate decisions in many developing systems. Several gain-of-function studies have suggested a critical role for Notch1 signaling in CD4-CD8 lineage commitment, maturation and survival in the thymus, However, we show here that tissue-specific inactivation of the gene encoding Notch1 in immature (CD25(+)CD44(-))T cell precursors does not affect subsequent thymocyte development, Neither steady-state numbers nor the rate of production of CD4(+) and CD8(+) mature thymocytes is perturbed in the absence of Notch1, In addition, Notch1-deficient thymocytes are normally sensitive to spontaneous or glucocorticoid-induced apoptosis, In contrast to earlier reports, these data formally exclude an essential role for Notch1 in CD4-CD8 lineage commitment, maturation or survival.