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Hematology - Immunology

Notch3 Is Dispensable for Thymocyte ß-Selection and Notch1-Induced T Cell Leukemogenesis
Published: Tuesday, September 13, 2011
Author: Sara Suliman et al.

by Sara Suliman, Joanne Tan, Keli Xu, Philaretos C. Kousis, Paul E. Kowalski, Greg Chang, Sean E. Egan, Cynthia Guidos

Notch1 (N1) signaling induced by intrathymic Delta-like (DL) ligands is required for T cell lineage commitment as well as self-renewal during “ß-selection” of TCRß+ CD4-CD8- double negative 3 (DN3) T cell progenitors. However, over-expression of the N1 intracellular domain (ICN1) renders N1 activation ligand-independent and drives leukemic transformation during ß-selection. DN3 progenitors also express Notch3 (N3) mRNA, and over-expression of ligand-independent mutant N3 (ICN3) influences ß-selection and drives T cell leukemogenesis. However, the importance of ligand-activated N3 in promoting ß-selection and ICN1-induced T cell leukemogenesis has not been examined. To address these questions we generated mice lacking functional N3. We confirmed that DN3 progenitors express N3 protein using a N3-specific antibody. Surprisingly however, N3-deficient DN3 thymocytes were not defective in generating DP thymocytes under steady state conditions or in more stringent competition assays. To determine if N3 co-operates with N1 to regulate ß-selection, we generated N1;N3 compound mutants. However, N3 deficiency did not exacerbate the competitive defect of N1+/- DN3 progenitors, demonstrating that N3 does not compensate for limiting N1 during T cell development. Finally, N3 deficiency did not attenuate T cell leukemogenesis induced by conditional expression of ICN1 in DN3 thymocytes. Importantly, we showed that in contrast to N1, N3 has a low binding affinity for DL4, the most abundant intrathymic DL ligand. Thus, despite the profound effects of ectopic ligand-independent N3 activation on T cell development and leukemogenesis, physiologically activated N3 is dispensable for both processes, likely because N3 interacts poorly with intrathymic DL4.