Weak, nonleukemogenic Notch alleles and strong, leukemogenic Notch alleles progressively deplete HSC activity and numbers over time. (A) Lethally irradiated mice were reconstituted with 5-FU–treated donor C57BL/6 BM cells transduced with MigR1 control or activated Notch1 (ΔEGFΔLNRΔP). BM cells at 6 weeks after transplantation were analyzed for donor-derived hematopoietic progenitor cells (GFP⁺Lineage⁻Sca-1⁺c-Kit⁺). Representative flow cytometry plots are shown. (B-C) Lethally irradiated CD45.1⁺ congenic mice were reconstituted with 5-FU–treated donor Rag1^−/− CD45.2⁺ BM cells transduced with MigR1 control or activated Notch1 alleles (ΔEGFΔLNR, ΔEGFΔLNRΔP, and ICN). At 6 weeks (B) and 13 weeks (C) after transplantation, cells were gated on the HSC compartment (Lineage⁻Sca-1⁺c-Kit⁺Flt3⁻) and analyzed for donor reconstitution (GFP⁺). Experiments were performed twice.