Deletion of Notch1 accelerates T-ALL development. (A) Survival curves of Ik^L/LNotch1^f/fCD4-Cre⁺ (IN1C+), Ik^L/LNotch1^f/fCD4-Cre⁻ (IN1C⁻), and Ik^L/LNotch1^+/+CD4-Cre⁺ (IC⁺) mice. The P value corresponds to the statistical difference between the survival of IN1C⁺ and IN1C⁻ mice by log-rank test. (B) PCR analysis of the deletion of the floxed sequences in a panel of IN1C⁺ tumors. (C) Thymocyte CD4/CD8 profiles (top) and photos of the thoracic cavity (bottom) from 7-week-old WT, IN1C⁻, and IN1C⁺ mice. (D) Surface Notch1 and CD25 expression of IN1C⁺ and IN1C⁻ tumor cells and WT thymocytes. The immunoglobulin G isotype control is shown in the left panels. Similar results were observed in all Ik^L/L/IN1C⁻ and IN1C⁺ mice analyzed (n > 10). (E) Transcriptome profiling of Notch target genes in 3 IN1C⁺ and 3 IN1C⁻ tumors using Affymetrix 430 2.0 arrays. The data were normalized with those from leukemic T cells of Tel-Jak2 tg mice²⁴  and from WT DN3, DN4, and DP thymocytes using the Robust Microarray Analysis algorithm. Red and green colors indicate high and low expression, respectively. (F) Proliferation of IN1C⁺ and IN1C⁻ cell lines in the absence or presence of γ-secretase inhibitor over 6 days. Representative of 3 independent experiments. (G) Western blot of ΙCN1 expression in IN1C⁺ tumors using the Val1744 antibody. β-actin was used as a loading control. T99 is a IRC⁺ tumor that expresses ICN1 proteins of the normal 120 kDa size. The asterisk in the right panel points to likely degradation products. (H) PEST region sequences of IN1C⁺ tumors. The bold nucleotides correspond to insertions in the WT sequence. ICN1 proteins from samples T34, T6, and T49 are shown in supplemental Figure 1C; T51, T70 and T110 are shown in Figure 3G; T1 and T2 correspond to IN1C⁺ cell lines described in supplemental Figure 2. Numbering according to the Notch1 reference sequence NM_008714.