Up-regulation of the Notch1 pathway at early phase of leukemogenesis and up-regulation of the Myc pathway at early and late phases of leukemogenesis. (A) GSEA histograms for the gene set “NOTCH signaling pathway.” The enrichment score (ES; y-axis) reflects the degree to which a gene set is overrepresented in normal control (N), polyclonal DP cells (P), and leukemic DP cells (L) at the extreme left or right of the entire ranked list. Each solid bar represents 1 gene within a gene set. Heat-map image illustrates gene expression levels of the leading edge subset. The normalized enrichment score (NES) and the nominal P value are indicated. (B) Expression of representative genes (Dtx, Hes1, Ptcra, and Snw1) in the Notch signaling pathway. Significance was evaluated by the Student t test: **P < .01. Data are mean ± SD values of triplicate experiments. (C) Expression of Myc and its targets (Apex1, Nme2, and Cdk4) in each cell. Significance was evaluated by the Student t test: *P < .05, **P < .01. Data are mean ± SD values of triplicate experiments. The NES and the nominal P value are indicated. (D) GSEA histograms for the gene set representing “MYC oncogenic signature.” See panel A description for details of the GSEA histogram.