Notch1 target gene expression is repressed in GSI-treated leukemic Tal1/Ink4a/Arf^+/− mice. At killing, thymomas were harvested from vehicle- and MRK-003–treated mice and c-Myc (A), Pre-Tα (B), Deltex1 (C), and Hes1 (D) expression was quantified using real-time PCR. The copy number for each target gene was normalized to the copy number for β-actin using the ΔΔCT method. The following result is an average of 3 independent experiments. The mouse T-ALL cell line 720 was treated in vitro with 1 μM MRK-003 or DMSO for 72 hours and used as a positive control in these experiments.