Partial differentiation of Myc^V394D-AML cells compared with Myc-AML cells. MSCV-GFP/Cre^ERTMyc^fx/fx, Myc-GFP/Cre^ERTMyc^fx/fx, and Myc^V394D-GFP/Cre^ERTMyc^fx/fx AML cells were treated with 1 μM 4-OHT to induce the deletion of endogenous Myc. Beginning on day 2 following 4-OHT treatment, cells were collected for analysis at the indicated time points. Myc^fx/fx AML cells were studied in parallel as controls. (A) BrdU (final concentration 10 µM) was added to the culture to label the cells 2 hours before they were to be collected. The percentages of BrdU⁺ cells were analyzed by intracellular antibody staining and flow cytometric analysis. (B) Apoptosis was examined by annexin V staining. (C-D) Cells were collected on day 6 for morphologic (C) and phenotypic analysis (D). (E-F) One day after 4-OHT treatment, cells were collected and seeded for serial replating CFU assay (E). CFUs were counted on day 7 after plating. Cells were collected from the colonies of the third replating for morphologic study (F). (G) c-Kit⁺ HSPCs were collected from Cre^ERTMyc^fx/fx mice and cotransduced with RUNX1-ETO9a-GFP plus MSCV-mCherry, Myc-mCherry, or Myc^V394D-mCherry, respectively. The transduced HSPCs were purified by FACS and seeded into the methylcellulose with or without 4-OHT-induction. CFUs were counted 7 days after plating. Cells from the CFUs were collected for second and third replatings. **P < .01. 1st P/2nd P/3rd P, first plating/second plating/third plating.