Conditional repression of NRAS^G12V expression induces apoptosis in the BM and circulating leukemia cells. (A) Apoptotic cell staining in the sternal BM with TUNEL method and Methyl Green as a counterstaining. Four days after Dox treatment, the number of apoptotic (brown) cells in the BM are increased in SCID mice transplanted with TRM-transgenic AML cells. Bars represent 50 μm. (B) Numerical comparison of apoptotic cells in BM. The average numbers of TUNEL-stained (TUNEL +) cells are shown with the standard deviation bars. The results indicate that conditional repression of NRAS^G12V expression significantly increases apoptotic death rates in the BM cells (P = .021). Apoptotic cell number is the average of stained cells in 3 fields. (C) Cleaved caspase-3 staining in peripheral WBCs. Apoptosis in peripheral bloods is observed 12 to 24 hours after Dox treatment. The number of apoptotic cells 12 to 24 hours is significantly increased in comparison with that of 0 to 6 hours (P = .045). The average number of apoptotic, cleaved caspase-3 positive cells was calculated by counting the stained cells in 41-45 fields at ×400 magnification. The narrow bars indicate the standard errors.