Proliferation and apoptosis of Ku70^−/−HSCs/progenitors. (A) BM cells were isolated from 3-month-old Ku70^−/− and WT mice and subjected to FACS analysis after treatment with Hoechst 33342 and Pyronin Y and staining with surface markers. Three separate experiments were performed with 3 to 5 mice per genotype compared. LSK and SLAM-LSK cells were analyzed by Ho33342 contents and pyronin Y intensity, and the proportion of cells in G₂/S/M or G₀/G₁ phase was quantitated. Error bars indicate the SD, and significance was determined by a 2-tailed Student t test. *P < .05. (B) BrdU incorporation. WT (n = 5) and Ku70^−/− (n = 3) mice were injected and fed with BrdU for 30 hours. BM cells were isolated and BrdU+ proportion within LSK fraction was analyzed. (C) BM cells from Ku70^−/− and WT mice were isolated and subjected to FACS analysis after staining with surface markers along with annexin V and DAPI. The proportion of annexin V–positive (DAPI-negative) cells within the LSK and SLAM-LSK fraction is quantitated. Error bars indicate SD, and significance was determined by a 2-tailed Student t test.