Analysis of aging-associated phenotypes in Utx^Δ/ΔHSPCs. (A) Expression changes of Utx in young (2 months [M]) and aged (20 months) HSC subfractions. The results are shown relative to that in LT-HSCs. *P < .05. (B) Expression of CD41, an aging-related marker, in LSK-gated c-kit⁺ cells of aged (18 months) wild-type (WT) and young (2 months) Utx^+/+ and Utx^Δ/Δ mice. Representative results of fluorescence-activated cell sorting and a comparison of percentages of CD41⁺, LSK-gated c-kit⁺ cells in young Utx^+/+ and Utx^Δ/Δ mice are shown. **P < .01. (C) ROS levels in LSKs and LT-HSCs of Utx^+/+ and Utx^Δ/Δ mice. The representative histograms and fluorescence intensities are shown. **P < .01; ***P < .001. (D) Kinetics of DDR in Utx^+/+ and Utx^Δ/Δ LT-HSCs (0, 3, 18, and 24 hours) after 2 Gy of irradiation. Representative images of γH2AX (green) and 53BP1 (red) foci (top) and the number of γH2AX/53BP1-overlapping foci (bottom) in cells are shown, respectively. Residual γH2AX and 53BP1 foci in Utx^Δ/Δ cells at 18 hours after irradiation (arrow). **P < .01.