mTOR activity in WT and KO progenitors. BM cells were isolated from 2-month-old WT or KO mice and stained with Abs specific to cell-surface markers to identify c-Kit⁺lin⁻Sca-1⁺ (KLS) progenitors, followed by intracellular staining with Abs against (A) p-mTOR and (B) p-S6. (Left side) Histograms of progenitors (KLS) that are representative of 3 independent experiments each involving 3 to 5 mice in each group. Gray and black lines are negative controls (secondary Ab only for panels A and B), black line for cells from WT mice and gray line for cells from KO mice. Blue line represents profile of stained BM cells from WT mice and red line represents profile of stained BM cells from KO mice. The median fluorescence intensity (MFI) ± SD of representative of one experiment is shown at the right side. **P < .01; *P < .05 (n = 4 WT and n = 4 KO).