Loss of SKP2 differentially affects cell-cycle kinetics in distinct hematopoietic subsets. In vivo BrdU incorporation and DNA content were analyzed in immunophenotypically defined hematopoietic subsets from Skp2^+/+, Skp2^+/−, and Skp2^−/− mice: (A) LSK. Left, representative dot blot of BrdU analysis gated on LSK cells. Numbers indicate the percentage of LSK cells in each quadrant; left top quadrant indicates early S-phase; right top quadrant indicates late S-phase. Bar graph on the right summarizes average percentage of LSK cells positive for BrdU and shows distribution between early S-phase (top light columns in the bar) and late S-phase (bottom dark columns in the bar); (B) LK. On the left, histogram shows BrdU incorporation in LK cells in a representative experiment; overlaid are intensity of BrdU fluorescence in LK Skp2^−/− cells (red) and of BrdU fluorescence LK Skp2^+/+ cells (blue). Bar graph on the right summarizes the average percentage of LK cells positive for BrdU as in panel A. (C) Lin⁻ cells. On the left, histogram shows BrdU incorporation in Lin⁻ cells in a representative experiment. Lin⁻ cells were purified and subjected to a BrdU pulse for 3 hours. Bar graph on the right summarizes average percentage of Lin⁻ cells positive for BrdU. (A-C) n = 6 in 4 independent experiments. (D) Lin⁻ purified cells were starved overnight with 2% FBS media supplemented with SCF and then stimulated with SCF and IL-3 for 0, 12, and 24 hours. Line graph summarizes average percentage of cells positive for BrdU. On the right, dot blot shows BrdU incorporation in a representative experiment. n = 5 in 2 independent experiments. All values are expressed as mean ± SEM *P < .05 vs Skp2^+/+.