Exit from G₀/G₁ phases of cell cycle.

Exit from G₀/G₁ phases of cell cycle of total Sca-1⁺lin⁻ cells (▴), or engrafting phenotypes (dotted lines) and nonengrafting phenotypes (solid lines) of Sca-1⁺lin⁻ AM⁺ (▪) and AM⁻ (○) cells. Up to 4 × 10³ cells/mL were supplemented with 20% FBS, 2 × 10⁻⁵ mol/L 2-mercaptoethanol, 100 ng/mL mSCF and hIL6, 500 U/mL mIL1α, 100 U/mL mIL3, and 50 ng/mL hFlt3-L. Fresh cells and aliquots of cultured cells removed on days 1 and 2 were stained with propidium iodide and analyzed for cell cycle status as previously described.23 Data are expressed as the mean ± SEM; n = 2 to 3 for each time point. Slopes of linear regression lines generated from these data are indicated next to the appropriate lines to illustrate relative rates of exit from G₀/G₁ of the different populations of cells. *The presence of statistical significance in slope of regression line of engrafting phenotype when compared with the slope generated from its nonengrafting counterpart; P < .05.