Time course of changes in HSC activity under different concentrations of SF. (A) Single cells or their clonal progeny were injected after 8, 16, or 96 hours of culture in 20 ng/mL IL-11 plus either 300 ng/mL (blue) or 10 ng/mL (red) SF. Each data point represents the percentage of positive transplants (number of positive mice as a proportion of the total analyzed) for each condition and time point assessed. The straight line across the graph represents the starting HSC content as determined by single-cell transplants of freshly isolated CD45^midlin⁻Rho⁻SP or CD45^midRho⁻EPCR⁺⁺ cells. *Value significantly different (P < .05) from the input HSC frequency. (B) Q-RT-PCR analyses of transcript levels in extracts of cells harvested from 16-hour cultures initiated with CD45^midRho⁻EPCR⁺⁺ cells and maintained in 20 ng/mL IL-11 plus 300 ng/mL (blue bars), 10 ng/mL (red bars), or 1 ng/mL SF (brown bars). All values normalized to Gapdh. ND indicates not detected. Values shown are the mean plus or minus SEM values obtained in 2 or 3 independent experiments, with each measurement derived from triplicate assays. Data without error bars are from a single experiment.