Comparison of gene expression in cultured fetal and adult HSCs. Transcript levels were determined by Q-RT-PCR for each gene relative to Gapdh on the 48-hour progeny of highly purified suspensions of HSCs from E14.5 fetal liver (FL, □) and adult bone marrow (BM, ■) cultured under serum-free conditions with growth factors that optimize HSC maintenance (50 ng/mL SF for the fetal liver cells and 300 ng/mL SF plus 20 ng/mL IL-11 for the adult bone marrow cells). Lin⁻Sca1⁺CD43⁺Mac1⁺ cells were isolated from E14.5 fetal liver cells and lin⁻Rho⁻SP cells were isolated from adult bone marrow as described in “Materials and methods.” Results are the mean plus or minus SEM of data from 2 to 3 experiments, in each of which Q-RT-PCR measurements were performed in triplicate. Significant differences between fetal liver and adult bone marrow values (P < .05) were determined by a Student t test and are indicated by an asterisk.