Effect of hematopoietic growth factors (HGFs) on the growth of C/EBPα^-/- fetal liver (FL) cells in vitro. (A) FL cells were obtained from E16-E17 C/EBPα^-/- mice and seeded into soft agar colony assays at 5 × 10⁴ cells/mL in the presence or absence of 50 ng/mL human G-CSF (Amgen, Thousand Oaks, CA), 100 ng/mL M-CSF, 100 ng/mL murine SCF, 50 ng/mL murine GM-CSF, or 30 ng/mL murine IL-3 (Peprotech, Rocky Hill, NJ). (B) Bright field photomicrographs (× 16) of the 35-mm gridded (2 mm × 2 mm) plates were taken after 7 days. Dishes were incubated in a fully humidified atmosphere at 37°C, 5% CO₂, and then scored for colony formation after 7 to 10 days (culture colony-forming unit [CFU-C]). The results are presented as the mean number of colonies plus or minus the standard error, and are representative of at least 3 separate experiments.