Kinetics of colony formation by primitive hematopoietic stem cells from c-fos–deficient mice. Lin⁻Sca-1⁺ cells (3 × 10²) from FL of c-fos–deficient mice or control littermates were cultured with SCF, IL-3, and IL-6 (□), or IL-3 alone (▪). The number of colonies was scored and plotted. Results represent mean and SD of four dishes. The data presented are representative of three independent experiments.