Inhibitory effect of c-fos on the stroma-dependent hematopoiesis by primitive hematopoietic stem cells. Lin⁻Sca-1⁺ BM cells (3 × 10² cells/well in 6-well tissue culture plate) were cultured on a PA-6 stromal-cell layer in the presence (closed square; 200 U/mL) or absence (□) of IFN-/β. On day 12 of culture, the cells from Mx–c-fos culture with IFN-/β were obtained and washed with medium, and continued to culture on the PA-6 stromal layer with (▪) or without (○) IFN-/β. Nonadherent cells obtained from at least four dishes by gentle pipetting at every medium change were rinsed once with medium, pooled, and counted. The data presented are representative of three independent experiments.