Characterization of purified LSKs, CLPs and CMPs. (A) Colony-forming activities of LSKs, CLPs and CMPs. Sorted cells were seeded at a density of 1000 cells/ml in methylcellulose medium containing IL-7, SCF and VEGF for lymphoid assays (pre-B cell mix), and IL-3, IL-6, SCF and Epo for myelo-erythroid assays (GM, M, Mix, BFU-E). Colonies were scored at days 8–10. The results are represented as the mean value of four independent experiments. (B) Expression of c-fms mRNA in purified LSKs, CLPs, CMPs, pro-B cells and macrophages (Mø). Gene expression was measured by RT–PCR. Arbitrary units were calculated relative to the expression level in CMPs. The bars represent the mean value of two independent experiments.