All stromal layers support the proliferation and differentiation of MK-committed progenitors. (A) Gating strategy for the isolation of 2 populations of MK-committed progenitors. Bone marrow Lin-depleted cells were labeled for sorting of a population enriched in MK erythroid bipotent progenitor (MEP) identified as Lin⁻CD16/32⁻Sca-1⁻ckit⁺CD150⁺CD9^dim and a population of unipotent MK precursor (MKP) cells identified as Lin⁻CD16/32⁻Sca-1⁻ckit⁺CD150⁺CD9^bright. Dot plots are representative figures with the mean ± SEM from 5 independent experiments. (B) MEP or MK precursors were plated in low-cytokine medium onto stromal layers and cultured for 3 days. (C) The bar graph represents the total number of cells produced. Values represent mean ± SD from 10 independent experiments. *P < .01 vs the nonstroma group. Other comparisons were not statistically significant. (D) The bar graph represents the total number of mature MKs. Values represent mean ± SD produced from 10 independent experiments. *P < .05 vs the nonstroma group; #P < .05 vs stroma V⁺P⁻. Other comparisons were not statistically significant. CK, cytokine; NS, no stroma.