Myeloerythroid development. (A) Whole WT FL mononuclear cells or BM cells were gated on viable, lineage⁻, c-kit⁺, and Sca-1⁻ cells, and representative staining patterns for CD16/32 and CD34 are presented. MEPs are defined as lineage⁻, c-kit⁺, Sca-1⁻, CD16/32⁻, and CD34⁻; GMPs are defined as lineage⁻, c-kit⁺, Sca-1⁻, CD16/32^hi, and CD34⁺; and CMPs are defined as lineage⁻, c-kit⁺, Sca-1⁻, CD16/32^lo, and CD34⁺. (B) FL or BM cells were isolated at the indicated time points, and the ratio of MEPs to GMPs is presented. *, P < 0.0001 by Student’s t test, comparing E14.5 FL and P42 BM time points. n = 6 animals for each time point over two experiments. (C) BM or FL cells were stained with the indicated antibodies (including erythroid and lymphoid lineage antibodies), and representative flow cytometry plots are presented. (D) FL or adult BM mononuclear cells were isolated at the indicated developmental time points, and the number of Gr-1⁺/Mac-1⁺ cells per 100,000 cells is presented. *, P < 0.001 by Student’s t test for E14.5 FL and P42 BM time points. n = 6 animals over two experiments. (E) FL or BM cells were stained with antibodies against Ter119 and CD71, and representative flow cytometry plots are presented. (F) The number of CD71⁺/Ter119⁻ cells in FL versus adult BM is presented. *, P < 0.0001 by Student’s t test. n = 6 animals over two experiments. (G) Mononuclear cells were cultured in methylcellulose for 14 d in the presence of growth factors (stem cell factor, IL-3, IL-6, and erythropoietin). Colonies were scored by morphology, and the proportion of each colony type in the cultures is presented. *, P < 0.05 for each colony type by Student’s t test. n = 4 adult BM and 6 E14.5 FL over two experiments. Error bars represent SEM. CFU-M, CFU monocyte; CFU-G, CFU granulocyte; CFU-GM, CFU granulocyte–monocyte.