Derivation and lineage potential of BM-derived Csf1r^−/−progenitors. (A-B) W41 (CD45.1) mice were IV transplanted with 2 × 10⁷ E14.5 fetal liver cells of WT or Csf1r^−/− (CD45.2) genotype. Donor contribution was checked at various timepoints in recipients’ as follows: (B, left) peripheral blood (n = 3 to 6 per timepoint per genotype) or (B, right) BM (GMPs) (n = 3 per genotype) via flow cytometry. (C) Freshly isolated GMPs from C57Bl/6 (WT), W41 transplanted with WT fetal liver cells (WT [transpl.]), or W41 transplanted with Csf1r^−/− fetal liver cells (Csf1r^−/−) were cultured in methylcellulose containing either SCF, IL-3, IL-6, and EPO (left) or CSF-1 (right). After 5 to 7 days, colonies were enumerated and identified according to morphology (clonogenicity SCF IL-3 IL-6 EPO: WT = 45% ± 6.4% SD, WT [transpl.] = 47% ± 7.2% SD, Csf1r^−/− = 43% ± 4.4% SD; and clonogenicity CSF-1: WT = 46% ± 5.1% SD, WT [transpl.] = 47% ± 5% SD, Csf1r^−/− = 0, n = 3 per genotype per condition). P values are shown as follows: ***P < .001 compared with WT. Transpl, transplanted.