Elevated IRF8 causes aberrant myeloid differentiation potential of GATA2-deficient progenitor cells. (A) Experimental strategy for double mutant in vivo rescue system. Mice heterozygous for −77 enhancer deletion or Irf8^tm1.2Hm were bred to generate E14.5 embryos. Fetal liver progenitor populations with select genotypes were analyzed by flow cytometry. (B) Representative flow cytometry analysis of progenitor populations from GMPs (Lin⁻Sca-1⁻cKit⁺CD34⁺CD16/32^high). GPs and MPs are distinguished from multipotential GMPs by expression of Ly6C and from each other by M-CSFR (CD115). (C) Quantitation of the frequency of MPs and GPs within the Ly6C⁺ GMP populations from 7 litters (−77^+/+Irf8^+/+, n = 7; −77^−/−Irf8^+/+, n = 5; −77^+/+Irf8^−/−, n = 3: −77^−/−Irf8^+/−, n = 8; −77^−/−Irf8^−/−, n = 7). Relevant statistical comparisons for panel C are described in "Results." (D) Quantitation of colonies from sorted Ly6C⁻ GMPs plated in M3434 methylcellulose media (STEMCELL Technologies) at 1200 cells/plate. Colonies were scored as mixed-lineage CFU-GM, or single-lineage granulocyte CFU-G, or CFU-M colonies. Ly6C⁻ GMPs were obtained from 4 litters (−77^+/+Irf8^+/+, n = 6; −77^−/−Irf8^+/+, n = 8; −77^+/+Irf8^−/−, n = 6; −77^−/−Irf8^+/−, n = 5; −77^−/−Irf8^−/−, n = 6). Error bars for all plots represent mean ± standard error of the mean (SEM). *P < .05, **P < .01, ***P < .001, ****P < .0001; Welch’s unequal variance t tests.