Absence of Runx1 favors monopoiesis over granulopoiesis. (A) Marrow mononuclear cells from Runx1(f/f) or Runx1(f/f);Mx1-Cre mice exposed to pIpC were assessed for myeloid progenitor numbers in IL-3, IL-6, and SCF per 1E4 mononuclear cells plated (mean and SE from 3 determinations). (B) Pooled CFUs were subjected to FACS analysis for Mac-1 and Gr-1. The proportions of Mac-1⁺Gr-1⁻ monocytes (M) and Mac-1⁺Gr-1⁺ granulocytes (G) are indicated. (C) CFUs were cytospun and subjected to Wright-Giemsa staining. (D) Marrow mononuclear cells from Runx1(f/f) or Runx1(f/f);Mx1-Cre mice exposed to pIpC were subjected to similar FACS analysis immediately after isolation. The proportion of Mac-1⁺Gr-1⁻ monocytes relative to the sum of monocytes and granulocytes is shown (mean and SE from 6 determinations). (E) Control or Runx1-deleted marrow cells were lineage-depleted and placed in liquid culture with IL-3, IL-6, and SCF and subjected to FACS analysis 4 days later. Representative data (left panels) and a summary of 3 determinations (right graph) are shown. (F) Viable cell numbers were enumerated immediately after lineage depletion of control or Runx1-deleted cells and 2 or 4 days later. A representative growth curve is shown.