Runx1-excised mice display myeloid expansion in spleen and liver. Spleen (A-B) and liver (C-D) sections from representative (A,C) Runx1^F/F and (B,D) Runx1^F/F—Tg(Mx1-Cre) mice 143 days after pIpC (H&E; original magnification, ×100). Insets' original magnification, × 600. (E-F) Spleen sections from representative mice 14 weeks after transplantation with (E) Runx1^F/F and (F) Runx1^F/F—Tg(Mx1-Cre) marrow (H&E; original magnification, × 100). Insets' original magnification, ×600. (A-F) Yellow arrows indicate representative lymphocytes. Red and green arrowheads indicate representative erythroid and myeloid elements, respectively. Sections demonstrate the presence of extramedullary hematopoiesis in the liver and splenic red pulp in Runx1-excised mice, absent in nonexcised control animals. (G) Gr1/Mac1 and CD45.2/Ter119 staining of splenocytes of indicated genotype from representative primary mice or mice that underwent transplantation. Numbers indicate percentage of cells gated in each respective quadrant.