Morphologic comparison of E12.5 wild-type (WT) and AML1/EVI1^/+ heterozygous embryos. (A) External appearance of WT and AML1/EVI1^/+ littermates. AML1/EVI1^/+ embryo on the right is similar in size to WT littermate on the left but is clearly identifiable by the presence of fetal liver pallor and massive hemorrhage within the CNS and soft tissues in the back (objective lens [OL], 2 ×/0.05; original magnification [OL], × 20). (B-C) Sections of the cerebral ventricle from WT (B) and AML1/EVI1^/+ (C) embryos. AML1/EVI1^/+ embryo shows massive hemorrhage into the ventricle (OL, 10 ×/0.40; OM, × 100). (D-E) Sections of the dorsal root ganglia from WT (D) and AML1/EVI1^/+ (E) embryos. AML1/EVI1^/+ embryo shows hemorrhage in the ganglia (OL, 10 ×/0.40; OM, × 100). (F-G) Smears of the peripheral blood from WT (F) and AML1/EVI1^/+ (G) embryos. AML1/EVI1^/+ embryo shows the absence of definitive erythrocytes, while WT littermate shows numerous enucleated definitive erythrocytes (OL, 40 ×/0.65; OM, × 400). (H-I) Smears of the peripheral blood from WT embryo. Only WT littermate shows monocyte (H) and neutrophil (I) (OL, 100 ×/1.40; OM, × 1000). (J-K) Sections of the fetal liver from WT (J) and AML1/EVI1^/+ (K) embryos. AML1/EVI1^/+ embryo shows a near complete absence of hematopoietic precursors, while WT littermate shows numerous hematopoietic precursor cells (OL, 20 ×/0.70; OM, × 200).