Mekk1^ΔKD and Mekk1^ΔKDJnk2^–/– embryos are anemic and exhibit a striking increase in the number of nucleated erythrocytes. (A) E14.5 wt, Mekk1^ΔKD, Jnk2^–/–, and Mekk1^ΔKDJnk2^–/– mouse embryos (Theiler stages 1, 2). Note the absence of color in major blood vessels, the general paleness, and the smaller liver of the Mekk1^ΔKD and Mekk1^ΔKDJnk2^–/– embryos. Also note the erythroplaki of the Mekk1^ΔKDJnk2^–/– embryo. (B) Sections through major blood vessels of wt and Mekk1^ΔKD (E15.5), and Jnk2^–/– and Mekk1^ΔKDJnk2^–/– (E14.5) embryos stained with H&E. Note the almost complete absence of enucleated erythrocytes in the Mekk1^ΔKD and Mekk1^ΔKDJnk2^–/– embryos. Bar = 75 μm. (C) Subcutaneous sections of wt, Mekk1^ΔKD (E15.5), Jnk2^–/–, and Mekk1^ΔKDJnk2^–/– (E14.5) embryos stained with H&E. Note marked decrease in the number of circulating erythrocytes in the Mekk1^ΔKD and Mekk1^ΔKDJnk2^–/– samples. Bar = 100μm. (D) Subcutaneous panendothelium stained sections of E13.5 wt, Mekk1^ΔKD, Jnk2^–/–, and Mekk1^ΔKDJnk2^–/– embryos. Bar = 100 μm.