Definitive erythropoiesis is defective in Mekk1^ΔKD and Mekk1^ΔKDJnk2^–/– embryos. Flow cytometry of FL hematopoietic cells from E13.5 wt, Mekk1^ΔKD, Jnk2^–/–, and Mekk1^ΔKDJnk2^–/– embryos and relative expression of globin genes in E13.5 FL of wt, Mekk1^ΔKD, Jnk2^–/–, and Mekk1^ΔKDJnk2^–/– embryos. (A) Expression of different cell-surface markers is depicted. Cell suspensions from E13.5 FLs were labeled with anti–c-kit, which marks hematopoietic stem cells; anti-CD44, which marks all hematopoietic cells; anti-Ter119, to identify differentiated erythroid cells; or anti-CD34 to mark hematopoietic progenitors. The dot plots represent the log fluorescence intensities of live cells. (B) Relative expression of globin chains was measured by real-time PCR. The ζ globin chain is found only in yolk sac–derived erythroblasts. The α globin chain is found in both yolk sac–derived and FL-derived erythroblasts. The β^major globin chain is found only in FL-derived erythroblasts and is continuously expressed until just prior to enucleation. GADPH mRNA levels were used for normalization in all cases. Percentage of cells in each quadrant is indicated. Data represent the average ± standard deviation (SD) from 3 to 5 animals per group.