Primitive erythrocytes persist in the circulation of 15.5-dpc ATF4^−/− embryos.

(A) Blood smears from 15.5-dpc embryos stained with Wright-Giemsa stain. The blood smear from a ATF4^−/− embryo (right) shows a greater than 2-fold increase in the percentage of nucleated erythrocytes compared with the sample from its wild-type littermate (left). Magnification 1000 ×. (B) HPLC analysis of globin chains. Blood from the 15.5-dpc ATF4^−/−embryo (right) had an increased level of embryonic globin chains (βh1, ε_y, and ζ) compared with blood from its wild-type littermate (left). The percentages of α globin chains that were embryonic (ζ) were 10.7% ± 1.6% in the ATF4^−/− embryo and 3.9% ± 0.8% and 5.1% ± 0.6%, respectively, in the wild-type and heterozygous embryos. The percentages of β globin chains that were embryonic (βh1 and ε_y) were 32.3% ± 3.7% in the ATF4^−/−embryo and 14.9% ± 2.9% and 12.0% ± 1.7%, respectively, in the wild-type and heterozygous embryos.