Mouse embryonic globin gene expression in yolk sacs from EKLF^−/−KLF2^−/− compared with wild-type and single knockouts. (A) Ey-globin mRNA, (B) βh1-globin mRNA, (C) ζ-globin mRNA. Glycophorin A (GPA) mRNA was used as an internal standard for quantitative RT-PCR. The globin-to-GPA mRNA ratio for wild-type (□) was taken as 100%, and for the other genotypes is expressed compared with 100%. To maintain similar genetic backgrounds between test and control samples, all mutants are compared with wild-type littermates. The other genotypes are EKLF^+/−KLF2^+/− (▨, n = 8), KLF2^−/− (▩, n = 7), EKLF^−/− (, n = 4), and EKLF^−/−KLF2^−/− (■, n = 6). n represents the number of embryonic yolk sacs of each genotype used to determine the mean globin-to-GPA mRNA ratio. Error bars represent the standard deviation from the mean. The asterisks in panels A and B indicate a significant reduction in Ey- and βh1-globin mRNA (P < .025) in double- compared with single-knockout embryos. The asterisk in panel C indicates a significant reduction in ζ-globin mRNA in EKLF^−/− compared with wild-type. (D) Mouse glycophorin A (GPA) gene expression in E10.5 EKLF^−/−KLF2^−/− yolk sacs. Cyclophilin A mRNA was used as an internal standard for quantitative RT-PCR. Wild-type (□, n = 5) and EKLF^−/−KLF2^−/− (■, n = 5) embryonic yolk sac RNAs were tested to determine the mean GPA-to-cyclophilin A mRNA ratio. Error bar is standard deviation, and wild-type was taken as 100%.