βH1-globin expression in fetal liver definitive erythroid cells. (A) Levels of εy-, βH1-, and β1-globin transcripts were determined by qPCR and graphed as a percentage of total β-globin transcripts. Circulating E11.5 primitive erythroid cells (PB) express high levels of εy- and βH1-globin. Proerythroblasts (Ter119^lo, c-kit⁺) from late fetal liver and adult BM express β1-globin and no embryonic globins. While E11.5 liver proerythroblasts express a unique combination of β-globins with both βH1- and β1- but little if any εy-globin. Error bars are SEM of 3 samples. (B) RNA Pol II occupancy at the β-globin locus was determined by ChIP. The murine β-globin locus is depicted to scale above the graph with the probes used indicated by short dashes. Significantly higher levels of RNA Pol II were found associated the βH1-globin promoter than the εy-globin promoter in E11.5 fetal liver cells (P < .007) based on 1-way ANOVA analysis. Error bars represent SEM of 3 samples.