An embryonic-specific repressor element located 3′ to the Aγ-globin gene influences transcription of the human β-globin locus in transgenic mice

Objective Persistent expression of the human fetal γ-globin genes in the adult stage is often associated with naturally occurring deletions in the human β-globin locus. The mapping of the 5′ breakpoints of these deletions within the Aγ- to δ-globin intergenic region has suggested that regulatory elements involved in the silencing of the γ-globin genes in the adult may be present. We previously identified two elements in this region, termed Enh and F, located 3′ to the Aγ-globin gene acting as silencers in transient transfection assays. Here, we tested directly the in vivo significance of these elements in the developmental regulation of the human β-like globin genes. Materials and methods We selectively deleted both Enh and F elements in the context of a 185-kb human β-globin locus PAC (P1 phage artificial chromosome) and tested the effects of this deletion on the expression of the human β-like globin genes in transgenic mice. Results The Enh/F deletion resulted in an increase in ε- and γ-globin mRNA levels in the embryonic yolk sac stage of erythropoiesis, which appears to be due to an increase in the rate of transcription rather than to an increase in the number of cells transcribing the human globin locus. However, the human developmental switching from fetal γ-globin to adult β-globin gene expression in transgenic mice was not affected by this deletion. Conclusion These results identify Enh and F as locus-wide regulatory elements capable of down-regulating transcription of the human β-globin locus in an embryonic-specific manner.