Persistent γ-globin expression in adult transgenic mice after selective removal of the two embryonic-specific repressor element located 3’ to the Aγ-globin gene

Natural deletions of the human β-globin gene cluster lead to specific syndromes characterized by increased production of fetal hemoglobin in adult life and provide a useful model to delineate novel cis-acting elements involved in the developmental control of hemoglobin switching. A hypothesis accounting for these phenotypic features, assumes that silencers located within the Aγ to δ-gene region, are deleted in hereditary persistence of fetal hemoglobin (HPFH) and δβ-thalassemias, leading to failure of switching. In the present study, we sought to clarify the in vivo role of two elements, termed Enh and F, located 3' to the Aγ-globin in silencing the fetal genes. To this end, we generated three transgenic lines using cosmid constructs containing the full length of the globin locus control region (LCR) linked to the 3.3 kb Aγ-gene, lacking both the Enh and F elements. The Enh/F deletion resulted in high levels of Aγ-globin gene expression in adult mice, in all single copy lines, whereas, the LCRAγ single copy lines which retain the Enh and F elements, exhibited complete normal switching of the fetal Aγ-gene. Our study documents directly for the first time the in vivo role of these two gene-proximal negative regulatory elements in silencing the fetal globin gene in the perinatal period and thus these data may permit their eventual exploitation in therapeutic approaches for thalassemias. MeSH-Medline key Words: Gene regulation; Locus control region (LCR); Hemoglobin switching; Thalassemias; Hereditary persistence of fetal hemoglobin (HPFH) U N C O R R E C TE D P R O O F Molecular Medicine