Human Fetal Globin Gene Expressed In Adulthood Continued Study Of The Mechanism

The human p-globin locus contains five functional genes in the order 5'-ε-Gγ-Aγ-δ-β-3'. During ontogeny, expression of these genes undergoes two developmental switches, from embryonic (ε) to fetal (Gγ and Aγ) during the early gestational period and from fetal to adult (δ and β) during the perinatal period. At present, the molecular mechanisms of the hemoglobin switching remain unclearly. The human γ-globin genes express mainly in the fetal liver and their products become less than 1% of the total β-like globin chains in adult erythroid cells. However, naturally occurring deletion or point mutations within the β-globin gene cluster may interfere with the fetal-to-adult switching and result in the expression of the γ-globin genes persisting at high levels in adults. These natural mutants have provided favorite molecular models for the study of the mechanisms of hemoglobin switching. Additionally, the increase of fetal hemoglobin (HbF, α₂γ₂) can ameliorate the clinical symptoms of inherited abnormalities of β-globin gene expression, such as β-thalassemia and sickle cell anemia. The investigations of these natural mutants may contribute to elucidation of the mechanisms of hemoglobin switching as well as provide certain strategies for gene therapy of β-thalassemia and sickle cell anemia.We have identified a novel AγHPFH heterozygote who has a high level of HbF (23.8%) with dominant Ay type (Aγ/(Gγ+Aγ)=83%) and normal level of HbA₂ (α₂δ₂, 3.0%). She has no obvious anemia (Hb=11.5g/dl, MCV=84.1fl, MCH=26.1pg). We mapped the β-globin gene cluster and detected no obvious DNA rearrangement and deletion within it. Direct sequencing analysis of her Gγ- and Aγ-globin gene promoters obtained by PCR showed that the Gγ-globin gene promoter was normal but a novel T→C substitution occurred at -173 of the Aγ-globin gene. We further cloned the amplified Aγ-globin gene promoter into the pGEM-4Z vector and performed sequencing analysis. It was...