The hemoglobin regulatory regions

All animals that use hemoglobin for oxygen transport synthesize different hemoglobin types during the various stages of development. In humans, two gene clusters direct the production of hemoglobin including the α-locus which contains the embryonic ζ gene and two adult α genes on chromosome 16. A second cluster, the β-globin locus located on chromosome 11, contains the ε, ^Gγ, ^Aγ, δ, and β genes. The globin genes are arranged from 5′ to 3′ according to the order of their expression and are developmentally regulated to produce different hemoglobin species during ontogeny. Two switches in the type of hemoglobin synthesized during development occur, a process known as hemoglobin switching. Through research efforts over the last two decades, several insights have been gained into the molecular mechanisms of hemoglobin switching. However, the entire process has not been fully elucidated. Studies of naturally occurring globin gene promoter mutations and transgenic mouse investigations have contributed to our understanding of the effect of DNA mutations on globin gene expression. Furthermore, the developmental regulation of globin gene expression has shaped research efforts to establish therapeutic modalities for individuals affected with sickle cell disease and β-thalassemia. Here, we will review the progress made toward understanding molecular mechanisms that control globin gene expression and the consequences of mutations on hemoglobin switching.