Mutations in the adult β-globin gene disrupt the normal function of haemoglobin, the oxygen carrying protein found in red blood cells. This leads to genetic disorders termed β-haemoglobinopathies, such as sickle cell anaemia and β-thalassemia. The number of infants born with β-haemoglobinopathies has been rising annually as the populations across areas with high carrier rates have grown. There is an ongoing need for more effective long-term treatments.
Reactivation of the silenced foetal γ-globin genes can compensate for dysfunctional adult β-globin and alleviates symptoms. One strategy towards reactivating the foetal γ-globin genes is to interfere with the mechanisms of repression. We have shown that the Zinc Finger and BTB Domain Containing 7A (ZBTB7A) acts by binding to the -200 proximal promoter site and directly represses foetal globin expression. However, the details of how it regulates γ-globin expression and whether there are other functional binding sites in the β-globin locus was unknown.
Using ZBTB7A ChIP-seq data and gel-based assays, we have mapped ZBTB7A binding sites within the β-globin locus. We have introduced mutations using CRISPR-Cas9 genome editing at selected sites to determine their functional importance in foetal globin repression. Since ZBTB7A can self-associate via its POZ domain we hypothesise that it coordinates long range chromatin contacts. We are investigating a model whereby ZBTB7A may bind at multiple sites across the locus to ensure the appropriate 3D topology, including looping of the power Locus Control Region enhancer to individual globin gene promoters.