The composition of haemoglobin is modulated throughout early human development to produce proteins optimised for the unique oxygen requirements at each developmental stage. Regulation of the component α- and β-like globin proteins is carried out at the transcriptional level, with a single gene predominantly transcribed from each the α- and β-globin loci at any time. This regulation involves the coordinated action of activating and repressing transcription factors, which together work to direct the locus control region to drive expression of the appropriate genes. Efforts to understand this developmental switching process have been driven by the discovery that hereditary persistence of foetal haemoglobin (HPFH), a benign condition where the foetal γ-globin gene is abnormally expressed in adulthood, is associated with improved outcomes for patients who also suffer β-haemoglobinopathies, thus presenting an attractive therapeutic target for these diseases.
While many of the transcription factors involved in haemoglobin switching are known, some pieces of the puzzle are still missing. The transcription factor binding alterations caused by some of the HPFH mutations remain poorly understood. Identifying these novel factors and their interactions with transcriptional machinery is important to forming a comprehensive picture of the haemoglobin switching process.
Genomic locus proteomics (GLoPro) is a new technique that combines the precise targeting capabilities of CRISPR with promiscuous biotin labelling by an engineered APEX2 protein, allowing the capture of proteins located within the vicinity of a genetic region of interest. By directing this technology towards the β-globin locus, we hope to reveal new components of the molecular machinery used to regulate the haemoglobin switch, allowing a greater understanding of how these components collectively coordinate the switch. Completing the puzzle of haemoglobin switching will not only extend our knowledge of gene regulation at this archetypal locus, but may also yield desirable new therapeutic targets for the β-haemoglobinopathies.