The regulation of globin gene expression during haematopoiesis

We now have an approximate map of the DNA sequence for the entire human genome. However the basic DNA sequence is only a starting block for understanding the complex interplay of factors which regulate the ability of a gene to make the correct protein at the correct time and in the correct cell type. We have a very detailed map of a region of chromosome 16. We want to characterise this region by identifying all the genes and regulatory features within the sequence, and then to look at additional (epigenetic) factors which can influence when and where a gene becomes active. DNA coils down within a cell nucleus with several proteins to form chromatin. We would like to understand how this chromatin is arranged within a nucleus and what changes may be necessary to allow genes to be switched on or off. Within this region of chromosome 16 lie the alpha globin genes. These genes make part of the molecule haemoglobin which carries oxygen in the blood and lack of haemoglobin will give rise to anaemia, which can cause malfunctions in the organs normally supplied with oxygen. When the alpha globin genes are disrupted in some way, patients develop a severe form of anaemia called alpha thalassaemia. Some patients are born with mental retardation and other developmental problems as well as alpha thalassaemia - these patients have a piece of chromosome 16 missing from the region we are studying. With the information from our mapping work and studies of nuclear organisation, we will identify precisely which genes are missing in these patients and how that loss contributes to their mental and developmental difficulties.

Now that DNA sequence is available for many mammalian genomes, recent studies have focused on genome-wide approaches to determine how the key elements are organized; how this relates to nuclear function (including DNA replication, recombination and repair, DNA transcription and RNA processing), and how these processes are influenced by interactions with epigenetic phenomena (nuclear position, timing of replication, chromatin modifications and DNA modifications by methylation and hydroxymethylation). In future we plan to use such approaches to analyse how genes are regulated during haematopoiesis and particularly in erythropoiesis. Valuable as this ‘big picture’ is, it is critical that the generalities it produces are assessed for their accuracy by examination of individual loci whose detailed structure and many natural variants have been determined, and whose function can be verified by experimental manipulation. The ? globin locus and the surrounding region is one of the best characterised segments of the genome (in mouse and human) and therefore is ideal for testing predictions from the genome-wide studies. Equally, we will continue to test predictions made about nuclear processes from detailed analysis of this region by genome-wide studies. The ultimate goal of this work is to develop new ways to modify gene expression during erythropoiesis with the aim of manipulating globin gene expression and ameliorating the clinical phenotypes of patients with thalassaemia.