Functional investigation of the hbs1l-myb intergenic region on chromosome 6q

Abstract

Fetal haemoglobin levels have a major impact on the severity of sickle cell disease (SCD) and Beta-Thalassaemia. Previous studies by our group shows that three loci – the HBS1L-MYB intergenic region (HMIP) on chromosome 6q23, BCL11A on chromosome 2p16 and the β globin cluster on chromosome 11 accounts for up to 50 % of the variation in HbF levels in non-anaemic Europeans. Recent work by our group indicated the presence of regulatory elements in HBS1L-MYB intergenic region (HMIP) evidenced by GATA-1 binding coinciding with strong histone acetylation, RNA polymerase II activity, and erythroid specific DNase I hypersensitive sites. Genetic studies and resequencing of two key individuals from the family that led to discovery of 6q QTL revealed new SNPs in the HBS1L-MYB intergenic region.
In silico predictions suggested that a couple of these SNPs altered binding of key transcription factors. We proposed that differential binding of these transcription factors mediated through these SNPs underlie the association with HbF control.
Electrophoretic Mobility Shift Assays (EMSAs) and Chromatin immunoprecipitation followed by real time PCR (ChIP-qPCR) and HaploChIP showed that many of the genetically associated variants altered the binding of key transcription factors such as GATA-1, KLF1 and MYB that have crucial roles in globin regulation as well as regulation of erythropoiesis.
We have also compared ex-vivo erythroid cell culture kinetics and expression profiles of individuals who are homozygous for the presence or absence of the allelic variant associated with HbF. MYB expression and maturation rate of erythroblasts were noticeably different whereas expression of HBS1L the other flanking gene was not different. We could also demonstrate unequal expression of MYB in individuals heterozygous for the HMIP variants but the direction of the effect should be further investigated.
These results further support the regulatory role of HBS1L-MYB intergenic polymorphisms on HbF and erythropoietic kinetics supporting our hypothesis that the effect of the intergenic SNPs is indirect via the flanking MYB gene.

Date of Award	2014
Original language	English
Awarding Institution	King's College London
Supervisor	Swee Lay Thein (Supervisor) & Steven Best (Supervisor)