Project description:Many genes determining cell identity are regulated by clusters of Mediator-bound enhancer elements collectively referred to as super-enhancers. These super-enhancers have been proposed to manifest higher-order properties important in development and disease. Here we report a comprehensive functional dissection of one of the strongest putative super-enhancers in erythroid cells. By generating a series of mouse models, deleting each of the five regulatory elements of the α-globin super-enhancer individually and in informative combinations, we demonstrate that each constituent enhancer seems to act independently and in an additive fashion with respect to hematological phenotype, gene expression, chromatin structure and chromosome conformation, without clear evidence of synergistic or higher-order effects. Our study highlights the importance of functional genetic analyses for the identification of new concepts in transcriptional regulation.
Project description:Many genes determining cell identity are regulated by clusters of Mediator-bound enhancer elements collectively referred to as super-enhancers. These super-enhancers have been proposed to manifest higher-order properties important in development and disease. Here we report a comprehensive functional dissection of one of the strongest putative super-enhancers in erythroid cells. By generating a series of mouse models, deleting each of the five regulatory elements of the α-globin super-enhancer individually and in informative combinations, we demonstrate that each constituent enhancer seems to act independently and in an additive fashion with respect to hematological phenotype, gene expression, chromatin structure and chromosome conformation, without clear evidence of synergistic or higher-order effects. Our study highlights the importance of functional genetic analyses for the identification of new concepts in transcriptional regulation.
Project description:Many genes determining cell identity are regulated by a set of enhancer elements collectively referred to as super-enhancers. It has been suggested that super-enhancers represent a new class of cis-element, in which the assembly of enhancers confers an emergent property from the extended regulatory domain. To investigate this, we used published criteria to define one of the strongest super-enhancers in mouse erythroid cells – a 24kb region regulating α-globin expression, which comprises five enhancer-like components. Using homologous recombination, we deleted each component of this super-enhancer, singly and in informative combinations, and examined hematologic phenotype, gene expression, chromatin structure and chromosome conformation. Each component behaves independently, in an additive rather than synergistic manner. We conclude that the sub-classification of enhancers is unjustified beyond a description of their strength, which is defined by the number of lineage-specific transcription factors they bind. These findings ask afresh why enhancer-like elements cluster at key genes.
Project description:Many genes determining cell identity are regulated by a set of enhancer elements collectively referred to as super-enhancers. It has been suggested that super-enhancers represent a new class of cis-element, in which the assembly of enhancers confers an emergent property from the extended regulatory domain. To investigate this, we used published criteria to define one of the strongest super-enhancers in mouse erythroid cells – a 24kb region regulating α-globin expression, which comprises five enhancer-like components. Using homologous recombination, we deleted each component of this super-enhancer, singly and in informative combinations, and examined hematologic phenotype, gene expression, chromatin structure and chromosome conformation. Each component behaves independently, in an additive rather than synergistic manner. We conclude that the sub-classification of enhancers is unjustified beyond a description of their strength, which is defined by the number of lineage-specific transcription factors they bind. These findings ask afresh why enhancer-like elements cluster at key genes.
Project description:Many genes determining cell identity are regulated by a set of enhancer elements collectively referred to as super-enhancers. It has been suggested that super-enhancers represent a new class of cis-element, in which the assembly of enhancers confers an emergent property from the extended regulatory domain. To investigate this, we used published criteria to define one of the strongest super-enhancers in mouse erythroid cells – a 24kb region regulating α-globin expression, which comprises five enhancer-like components. Using homologous recombination, we deleted each component of this super-enhancer, singly and in informative combinations, and examined hematologic phenotype, gene expression, chromatin structure and chromosome conformation. Each component behaves independently, in an additive rather than synergistic manner. We conclude that the sub-classification of enhancers is unjustified beyond a description of their strength, which is defined by the number of lineage-specific transcription factors they bind. These findings ask afresh why enhancer-like elements cluster at key genes.
Project description:Haemoglobin, the oxygen-carrying molecule of red blood cells, at all stages of development comprises a tetramer of two α-like and two β-like globin chains. In humans and mice the highly conserved α- and β-globin loci contain genes encoding globin chains specifically expressed only during the first trimester of gestation (termed embryonic globins) in addition to the genes encoding globin chains expressed throughout adult life. In humans the β-globin locus also encodes a β-like chain that is expressed throughout the second and third trimesters of development; this is termed γ-globin and complexes with α-globin to form fetal haemoglobin (HbF). The sequential activation and repression of the genes at each of these loci throughout development to maturity is termed haemoglobin switching and is a poorly understood process. α-thalassemia, which results from insufficient production of α-globin, is a major global health problem with several hundred thousand sufferers world-wide. The embryonically expressed ζ-globin, encoded by the gene HBZ (Hba-x in mice), can functionally substitute for α-globin in adult erythroid cells. Reactivation of this gene is consequently likely to ameliorate the symptoms of α-thalassemia in individuals with a severe phenotype. Little is currently known about the regulation of ζ-globin expression in terms of both the trans- and cis-acting regulatory elements responsible for high-levels of expression of this gene during embryonic erythropoiesis and its maintenance in a transcriptionally inactive state throughout adult life. Using ATACseq and NG Capture C and mutant mouse lines this work aims to identify and define the cis-acting regulatory network underlying zeta-globin expression, and define the contribution of each regulatory element.
Project description:Haemoglobin, the oxygen-carrying molecule of red blood cells, at all stages of development comprises a tetramer of two α-like and two β-like globin chains. In humans and mice the highly conserved α- and β-globin loci contain genes encoding globin chains specifically expressed only during the first trimester of gestation (termed embryonic globins) in addition to the genes encoding globin chains expressed throughout adult life. In humans the β-globin locus also encodes a β-like chain that is expressed throughout the second and third trimesters of development; this is termed γ-globin and complexes with α-globin to form fetal haemoglobin (HbF). The sequential activation and repression of the genes at each of these loci throughout development to maturity is termed haemoglobin switching and is a poorly understood process. α-thalassemia, which results from insufficient production of α-globin, is a major global health problem with several hundred thousand sufferers world-wide. The embryonically expressed ζ-globin, encoded by the gene HBZ (Hba-x in mice), can functionally substitute for α-globin in adult erythroid cells. Reactivation of this gene is consequently likely to ameliorate the symptoms of α-thalassemia in individuals with a severe phenotype. Little is currently known about the regulation of ζ-globin expression in terms of both the trans- and cis-acting regulatory elements responsible for high-levels of expression of this gene during embryonic erythropoiesis and its maintenance in a transcriptionally inactive state throughout adult life. Using ATACseq and NG Capture C and mutant mouse lines this work aims to identify and define the cis-acting regulatory network underlying zeta-globin expression, and define the contribution of each regulatory element.