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:Transcriptional enhancers regulate gene expression in a developmental-stage and cell-specific manner. They were originally defined as individual regulatory elements that activate expression regardless of distance and orientation to their cognate genes. Genome-wide studies have shown that the mammalian enhancer landscape is much more complex, with different classes of individual enhancers and clusters of enhancer-like elements combining in additive, synergistic and redundant manners, possibly acting as single, integrated regulatory elements. These so-called super-enhancers are largely defined as clusters of enhancer-like elements which recruit particularly high levels of Mediator and often drive high levels of expression of key lineage-specific genes. Here, we analysed 78 erythroid-specific super-enhancers and showed that, as units, they preferentially interact in a directional manner, to drive expression of their cognate genes. Using the well characterised a-globin super-enhancer, we show that inverting this entire structure severely downregulates a-globin expression and activates flanking genes 5’ of the super-enhancer. Our detailed genetic dissection of the a-globin locus clearly attributes the cluster’s functional directionality to its sequence orientation, demonstrating that, unlike regular enhancers, super-enhancers act in an orientation-dependent manner. Together, these findings identify a novel emergent property of super-enhancers and revise current models by which enhancers are thought to contact and activate their cognate genes.
Project description:Transcriptional enhancers regulate gene expression in a developmental-stage and cell-specific manner. They were originally defined as individual regulatory elements that activate expression regardless of distance and orientation to their cognate genes. Genome-wide studies have shown that the mammalian enhancer landscape is much more complex, with different classes of individual enhancers and clusters of enhancer-like elements combining in additive, synergistic and redundant manners, possibly acting as single, integrated regulatory elements. These so-called super-enhancers are largely defined as clusters of enhancer-like elements which recruit particularly high levels of Mediator and often drive high levels of expression of key lineage-specific genes. Here, we analysed 78 erythroid-specific super-enhancers and showed that, as units, they preferentially interact in a directional manner, to drive expression of their cognate genes. Using the well characterised a-globin super-enhancer, we show that inverting this entire structure severely downregulates a-globin expression and activates flanking genes 5’ of the super-enhancer. Our detailed genetic dissection of the a-globin locus clearly attributes the cluster’s functional directionality to its sequence orientation, demonstrating that, unlike regular enhancers, super-enhancers act in an orientation-dependent manner. Together, these findings identify a novel emergent property of super-enhancers and revise current models by which enhancers are thought to contact and activate their cognate genes.
Project description:Transcriptional enhancers regulate gene expression in a developmental-stage and cell-specific manner. They were originally defined as individual regulatory elements that activate expression regardless of distance and orientation to their cognate genes. Genome-wide studies have shown that the mammalian enhancer landscape is much more complex, with different classes of individual enhancers and clusters of enhancer-like elements combining in additive, synergistic and redundant manners, possibly acting as single, integrated regulatory elements. These so-called super-enhancers are largely defined as clusters of enhancer-like elements which recruit particularly high levels of Mediator and often drive high levels of expression of key lineage-specific genes. Here, we analysed 78 erythroid-specific super-enhancers and showed that, as units, they preferentially interact in a directional manner, to drive expression of their cognate genes. Using the well characterised a-globin super-enhancer, we show that inverting this entire structure severely downregulates a-globin expression and activates flanking genes 5’ of the super-enhancer. Our detailed genetic dissection of the a-globin locus clearly attributes the cluster’s functional directionality to its sequence orientation, demonstrating that, unlike regular enhancers, super-enhancers act in an orientation-dependent manner. Together, these findings identify a novel emergent property of super-enhancers and revise current models by which enhancers are thought to contact and activate their cognate genes.