Project description:Mammalian genomes contain several billion base pairs of DNA which are packaged in chromatin fibers. At selected gene loci, cohesin complexes have been proposed to arrange chromatin fibers into higher-order structures, but it is poorly understood how cohesin performs this task, how important this function is for determining the structure of chromosomes, and how this process is regulated to allow changes in gene expression. Here we show that the cohesin release factor Wapl controls chromatin structure and gene regulation at numerous loci throughout the mouse genome. Conditional deletion of the Wapl gene leads to stable accumulation of cohesin on chromatin, chromatin compaction, altered gene expression, cell cycle delay, chromosome segregation defects and embryonic lethality. In Wapl deficient chromosomes, cohesin accumulates in an axial domain, similar to how condensins form a M-bM-^@M-^\scaffoldM-bM-^@M-^] in mitotic chromosomes. We propose that Wapl controls chromatin structure and gene regulation by determining the residence time with which cohesin binds to DNA. 4 biological replicates for each genotype (Wapl +/F; Wapl -/F) treated with/without 4-OHT =16 samples
Project description:Mammalian genomes contain several billion base pairs of DNA which are packaged in chromatin fibers. At selected gene loci, cohesin complexes have been proposed to arrange chromatin fibers into higher-order structures, but it is poorly understood how cohesin performs this task, how important this function is for determining the structure of chromosomes, and how this process is regulated to allow changes in gene expression. Here we show that the cohesin release factor Wapl controls chromatin structure and gene regulation at numerous loci throughout the mouse genome. Conditional deletion of the Wapl gene leads to stable accumulation of cohesin on chromatin, chromatin compaction, altered gene expression, cell cycle delay, chromosome segregation defects and embryonic lethality. In Wapl deficient chromosomes, cohesin accumulates in an axial domain, similar to how condensins form a “scaffold” in mitotic chromosomes. We propose that Wapl controls chromatin structure and gene regulation by determining the residence time with which cohesin binds to DNA. ChIP-Seq using two different antibodies (CTCF, Smc3); one (CTCF) and two (Smc3) replicates; two different genotypes (Wapl +/delta, Wapl -/delta). The control sample is a single-replicate INPUT for each genotype.
Project description:Mammalian genomes contain several billion base pairs of DNA which are packaged in chromatin fibers. At selected gene loci, cohesin complexes have been proposed to arrange chromatin fibers into higher-order structures, but it is poorly understood how cohesin performs this task, how important this function is for determining the structure of chromosomes, and how this process is regulated to allow changes in gene expression. Here we show that the cohesin release factor Wapl controls chromatin structure and gene regulation at numerous loci throughout the mouse genome. Conditional deletion of the Wapl gene leads to stable accumulation of cohesin on chromatin, chromatin compaction, altered gene expression, cell cycle delay, chromosome segregation defects and embryonic lethality. In Wapl deficient chromosomes, cohesin accumulates in an axial domain, similar to how condensins form a “scaffold” in mitotic chromosomes. We propose that Wapl controls chromatin structure and gene regulation by determining the residence time with which cohesin binds to DNA.
Project description:Mammalian genomes contain several billion base pairs of DNA which are packaged in chromatin fibers. At selected gene loci, cohesin complexes have been proposed to arrange chromatin fibers into higher-order structures, but it is poorly understood how cohesin performs this task, how important this function is for determining the structure of chromosomes, and how this process is regulated to allow changes in gene expression. Here we show that the cohesin release factor Wapl controls chromatin structure and gene regulation at numerous loci throughout the mouse genome. Conditional deletion of the Wapl gene leads to stable accumulation of cohesin on chromatin, chromatin compaction, altered gene expression, cell cycle delay, chromosome segregation defects and embryonic lethality. In Wapl deficient chromosomes, cohesin accumulates in an axial domain, similar to how condensins form a “scaffold” in mitotic chromosomes. We propose that Wapl controls chromatin structure and gene regulation by determining the residence time with which cohesin binds to DNA.
Project description:The structure of the higher-order chromatin fiber has not been defined in detail. We have used a novel approach based on sucrose gradient centrifugation to compare the conformation of centromeric satellite DNA-containing higher-order chromatin fibers with bulk chromatin fibers obtained from the same mouse fibroblast cells. Our data show that chromatin fibers derived from the centromeric domain of a chromosome exist in a more condensed structure than bulk chromatin whereas pericentromeric chromatin fibers have an intermediate conformation. From the standpoint of current models, our data are interpreted to suggest that satellite chromatin adopts a regular helical conformation compatible with the canonical 30-nm chromatin fiber whereas bulk chromatin fibers appear less regularly folded and are perhaps intermittently interrupted by deformations. This distinctive conformation of the higher-order chromatin fiber in the centromeric domain of the mammalian chromosome could play a role in the formation of heterochromatin and in the determination of centromere identity.
Project description:HOX cluster genes are activated sequentially in their positional order along the chromosome during vertebrate development. This phenomenon, known as temporal colinearity, depends on transcriptional silencing of 5' HOX genes. Chromatin looping was recently identified as a conserved feature of silent HOX clusters, with CCCTC-binding factor (CTCF) binding sites located at the loop bases. However, the potential contribution of CTCF to HOX cluster silencing and the underlying mechanism have not been established. Here, we demonstrate that the HOXA locus is organized by CTCF into chromatin loops and that CTCF depletion causes significantly enhanced activation of HOXA3 to -A7, -A9 to -A11, and -A13 in response to retinoic acid, with the highest effect observed for HOXA9. Our subsequent analyses revealed that CTCF facilitates the stabilization of Polycomb repressive complex 2 (PRC2) and trimethylated lysine 27 of histone H3 (H3K27me3) at the human HOXA locus. Our results reveal that CTCF functions as a controller of HOXA cluster silencing and mediates PRC2-repressive higher-order chromatin structure.
Project description:Recent technological advances in the field of chromosome conformation capture are facilitating tremendous progress in the ability to map the three-dimensional (3D) organization of chromosomes at a resolution of several Kb and at the scale of complete genomes. Here we review progress in analyzing chromosome organization in human cells by building 3D models of chromatin based on comprehensive chromatin interaction datasets. We describe recent experiments that suggest that long-range interactions between active functional elements are sufficient to drive folding of local chromatin domains into compact globular states. We propose that chromatin globules are commonly formed along chromosomes, in a cell type specific pattern, as a result of frequent long-range interactions among active genes and nearby regulatory elements. Further, we speculate that increasingly longer range interactions can drive aggregation of groups of globular domains. This process would yield a compartmentalized chromosome conformation, consistent with recent observations obtained with genome-wide chromatin interaction mapping.