Project description:FACT mediates cohesin function on chromatin Cohesin is a key regulator of genome architecture with roles in sister chromatid cohesion and the organisation of higher-order structures during interphase and mitosis. The recruitment and mobility of cohesin complexes on DNA are restricted by nucleosomes. Here we show that cohesin role in chromosome organization requires the histone chaperone FACT. Depletion of FACT in metaphase cells affects cohesin stability on chromatin reducing its accumulation at pericentric regions and binding on chromosome arms. Using Hi-C, we show that cohesin-dependent TAD (Topological Associated Domains)-like structures in G1 and metaphase chromosomes are disrupted in the absence of FACT. Surprisingly, sister chromatid cohesion is intact in FACT-depleted cells, although chromosome segregation failure is observed. Our results uncover a role for FACT in genome organisation by facilitating cohesin dependent compartmentalization of chromosomes into loop domains.
Project description:Cohesin is a key regulator of genome architecture with roles in sister chromatid cohesion and the organisation of higher-order structures during interphase and mitosis. The recruitment and mobility of cohesin complexes on DNA are restricted by nucleosomes. Here we show that cohesin role in chromosome organization requires the histone chaperone FACT. Depletion of FACT in metaphase cells affects cohesin stability on chromatin reducing its accumulation at pericentric regions and binding on chromosome arms. Using Hi-C, we show that cohesin-dependent TAD (Topological Associated Domains)-like structures in G1 and metaphase chromosomes are disrupted in the absence of FACT. Surprisingly, sister chromatid cohesion is intact in FACT-depleted cells, although chromosome segregation failure is observed. Our results uncover a role for FACT in genome organisation by facilitating cohesin dependent compartmentalization of chromosomes into loop domains.
Project description:Catalytic activity of the ISWI family of remodelers is critical for nucleosomal organization and transcription factor binding, including the insulator protein CTCF. To define which subcomplex mediates these diverse functions we phenotyped a panel of isogenic mouse stem cell lines each lacking one of six ISWI accessory subunits. Individual deletions of either CERF, RSF1, ACF, WICH or NoRC subcomplexes only moderately affect the chromatin landscape, while removal of the NURF-specific subunit BPTF leads to drastic reduction in chromatin accessibility and Snf2h ATPase localization around CTCF sites. While this reduces distances to the adjacent nucleosomes it only modestly impacts CTCF binding itself. In absence of accessibility, the insulator function of CTCF is nevertheless impaired resulting in lower occupancy of cohesin and cohesin-loading factors, and reduced insulation at these sites, highlighting the need of NURF-mediated remodeling for open chromatin and proper CTCF function. Our comprehensive analysis reveals a specific role for NURF in mediating Snf2h localization and chromatin opening at bound CTCF sites showing that local accessibility is critical for cohesin binding and insulator function.
Project description:Cohesin mediates sister chromatid cohesion and organizes the genome through the formation of chromatin loops. Two versions of the complex carrying either STAG1 or STAG2 show overlapping and specific functions and both are required to fulfill embryonic development. Cohesin-STAG1 displays longer residence time on chromatin that depends on CTCF and ESCO1 and establishes longer, long-lived chromatin loops together with CTCF. Cohesin-STAG2 shows a preferential interaction with WAPL and mediates shorter loops involved in tissue-specific transcription independently of CTCF. Here we show that the two variants respond in opposite ways to knock down of NIPBL, the putative cohesin loader that is also essential for loop extrusion. Cohesin-STAG1 levels increase on chromatin under this condition and the complex accumulates further at CTCF positions while cohesin-STAG2 is diminished genome-wide. Our data support a model in which NIPBL is not required for association of cohesin with chromatin but it is for loop extrusion, which in turn facilitates stabilization of cohesin-STAG2 at CTCF positions after being loaded elsewhere. In contrast, cohesin-STAG1 is preferentially loaded at CTCF sites independently of NIPBL. Nevertheless, loop formation by these chromatin-bound complexes is impaired and gene expression is severely affected, resembling alterations in Cornelia de Lange patients
Project description:Cohesin complex members have recently been identified as putative tumor suppressors in hematologic and epithelial malignancies. The cohesin complex guides chromosome segregation, however cohesin-mutant leukemias do not show genomic instability. We hypothesized reduced cohesin function alters chromatin structure and disrupts cis-regulatory architecture of hematopoietic progenitors. We investigated the consequences of Smc3 deletion in normal and malignant hematopoiesis. Bi-allelic Smc3 loss induced bone marrow aplasia with premature sister chromatid separation, and revealed an absolute requirement for cohesin in hematopoietic stem cell function. In contrast, Smc3 haploinsufficiency increased self-renewal in vitro and in vivo including competitive transplantation. Smc3 haploinsufficiency reduced coordinated transcriptional output, including reduced expression of transcription factors and other genes associated with lineage commitment. Smc3 haploinsufficiency cooperated with Flt3-ITD to induce acute leukemia in vivo, with potentiated Stat5 signaling and altered nucleolar topology. These data establish a dose-dependency for cohesin in regulating chromatin structure and hematopoietic stem cell function. ATAC-seq in murine c-kit+ cells for the following genotypes: Smc3 fl/+, Smc3 del/+, Flt3-ITD, Smc3 fl/del Flt3-ITD
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:The DEMETER (DME) DNA glycosylase mediates genome-wide DNA demethylation and is required for endosperm genomic imprinting and embryo viability. Targets of DME-demethylation are small, AT-rich transposons and boundaries of large heterochromatic transposons, but how DME interacts with chromatin is unclear. To investigate the interaction between DME and chromatin, we analyzed DNA methylation in Arabidopsis seeds and pollen deficient in the chromatin remodeler FAcilitates Chromatin Transactions (FACT) complex. We find that FACT co-localizes with nuclear DME, and is required for DME activity in chromatin domains with high nucleosome occupancy and histone modifications associated with heterochromatin, which comprise over half of DME target loci. We also demonstrate that heterochromatin-associated linker histone H1 mediates the requirement for FACT at a subset of DME-target loci. However, FACT is not required for DME demethylation of targets in euchromatic regions. Thus, chromatin structure determines the degree to which FACT facilitates access of DME to its targets.
Project description:Cohesin mediates sister chromatid cohesion and organizes the genome through the formation of chromatin loops. Two versions of the complex carrying either STAG1 or STAG2 show overlapping and specific functions and both are required to fulfill embryonic development. Cohesin-STAG1 displays longer residence time on chromatin that depends on CTCF and ESCO1 and establishes longer, long-lived chromatin loops together with CTCF. Cohesin-STAG2 shows a preferential interaction with WAPL and mediates shorter loops involved in tissue-specific transcription independently of CTCF. Here we show that the two variants respond in opposite ways to knock down of NIPBL, the putative cohesin loader that is also essential for loop extrusion. Cohesin-STAG1 levels increase on chromatin under this condition and the complex accumulates further at CTCF positions while cohesin-STAG2 is diminished genome-wide. Our data support a model in which NIPBL is not required for association of cohesin with chromatin but it is for loop extrusion, which in turn facilitates stabilization of cohesin-STAG2 at CTCF positions after being loaded elsewhere. In contrast, cohesin-STAG1 is preferentially loaded at CTCF sites independently of NIPBL. Nevertheless, loop formation by these chromatin-bound complexes is impaired and gene expression is severely affected, resembling alterations in Cornelia de Lange patients
Project description:Cohesin mediates sister chromatid cohesion and organizes the genome through the formation of chromatin loops. Two versions of the complex carrying either STAG1 or STAG2 show overlapping and specific functions and both are required to fulfill embryonic development. Cohesin-STAG1 displays longer residence time on chromatin that depends on CTCF and ESCO1 and establishes longer, long-lived chromatin loops together with CTCF. Cohesin-STAG2 shows a preferential interaction with WAPL and mediates shorter loops involved in tissue-specific transcription independently of CTCF. Here we show that the two variants respond in opposite ways to knock down of NIPBL, the putative cohesin loader that is also essential for loop extrusion. Cohesin-STAG1 levels increase on chromatin under this condition and the complex accumulates further at CTCF positions while cohesin-STAG2 is diminished genome-wide. Our data support a model in which NIPBL is not required for association of cohesin with chromatin but it is for loop extrusion, which in turn facilitates stabilization of cohesin-STAG2 at CTCF positions after being loaded elsewhere. In contrast, cohesin-STAG1 is preferentially loaded at CTCF sites independently of NIPBL. Nevertheless, loop formation by these chromatin-bound complexes is impaired and gene expression is severely affected, resembling alterations in Cornelia de Lange patients