Cohesin Function Research Articles

Cohesin organizes 3D DNA contacts surrounding active enhancers in C. elegans.

In mammals, cohesin and CTCF organize the 3D genome into topologically associated domains (TADs) to regulate communication between cis-regulatory elements. Many organisms, including S. cerevisiae, C. elegans, and A. thaliana contain cohesin but lack CTCF. Here, we used C. elegans to investigate the function of cohesin in 3D genome organization in the absence of CTCF. Using Hi-C data, we observe cohesin-dependent features called "fountains", which are also reported in zebrafish and mice. These are population average reflections of DNA loops originating from distinct genomic regions and are ~20-40 kb in C. elegans. Hi-C analysis upon cohesin and WAPL depletion support the idea that cohesin is preferentially loaded at NIPBL occupied sites and loop extrudes in an effectively two-sided manner. ChIP-seq analyses show that cohesin translocation along the fountain trajectory depends on a fully intact complex and is extended upon WAPL-1 depletion. Hi-C contact patterns at individual fountains suggest that cohesin processivity is unequal on each side, possibly due to collision with cohesin loaded from surrounding sites. The putative cohesin loading sites are closest to active enhancers and fountain strength is associated with transcription. Compared to mammals, average processivity of C. elegans cohesin is ~10-fold shorter and NIPBL binding does not depend on cohesin. We propose that preferential loading and loop extrusion by cohesin is an evolutionarily conserved mechanism that regulates the 3D interactions of enhancers in animal genomes.

Cohesin composition and dosage independently affect early development in zebrafish.

Cohesin, a chromatin-associated protein complex with four core subunits (Smc1a, Smc3, Rad21 and either Stag1 or 2), has a central role in cell proliferation and gene expression in metazoans. Human developmental disorders termed 'cohesinopathies' are characterized by germline variants of cohesin or its regulators that do not entirely eliminate cohesin function. However, it is not clear whether mutations in individual cohesin subunits have independent developmental consequences. Here, we show that zebrafish rad21 or stag2b mutants independently influence embryonic tailbud development. Both mutants have altered mesoderm induction, but only homozygous or heterozygous rad21 mutation affects cell cycle gene expression. stag2b mutants have narrower notochords and reduced Wnt signaling in neuromesodermal progenitors as revealed by single-cell RNA sequencing. Stimulation of Wnt signaling rescues transcription and morphology in stag2b, but not rad21, mutants. Our results suggest that mutations altering the quantity versus composition of cohesin have independent developmental consequences, with implications for the understanding and management of cohesinopathies.

Cohesin Complex: Structure and Principles of Interaction with DNA.

Accurate duplication and separation of long linear genomic DNA molecules is associated with a number of purely mechanical problems. SMC complexes are key components of the cellular machinery that ensures decatenation of sister chromosomes and compaction of genomic DNA during division. Cohesin, one of the essential eukaryotic SMC complexes, has a typical ring structure with intersubunit pore through which DNA molecules can be threaded. Capacity of cohesin for such topological entrapment of DNA is crucial for the phenomenon of post-replicative association of sister chromatids better known as cohesion. Recently, it became apparent that cohesin and other SMC complexes are, in fact, motor proteins with a very peculiar movement pattern leading to formation of DNA loops. This specific process has been called loop extrusion. Extrusion underlies multiple functions of cohesin beyond cohesion, but molecular mechanism of the process remains a mystery. In this review, we summarized the data on molecular architecture of cohesin, effect of ATP hydrolysis cycle on this architecture, and known modes of cohesin-DNA interactions. Many of the seemingly disparate facts presented here will probably be incorporated in a unified mechanistic model of loop extrusion in the not-so-distant future.

PRAME induces genomic instability in uveal melanoma

PRAME is a CUL2 ubiquitin ligase subunit that is normally expressed in the testis but becomes aberrantly overexpressed in many cancer types in association with aneuploidy and metastasis. Here, we show that PRAME is expressed predominantly in spermatogonia around the time of meiotic crossing-over in coordination with genes mediating DNA double strand break repair. Expression of PRAME in somatic cells upregulates pathways involved in meiosis, chromosome segregation and DNA repair, and it leads to increased DNA double strand breaks, telomere dysfunction and aneuploidy in neoplastic and non-neoplastic cells. This effect is mediated at least in part by ubiquitination of SMC1A and altered cohesin function. PRAME expression renders cells susceptible to inhibition of PARP1/2, suggesting increased dependence on alternative base excision repair pathways. These findings reveal a distinct oncogenic function of PRAME that can be targeted therapeutically in cancer.

Stag2-Cohesin Loss Attenuates Flt3 ITD Myeloid Blast Expansion Yet Preserves Mutant HSC

FLT3 is mutated through an internal tandem duplication (ITD) in 20-25% of acute myeloid leukemia (AML), driving aberrant STAT5/AKT signaling and leukemogenesis. Murine modelling of ITD showed marked myeloid progenitor expansion and hematopoietic stem cell (HSC) exhaustion in various co-mutant settings. Here we present a Stag2 Δ Flt3 ITD model with stark reversal of these two aforementioned features. STAG2, a cohesin complex member, maintains the integrity of the 3D genome partitioning structure known as topologically structural domains. Loss of Stag2 impairs the access and engagement of key hematopoietic transcription factors such as PU.1 to their target genes. sAML is diagnosed when patients present leukemia with known history of hematological malignancies or chemotherapy/radiotherapy treatment. Comparing to de novo AML, sAML often arises in older patients and harbors a poor prognosis with a 5-year overall survival rate of <30%. Advances in genomic studies found various epigenetic mutations, such as STAG2, are often associated with sAML and AML-myelodysplastic related changes (MRC) subtype. STAG2 mutations are found in 14-20% of sAML cases and is suggested to reside within a dominant clone during the pre-leukemia phase, MDS to sAML transformation, such as with FLT3 ITD acquisition and persists during remission. To understand the mechanistic contribution of STAG2-cohesin loss with FLT3 ITD, we generated sequential mutagenesis murine models where the order of Stag2 and Flt3 ITD mutation is set as either ITD 1st Stag2 2nd ( de novo like) or Stag2 1stITD 2nd (sAML like) using tamoxifen-inducible Cre/Flpo recombinase or pIpC-inducible Mx1Cre. In the de novo like model, ITD is constitutively active then Stag2 is deleted when mice reach 6-8 weeks of age. Surprisingly, loss of Stag2 attenuates LSK to MP transition at 4 weeks post deletion, while MPP3 remains elevated, suggesting aberrant remodeling of myeloid differentiation. In the sAML like model, Stag2 is deleted via Mx1Cre and waited for 4 months to mimic the MDS phase, which is then followed by activation of ITD mutation via Flpo, which represents the MDS to sAML transformation. After activating both mutations, mice were followed for another 4 months before analyzing the hematopoietic stem and progenitor compartment. In contrast to the de novo like model, sequential Stag2 1stITD 2nd preserves the HSC population defined by either immunophenotyping or transcriptome via scRNAseq ( Figure 1). The mutant HSC is more quiescent but retains the capacity to reconstitute lethally irradiated recipients in the short term. Similar to the de novo like model, sequential Stag2 1stITD 2nd mice also exhibits a blocked myeloid differentiation. Comparing to ITD mutant, Stag2 1stITD 2nd LSK cells have decreased expression of Socs2 and Cish. While functionally determining the role of mutant HSC, we are performing RNA-seq during at early timepoints post ITD activation to determine how preceding Stag2 mutation could have altered the stem cell fate decision. Targeted therapy with inhibitors of FLT3 have had an overall survival benefit in FLT3-mutant AML, though the magnitude of effect has been modest. STAG2 mutations are more likely to be identified in poor responders to FLT3 inhibition as both reported by us with Pexidartinib treatment, as well as in the setting of Crenolanib treatment where expansion of the STAG2-mutant clone was observed during treatment. Thus, remodeling of the chromatin landscape though altered CTCF binding or cohesin function might impact leukemia identity in FLT3-mutant AML. Our data highlights an important regulatory role of Stag2-cohesin in Flt3 ITD mediated leukemogenesis, while generating a model that mimics the genetic evolution of sAML. This model will not only shed light on the sAML pathogenesis but also with creates a pre-clinical testing platform with potential therapeutic relevance.

BRWD1 orchestrates small pre-B cell chromatin topology by converting static to dynamic cohesin.

Lymphocyte development consists of sequential and mutually exclusive cell states of proliferative selection and antigen receptor gene recombination. Transitions between each state require large, coordinated changes in epigenetic landscapes and transcriptional programs. How this occurs remains unclear. Here we demonstrate that in small pre-B cells, the lineage and stage-specific epigenetic reader bromodomain and WD repeat-containing protein 1 (BRWD1) reorders three-dimensional chromatin topology to affect the transition between proliferative and gene recombination molecular programs. BRWD1 regulated the switch between poised and active enhancers interacting with promoters, and coordinated this switch with Igk locus contraction. BRWD1 did so by converting chromatin-bound static to dynamic cohesin competent to mediate long-range looping. ATP-depletion revealed cohesin conversion to be the main energetic mechanism dictating dynamic chromatin looping. Our findings provide a new mechanism of cohesin regulation and reveal how cohesin function can be dictated by lineage contextual mechanisms to facilitate specific cell fate transitions.

CRISPR screens in sister chromatid cohesion defective cells reveal PAXIP1-PAGR1 as regulator of chromatin association of cohesin.

The cohesin complex regulates higher order chromosome architecture through maintaining sister chromatid cohesion and folding chromatin by DNA loop extrusion. Impaired cohesin function underlies a heterogeneous group of genetic syndromes and is associated with cancer. Here, we mapped the genetic dependencies of human cell lines defective of cohesion regulators DDX11 and ESCO2. The obtained synthetic lethality networks are strongly enriched for genes involved in DNA replication and mitosis and support the existence of parallel sister chromatid cohesion establishment pathways. Among the hits, we identify the chromatin binding, BRCT-domain containing protein PAXIP1 as a novel cohesin regulator. Depletion of PAXIP1 severely aggravates cohesion defects in ESCO2 mutant cells, leading to mitotic cell death. PAXIP1 promotes global chromatin association of cohesin, independent of DNA replication, a function that cannot be explained by indirect effects of PAXIP1 on transcription or DNA repair. Cohesin regulation by PAXIP1 requires its binding partner PAGR1 and a conserved FDF motif in PAGR1. PAXIP1 co-localizes with cohesin on multiple genomic loci, including active gene promoters and enhancers. Possibly, this newly identified role of PAXIP1-PAGR1 in regulating cohesin occupancy on chromatin is also relevant for previously described functions of PAXIP1 in transcription, immune cell maturation and DNA repair.

The kleisin subunit controls the function of C. elegans meiotic cohesins by determining the mode of DNA binding and differential regulation by SCC-2 and WAPL-1.

The cohesin complex plays essential roles in chromosome segregation, 3D genome organisation, and DNA damage repair through its ability to modify DNA topology. In higher eukaryotes, meiotic chromosome function, and therefore fertility, requires cohesin complexes containing meiosis-specific kleisin subunits: REC8 and RAD21L in mammals and REC-8 and COH-3/4 in Caenorhabditis elegans. How these complexes perform the multiple functions of cohesin during meiosis and whether this involves different modes of DNA binding or dynamic association with chromosomes is poorly understood. Combining time-resolved methods of protein removal with live imaging and exploiting the temporospatial organisation of the C. elegans germline, we show that REC-8 complexes provide sister chromatid cohesion (SCC) and DNA repair, while COH-3/4 complexes control higher-order chromosome structure. High-abundance COH-3/4 complexes associate dynamically with individual chromatids in a manner dependent on cohesin loading (SCC-2) and removal (WAPL-1) factors. In contrast, low-abundance REC-8 complexes associate stably with chromosomes, tethering sister chromatids from S-phase until the meiotic divisions. Our results reveal that kleisin identity determines the function of meiotic cohesin by controlling the mode and regulation of cohesin-DNA association, and are consistent with a model in which SCC and DNA looping are performed by variant cohesin complexes that coexist on chromosomes.

A deep learning method for replicate-based analysis of chromosome conformation contacts using Siamese neural networks

The organisation of the genome in nuclear space is an important frontier of biology. Chromosome conformation capture methods such as Hi-C and Micro-C produce genome-wide chromatin contact maps that provide rich data containing quantitative and qualitative information about genome architecture. Most conventional approaches to genome-wide chromosome conformation capture data are limited to the analysis of pre-defined features, and may therefore miss important biological information. One constraint is that biologically important features can be masked by high levels of technical noise in the data. Here we introduce a replicate-based method for deep learning from chromatin conformation contact maps. Using a Siamese network configuration our approach learns to distinguish technical noise from biological variation and outperforms image similarity metrics across a range of biological systems. The features extracted from Hi-C maps after perturbation of cohesin and CTCF reflect the distinct biological functions of cohesin and CTCF in the formation of domains and boundaries, respectively. The learnt distance metrics are biologically meaningful, as they mirror the density of cohesin and CTCF binding. These properties make our method a powerful tool for the exploration of chromosome conformation capture data, such as Hi-C capture Hi-C, and Micro-C.

Preprint Highlight: Cohesin mediates DNA loop extrusion and sister chromatid cohesion by distinct mechanisms

Cohesins organize chromatin within the nucleus by promoting loop extrusion via cis contacts on chromatin and sister chromatid cohesion via trans contacts between chromatids. Whether cohesins employ a distinct mechanism for these two functions is not known. The authors use a carefully designed conditional expression of cohesin, mutated at its hinge domain, and assess its function with a variety of in vitro and in vivo experiments including live TIRF imaging, loop extrusion assay, Hi-C, and calibrated ChIP sequencing. A mutation in the hinge domain separates the two functions of cohesin, as the mutant supports loop extrusion but not sister chromatid cohesion. A unique mechanism of cohesins in promoting loop extrusion has implications for their distinct role in genome organization and for transcriptional regulation and cell fate determination. This study will be of broad interest to genome biologists with respect to these phenomena. This preprint has been assigned the following badges: New Hypothesis, New Materials. Read the preprint on bioRxiv ( Nagasaka et al., 2022 ): https://doi.org/10.1101/2022.09.23.509019 .

Cohesin-independent STAG proteins interact with RNA and R-loops and promote complex loading.

Most studies of cohesin function consider the Stromalin Antigen (STAG/SA) proteins as core complex members given their ubiquitous interaction with the cohesin ring. Here, we provide functional data to support the notion that the SA subunit is not a mere passenger in this structure, but instead plays a key role in the localization of cohesin to diverse biological processes and promotes loading of the complex at these sites. We show that in cells acutely depleted for RAD21, SA proteins remain bound to chromatin, cluster in 3D and interact with CTCF, as well as with a wide range of RNA binding proteins involved in multiple RNA processing mechanisms. Accordingly, SA proteins interact with RNA, and R-loops, even in the absence of cohesin. Our results place SA1 on chromatin upstream of the cohesin ring and reveal a role for SA1 in cohesin loading which is independent of NIPBL, the canonical cohesin loader. We propose that SA1 takes advantage of structural R-loop platforms to link cohesin loading and chromatin structure with diverse functions. Since SA proteins are pan-cancer targets, and R-loops play an increasingly prevalent role in cancer biology, our results have important implications for the mechanistic understanding of SA proteins in cancer and disease.

Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled coil arms

Structural maintenance of chromosome (SMC) complexes form ring-like structures through exceptional elongated coiled coils (CC). Recent studies found that variable CC conformations including open and collapsed forms, which might result from discontinuities in the CC, facilitate the diverse functions of SMCs in DNA organization. However, a detailed description of the SMC CC architecture is still missing. Here, we study the structural composition and mechanical properties of SMC proteins with optical tweezers unfolding experiments using the isolated Psm3 CC as a model system. We find a comparatively unstable protein with three unzipping intermediates, which we could directly assign to CC features by crosslinking experiments and state-of-the-art prediction software. Particularly, the CC elbow is shown to be a flexible, potentially non-structured feature, which divides the CC into sections, induces a pairing shift from one CC strand to the other and could facilitate large-scale conformational changes—most likely via thermal fluctuations of the flanking CC sections. A replacement of the elbow amino acids hinders folding of the consecutive CC region and leads frequently to non-native misalignments, revealing the elbow as a guide for proper folding. Additional in vivo manipulation of the elbow flexibility resulted in impaired cohesin complexes, which directly links the sensitive CC architecture to the biological function of cohesin.

Next-Generation Sequencing in the Assessment of the Transcriptomic Landscape of DNA Damage Repair Genes in Abdominal Aortic Aneurysm, Chronic Venous Disease and Lower Extremity Artery Disease.

Vascular diseases are one of the most common causes of death and morbidity. Lower extremity artery disease (LEAD), abdominal aortic aneurysm (AAA) and chronic venous disease (CVD) belong to this group of conditions and exhibit various presentations and courses; thus, there is an urgent need for revealing new biomarkers for monitoring and potential treatment. Next-generation sequencing of mRNA allows rapid and detailed transcriptome analysis, allowing us to pinpoint the most pronounced differences between the mRNA expression profiles of vascular disease patients. Comparison of expression data of 519 DNA-repair-related genes obtained from mRNA next-generation sequencing revealed significant transcriptomic marks characterizing AAA, CVD and LEAD. Statistical, gene set enrichment analysis (GSEA), gene ontology (GO) and literature analyses were applied and highlighted many DNA repair and accompanying processes, such as cohesin functions, oxidative stress, homologous recombination, ubiquitin turnover, chromatin remodelling and DNA double-strand break repair. Surprisingly, obtained data suggest the contribution of genes engaged in the regulatory function of DNA repair as a key component that could be used to distinguish between analyzed conditions. DNA repair-related genes depicted in the presented study as dysregulated in AAA, CVD and LEAD could be utilized in the design of new biomarkers or therapies associated with these diseases.

The cohesin complex of yeasts: sister chromatid cohesion and beyond.

Each time a cell divides, it needs to duplicate the genome and then separate the two copies. In eukaryotes, which usually have more than one linear chromosome, this entails tethering the two newly replicated DNA molecules, a phenomenon known as sister chromatid cohesion (SCC). Cohesion ensures proper chromosome segregation to separate poles during mitosis. SCC is achieved by the presence of the cohesin complex. Besides its canonical function, cohesin is essential for chromosome organization and DNA damage repair. Surprisingly, yeast cohesin is loaded in G1 before DNA replication starts but only acquires its binding activity during DNA replication. Work in microorganisms, such as Saccharomyces cerevisiae and Schizosaccharomyces pombe has greatly contributed to the understanding of cohesin composition and functions. In the last few years, much progress has been made in elucidating the role of cohesin in chromosome organization and compaction. Here, we discuss the different functions of cohesin to ensure faithful chromosome segregation and genome stability during the mitotic cell division in yeast. We describe what is known about its composition and how DNA replication is coupled with SCC establishment. We also discuss current models for the role of cohesin in chromatin loop extrusion and delineate unanswered questions about the activity of this important, conserved complex.

Single-molecule experiments reveal the elbow as an essential folding guide in SMC coiled-coil arms

Structural maintenance of chromosome (SMC) complexes form ring-like structures through exceptional elongated coiled-coils (CCs). Recent studies found that variable CC conformations, including open and collapsed forms, which might result from discontinuities in the CC, facilitate the diverse functions of SMCs in DNA organization. However, a detailed description of the SMC CC architecture is still missing. Here, we study the structural composition and mechanical properties of SMC proteins with optical tweezers unfolding experiments using the isolated Psm3 CC as a model system. We find a comparatively unstable protein with three unzipping intermediates, which we could directly assign to CC features by crosslinking experiments and state-of-the-art prediction software. Particularly, the CC elbow is shown to be a flexible, potentially non-structured feature, which divides the CC into sections, induces a pairing shift from one CC strand to the other and could facilitate large-scale conformational changes, most likely via thermal fluctuations of the flanking CC sections. A replacement of the elbow amino acids hinders folding of the consecutive CC region and frequently leads to non-native misalignments, revealing the elbow as a guide for proper folding. Additional in vivo manipulation of the elbow flexibility resulted in impaired cohesin complexes, which directly link the sensitive CC architecture to the biological function of cohesin.

Depletion or cleavage of cohesin during anaphase differentially affects chromatin structure and segregation.

Chromosome segregation requires both the separation of sister chromatids and the sustained condensation of chromatids during anaphase. In yeast cells, cohesin is not only required for sister chromatid cohesion but also plays a major role determining the structure of individual chromatids in metaphase. Separase cleavage is thought to remove all cohesin complexes from chromosomes to initiate anaphase. It is thus not clear how the length and organisation of segregating chromatids is maintained during anaphase in the absence of cohesin. Here, we show that degradation of cohesin at the anaphase onset causes aberrant chromatid segregation. Hi-C analysis on segregating chromatids demonstrates that cohesin depletion causes loss of intrachromatid organisation. Surprisingly, tobacco etch virus (TEV)-mediated cleavage of cohesin does not dramatically disrupt chromatid organisation in anaphase, explaining why bulk segregation is achieved. In addition, we identified a small pool of cohesin complexes bound to telophase chromosomes in wild-type cells and show that they play a role in the organisation of centromeric regions. Our data demonstrates that in yeast cells cohesin function is not over in metaphase, but extends to the anaphase period when chromatids are segregating.

CohesinDB: a comprehensive database for decoding cohesin-related epigenomes, 3D genomes and transcriptomes in human cells.

Cohesin is a multifunctional protein responsible for transcriptional regulation and chromatin organization. Cohesin binds to chromatin at tens of thousands of distinct sites in a conserved or tissue-specific manner, whereas the function of cohesin varies greatly depending on the epigenetic properties of specific chromatin loci. Cohesin also extensively mediates cis-regulatory modules (CRMs) and chromatin loops. Even though next-generation sequencing technologies have provided a wealth of information on different aspects of cohesin, the integration and exploration of the resultant massive cohesin datasets are not straightforward. Here, we present CohesinDB (https://cohesindb.iqb.u-tokyo.ac.jp), a comprehensive multiomics cohesin database in human cells. CohesinDB includes 2043 epigenomics, transcriptomics and 3D genomics datasets from 530 studies involving 176 cell types. By integrating these large-scale data, CohesinDB summarizes three types of 'cohesin objects': 751 590 cohesin binding sites, 957 868 cohesin-related chromatin loops and 2229 500 cohesin-related CRMs. Each cohesin object is annotated with locus, cell type, classification, function, 3D genomics and cis-regulatory information. CohesinDB features a user-friendly interface for browsing, searching, analyzing, visualizing and downloading the desired information. CohesinDB contributes a valuable resource for all researchers studying cohesin, epigenomics, transcriptional regulation and chromatin organization.

PDS5A and PDS5B differentially affect gene expression without altering cohesin localization across the genome

BackgroundCohesin is an important structural regulator of the genome, regulating both three-dimensional genome organization and gene expression. The core cohesin trimer interacts with various HEAT repeat accessory subunits, yielding cohesin complexes of distinct compositions and potentially distinct functions. The roles of the two mutually exclusive HEAT repeat subunits PDS5A and PDS5B are not well understood.ResultsHere, we determine that PDS5A and PDS5B have highly similar localization patterns across the mouse embryonic stem cell (mESC) genome and they show a strong overlap with other cohesin HEAT repeat accessory subunits, STAG1 and STAG2. Using CRISPR/Cas9 genome editing to generate individual stable knockout lines for PDS5A and PDS5B, we find that loss of one PDS5 subunit does not alter the distribution of the other PDS5 subunit, nor the core cohesin complex. Both PDS5A and PDS5B are required for proper gene expression, yet they display only partially overlapping effects on gene targets. Remarkably, gene expression following dual depletion of the PDS5 HEAT repeat proteins does not completely overlap the gene expression changes caused by dual depletion of the STAG HEAT repeat proteins, despite the overlapping genomic distribution of all four proteins. Furthermore, dual loss of PDS5A and PDS5B decreases cohesin association with NIPBL and WAPL, reduces SMC3 acetylation, and does not alter overall levels of cohesin on the genome.ConclusionsThis work reveals the importance of PDS5A and PDS5B for proper cohesin function. Loss of either subunit has little effect on cohesin localization across the genome yet PDS5A and PDS5B are differentially required for gene expression.

STAG2 promotes the myelination transcriptional program in oligodendrocytes.

Cohesin folds chromosomes via DNA loop extrusion. Cohesin-mediated chromosome loops regulate transcription by shaping long-range enhancer-promoter interactions, among other mechanisms. Mutations of cohesin subunits and regulators cause human developmental diseases termed cohesinopathy. Vertebrate cohesin consists of SMC1, SMC3, RAD21, and either STAG1 or STAG2. To probe the physiological functions of cohesin, we created conditional knockout (cKO) mice with Stag2 deleted in the nervous system. Stag2 cKO mice exhibit growth retardation, neurological defects, and premature death, in part due to insufficient myelination of nerve fibers. Stag2 cKO oligodendrocytes exhibit delayed maturation and downregulation of myelination-related genes. Stag2 loss reduces promoter-anchored loops at downregulated genes in oligodendrocytes. Thus, STAG2-cohesin generates promoter-anchored loops at myelination-promoting genes to facilitate their transcription. Our study implicates defective myelination as a contributing factor to cohesinopathy and establishes oligodendrocytes as a relevant cell type to explore the mechanisms by which cohesin regulates transcription.

Postmitotic differentiation of human monocytes requires cohesin-structured chromatin

Cohesin is a major structural component of mammalian genomes and is required to maintain loop structures. While acute depletion in short-term culture models suggests a limited importance of cohesin for steady-state transcriptional circuits, long-term studies are hampered by essential functions of cohesin during replication. Here, we study genome architecture in a postmitotic differentiation setting, the differentiation of human blood monocytes (MO). We profile and compare epigenetic, transcriptome and 3D conformation landscapes during MO differentiation (either into dendritic cells or macrophages) across the genome and detect numerous architectural changes, ranging from higher level compartments down to chromatin loops. Changes in loop structures correlate with cohesin-binding, as well as epigenetic and transcriptional changes during differentiation. Functional studies show that the siRNA-mediated depletion of cohesin (and to a lesser extent also CTCF) markedly disturbs loop structures and dysregulates genes and enhancers that are primarily regulated during normal MO differentiation. In addition, gene activation programs in cohesin-depleted MO-derived macrophages are disturbed. Our findings implicate an essential function of cohesin in controlling long-term, differentiation- and activation-associated gene expression programs.