Long-range Enhancer-promoter Interactions Research Articles

SnapHiC-G: identifying long-range enhancer-promoter interactions from single-cell Hi-C data via a global background model.

Harnessing the power of single-cell genomics technologies, single-cell Hi-C (scHi-C) and its derived technologies provide powerful tools to measure spatial proximity between regulatory elements and their target genes in individual cells. Using a global background model, we propose SnapHiC-G, a computational method, to identify long-range enhancer-promoter interactions from scHi-C data. We applied SnapHiC-G to scHi-C datasets generated from mouse embryonic stem cells and human brain cortical cells. SnapHiC-G achieved high sensitivity in identifying long-range enhancer-promoter interactions. Moreover, SnapHiC-G can identify putative target genes for noncoding genome-wide association study (GWAS) variants, and the genetic heritability of neuropsychiatric diseases is enriched for single-nucleotide polymorphisms (SNPs) within SnapHiC-G-identified interactions in a cell-type-specific manner. In sum, SnapHiC-G is a powerful tool for characterizing cell-type-specific enhancer-promoter interactions from complex tissues and can facilitate the discovery of chromatin interactions important for gene regulation in biologically relevant cell types.

Conserved Cis-Acting Range Extender Element Mediates Extreme Long-Range Enhancer Activity in Mammals.

While most mammalian enhancers regulate their cognate promoters over moderate distances of tens of kilobases (kb), some enhancers act over distances in the megabase range. The sequence features enabling such extreme-distance enhancer-promoter interactions remain elusive. Here, we used in vivo enhancer replacement experiments in mice to show that short- and medium-range enhancers cannot initiate gene expression at extreme-distance range. We uncover a novel conserved cis-acting element, Range EXtender (REX), that confers extreme-distance regulatory activity and is located next to a long-range enhancer of Sall1. The REX element itself has no endogenous enhancer activity. However, addition of the REX to other short- and mid-range enhancers substantially increases their genomic interaction range. In the most extreme example observed, addition of the REX increased the range of an enhancer by an order of magnitude, from its native 71kb to 840kb. The REX element contains highly conserved [C/T]AATTA homeodomain motifs. These motifs are enriched around long-range limb enhancers genome-wide, including the ZRS, a benchmark long-range limb enhancer of Shh. Mutating the [C/T]AATTA motifs within the ZRS does not affect its limb-specific enhancer activity at short range, but selectively abolishes its long-range activity, resulting in severe limb reduction in knock-in mice. In summary, we identify a sequence signature globally associated with long-range enhancer-promoter interactions and describe a prototypical REX element that is necessary and sufficient to confer extreme-distance gene activation by remote enhancers.

4D nucleome equation predicts gene expression controlled by long-range enhancer-promoter interaction.

Recent experimental evidence strongly supports that three-dimensional (3D) long-range enhancer-promoter (E-P) interactions have important influences on gene-expression dynamics, but it is unclear how the interaction information is translated into gene expression over time (4D). To address this question, we developed a general theoretical framework (named as a 4D nucleome equation), which integrates E-P interactions on chromatin and biochemical reactions of gene transcription. With this equation, we first present the distribution of mRNA counts as a function of the E-P genomic distance and then reveal a power-law scaling of the expression level in this distance. Interestingly, we find that long-range E-P interactions can induce bimodal and trimodal mRNA distributions. The 4D nucleome equation also allows for model selection and parameter inference. When this equation is applied to the mouse embryonic stem cell smRNA-FISH data and the E-P genomic-distance data, the predicted E-P contact probability and mRNA distribution are in good agreement with experimental results. Further statistical inference indicates that the E-P interactions prefer to modulate the mRNA level by controlling promoter activation and transcription initiation rates. Our model and results provide quantitative insights into both spatiotemporal gene-expression determinants (i.e., long-range E-P interactions) and cellular fates during development.

The Transcriptional Landscape of Ph+B-ALL Is Orchestrated By Long-Range Enhancer-Promoter Interactions and the Coordinated Action of Phosphorylation-Dependent and Phosphorylation-Independent Transcription Factors

Background and Hypothesis: B-cell precursor leukaemia (B-ALL) subtypes can be distinguished by their initiating genetic lesions. Likewise, each subtype exhibits a unique transcriptional program that drives the malignancy and defines the subtype. This often relates to the initiating genetic alteration that affects genes encoding transcription factors (TFs). However, for B-ALLs not driven by TF alterations it is less clear how the transcriptional program is established. Ph+B-ALL is a historically poor prognosis B-ALL driven by the BCR::ABL1 oncogene, a constitutive tyrosine kinase that activates its targets via phosphorylation. We hypothesised that BCR::ABL1 initiates the transcriptional signature of Ph+B-ALL cells by a two-step mechanism involving phosphorylation-activatable TFs, which then induce the expression of additional TFs that consecutively establish the Ph+B-ALL-defining transcriptome. As gene expression is often modulated by cis-regulatory elements such as enhancers, we further speculated that BCR::ABL1 reprograms the enhancer landscape to promote the transcriptional changes that define Ph+B-ALL. Results: Using an in vitro model of BCR::ABL1-induced transformation of murine B-cell precursors, we show that transcriptional deregulation by BCR::ABL1 is a continuous process evolving until full transformation is established. Only a minority of induced transcriptional changes occur immediately upon BCR::ABL1 expression (3 days), while most affected genes require an extended period of BCR::ABL1 to become deregulated. Furthermore, less than half of deregulated genes in murine Ph+B-ALL and less than 10% of human Ph+B-ALL-defining genes were sensitive to 24h BCR::ABL1 inhibition, suggesting an involvement of phosphorylation-dependent and phosphorylation-independent TFs. TF motif enrichment analysis of active chromatin in human and mouse Ph+B-ALL cells indicated the phosphorylation-dependent TF STAT5 and the phosphorylation-independent TF ETV5 as main mediators. Degron-induced rapid degradation of each TF in Ph+B-ALL cells confirmed their unique and overlapping roles and coordinated action. In parallel to gene expression changes, Ph+B-ALL cells further acquire changes in their enhancer signatures defined by H3K27ac+ at non-promoter regions, and these enhancer signatures can be efficiently used to distinguish Ph+B-ALL from other B-ALL subtypes. Analysis of chromatin interactions of these active enhancers with respective active promoters by Promoter-Capture Hi-C (PCHI-C) in combination with H3K27ac-ChIP-Seq showed that most active genes in Ph+B-ALL cells physically interact with an enhancer, including many genes described to be essential for Ph+B-ALL cells, such as CCND2, BCL2, BCL2L1, and ETV5. Using PCHI-C and H3K27ac-HiChIP we further show that, like gene expression and enhancer signatures, physical contacts of promoters and enhancers can be efficiently used to identify Ph+B-ALL cells and distinguish them from other B-ALLs such as KMT2A-rearranged B-ALL. Subtype-specific chromatin interactions that allow this differentiation directly relate to the transcriptional programs that define the respective B-ALL subtype. Conclusion: We describe here the molecular details of how signals from an oncogenic tyrosine kinase become converted into changes in gene expression that define the B-lineage leukaemia subtype Ph+B-ALL. Our work highlights the complexity of these changes by acknowledging the role of gene regulatory elements/enhancers in this process and further describe for the first time that B-ALL subtypes can be distinguished by their enhancer usage and promoter-enhancer interactions. Uncovering the precise enhancer regions for the genes deregulated in Ph+B-ALL and the TFs recruited to them may open new windows for therapeutic intervention.

Prioritization of risk genes in colorectal cancer by integrative analysis of multi-omics data and gene networks.

Genome-wide association studies (GWASs) have identified over 140 colorectal cancer (CRC)-associated loci; however, target genes at the majority of loci and underlying molecular mechanisms are poorly understood. Here, we utilized a Bayesian approach, integrative risk gene selector (iRIGS), to prioritize risk genes at CRC GWAS loci by integrating multi-omics data. As a result, a total of 105 high-confidence risk genes (HRGs) were identified, which exhibited strong gene dependencies for CRC and enrichment in the biological processes implicated in CRC. Among the 105 HRGs, CEBPB, located at the 20q13.13 locus, acted as a transcription factor playing critical roles in cancer. Our subsequent assays indicated the tumor promoter function of CEBPB that facilitated CRC cell proliferation by regulating multiple oncogenic pathways such as MAPK, PI3K-Akt, and Ras signaling. Next, by integrating a fine-mapping analysis and three independent case-control studies in Chinese populations consisting of 8,039 cases and 12,775 controls, we elucidated that rs1810503, a putative functional variant regulating CEBPB, was associated with CRC risk (OR=0.90, 95%CI=0.86-0.93, P=1.07×10-7). The association between rs1810503 and CRC risk was further validated in three additional multi-ancestry populations consisting of 24,254 cases and 58,741 controls. Mechanistically, the rs1810503 A to T allele change weakened the enhancer activity in an allele-specific manner to decrease CEBPB expression via long-range promoter-enhancer interactions, mediated by the transcription factor, REST, and thus decreased CRC risk. In summary, our study provides a genetic resource and a generalizable strategy for CRC etiology investigation, and highlights the biological implications of CEBPB in CRC tumorigenesis, shedding new light on the etiology of CRC.

The chromatin- triple helix connection.

Mammalian genomes are extensively transcribed, producing a large number of coding and non-coding transcripts. A large fraction of the nuclear RNAs is physically associated with chromatin, functioning in gene activation and silencing, shaping higher-order genome organisation, such as involvement in long-range enhancer-promoter interactions, transcription hubs, heterochromatin, nuclear bodies and phase transitions. Different mechanisms allow the tethering of these chromatin-associated RNAs (caRNA) to chromosomes, including RNA binding proteins, the RNA polymerases and R-loops. In this review, we focus on the sequence-specific targeting of RNA to DNA by forming triple helical structures and describe its interplay with chromatin. It turns out that nucleosome positioning at triple helix target sites and the nucleosome itself are essential factors in determining the formation and stability of triple helices. The histone H3-tail plays a critical role in triple helix stabilisation, and the role of its epigenetic modifications in this process is discussed.

Remote regulation of rs80245547 and rs72673891 mediated by transcription factors C-Jun and CREB1 affect GSTCD expression

Chronic obstructive pulmonary disease (COPD), the third leading cause of death worldwide, is influenced by genetic factors. The genetic signal rs10516526 in the glutathione S-transferase C-terminal domain containing (GSTCD) gene is a highly significant and reproducible signal associated with lung function and COPD on chromosome 4q24. In this study, comprehensive bioinformatics analyses and experimental verifications were detailly implemented to explore the regulation mechanism of rs10516526 and GSTCD in COPD. The results suggested that low expression of GSTCD was associated with COPD (p= 0.010). And C-Jun and CREB1 transcription factors were found to be essential for the regulation of GSTCD by rs80245547 and rs72673891. Moreover, rs80245547T and rs72673891G had a stronger binding ability to these transcription factors, which may promote the allele-specific long-range enhancer-promoter interactions on GSTCD, thus making COPD less susceptible. Our study provides a new insight into the relationship between rs10516526, GSTCD, and COPD.

Vorinostat-induced acetylation of RUNX3 reshapes transcriptional profile through long-range enhancer-promoter interactions in natural killer cells

Natural killer (NK) cells are an essential part of the innate immune system that helps control infections and tumors. Recent studies have shown that Vorinostat, a histone deacetylase (HDAC) inhibitor, can cause significant changes in gene expression and signaling pathways in NK cells. Since gene expression in eukaryotic cells is closely linked to the complex three-dimensional (3D) chromatin architecture, an integrative analysis of the transcriptome, histone profiling, chromatin accessibility, and 3D genome organization is needed to gain a more comprehensive understanding of how Vorinostat impacts transcription regulation of NK cells from a chromatin-based perspective. The results demonstrate that Vorinostat treatment reprograms the enhancer landscapes of the human NK-92 NK cell line while overall 3D genome organization remains largely stable. Moreover, we identified that the Vorinostat-induced RUNX3 acetylation is linked to the increased enhancer activity, leading to elevated expression of immune response-related genes via long-range enhancerpromoter chromatin interactions. In summary, these findings have important implications in the development of new therapies for cancer and immune-related diseases by shedding light on the mechanisms underlying Vorinostat's impact on transcriptional regulation in NK cells within the context of 3D enhancer network.

Nuclear condensates of YAP fusion proteins alter transcription to drive ependymoma tumourigenesis.

Nuclear localization of HIPPO-YAP fusion proteins has been implicated in supratentorial ependymoma development. Here, unexpectedly, we find that liquid-liquid phase separation, rather than nuclear localization, of recurrent patient-derived YAP fusions, YAP-MAMLD1 and C11ORF95-YAP, underlies ependymoma tumourigenesis from neural progenitor cells. Mutagenesis and chimaera assays demonstrate that an intrinsically disordered region promotes oligomerization of the YAP fusions into nuclear, puncta-like, membrane-less condensates. Oligomerization and nuclear condensates induced by YAP fusion with a coiled-coil domain of transcriptional activator GCN4 also promote ependymoma formation. YAP-MAMLD1 concentrates transcription factors and co-activators, including BRD4, MED1 and TEAD, in condensates while excluding transcriptional repressive PRC2, and induces long-range enhancer-promoter interactions that promote transcription and oncogenic programmes. Blocking condensate-mediated transcriptional co-activator activity inhibits tumourigenesis, indicating a critical role of liquid phase separation for YAP fusion oncogenic activity in ependymoma. YAP fusions containing the intrinsically disordered region features are common in human tumours, suggesting that nuclear condensates could be targeted to treat YAP-fusion-induced cancers.

Genome organization controls transcriptional dynamics during development.

Past studies offer contradictory claims for the role of genome organization in the regulation of gene activity. Here, we show through high-resolution chromosome conformation analysis that the Drosophila genome is organized by two independent classes of regulatory sequences, tethering elements and insulators. Quantitative live imaging and targeted genome editing demonstrate that this two-tiered organization is critical for the precise temporal dynamics of Hox gene transcription during development. Tethering elements mediate long-range enhancer-promoter interactions and foster fast activation kinetics. Conversely, the boundaries of topologically associating domains (TADs) prevent spurious interactions with enhancers and silencers located in neighboring TADs. These two levels of genome organization operate independently of one another to ensure precision of transcriptional dynamics and the reliability of complex patterning processes.

Mechanism of REST/NRSF regulation of clustered protocadherin α genes.

Repressor element-1 silencing transcription factor (REST) or neuron-restrictive silencer factor (NRSF) is a zinc-finger (ZF) containing transcriptional repressor that recognizes thousands of neuron-restrictive silencer elements (NRSEs) in mammalian genomes. How REST/NRSF regulates gene expression remains incompletely understood. Here, we investigate the binding pattern and regulation mechanism of REST/NRSF in the clustered protocadherin (PCDH) genes. We find that REST/NRSF directionally forms base-specific interactions with NRSEs via tandem ZFs in an anti-parallel manner but with striking conformational changes. In addition, REST/NRSF recruitment to the HS5–1 enhancer leads to the decrease of long-range enhancer-promoter interactions and downregulation of the clustered PCDHα genes. Thus, REST/NRSF represses PCDHα gene expression through directional binding to a repertoire of NRSEs within the distal enhancer and variable target genes.

3D reconstruction of genomic regions from sparse interaction data.

Chromosome conformation capture (3C) technologies measure the interaction frequency between pairs of chromatin regions within the nucleus in a cell or a population of cells. Some of these 3C technologies retrieve interactions involving non-contiguous sets of loci, resulting in sparse interaction matrices. One of such 3C technologies is Promoter Capture Hi-C (pcHi-C) that is tailored to probe only interactions involving gene promoters. As such, pcHi-C provides sparse interaction matrices that are suitable to characterize short- and long-range enhancer–promoter interactions. Here, we introduce a new method to reconstruct the chromatin structural (3D) organization from sparse 3C-based datasets such as pcHi-C. Our method allows for data normalization, detection of significant interactions and reconstruction of the full 3D organization of the genomic region despite of the data sparseness. Specifically, it builds, with as low as the 2–3% of the data from the matrix, reliable 3D models of similar accuracy of those based on dense interaction matrices. Furthermore, the method is sensitive enough to detect cell-type-specific 3D organizational features such as the formation of different networks of active gene communities.

EPEN-04. ONCOGENIC 3D TUMOR GENOME ORGANIZATION IDENTIFIES NEW THERAPEUTIC TARGETS IN EPENDYMOMA

By profiling enhancers in primary ependymoma tumors, we have recently identified putative oncogenes, molecular targets, and functional pathways. Inhibition of selected targets diminished the proliferation of patient-derived neurospheres and increased survival in mouse models of ependymoma. While enhancers frequently regulate the nearest gene, identification of enhancer target genes remains to be a challenge in the absence of chromosome conformation information. Consequently, we have now used HiC to map the 3-dimensional organization of tumor chromatin in the two most common and aggressive ependymoma subgroups: posterior fossa group A (PF-EPN-A) and supratentorial ependymomas with gene fusions involving the NF-κB subunit gene RELA (ST-EPN-RELA). By an integrative analysis of enhancer and gene expression in the context of the newly derived HiC data, we find that a large number of the predicted enhancer target genes are enriched for strong physical interactions. Importantly, we also identify many new putative tumor-dependency genes activated by long-range promoter-enhancer interactions and complex tumor-specific chromatin clusters of regulatory elements. Complementary to the analysis of gene-enhancer interactions, we have also leveraged the HiC data for resolving structural rearrangements underlying copy number alterations. Copy number gains of the 1q arm of chromosome 1 are especially associated with poor survival. Our preliminary results in PFA relapse samples show complex structural variants underlying 1q gain that lead to inter-chromosomal rearrangements and affect several genes that potentially contribute to poor survival. In ongoing work we are testing the relevance of the novel candidate genes for tumor cell growth and proliferation in-patient derived ependymoma models.

Crystal structure of human LDB1 in complex with SSBP2

The Lim domain binding proteins (LDB1 and LDB2 in human and Chip in Drosophila) play critical roles in cell fate decisions through partnership with multiple Lim-homeobox and Lim-only proteins in diverse developmental systems including cardiogenesis, neurogenesis, and hematopoiesis. In mammalian erythroid cells, LDB1 dimerization supports long-range connections between enhancers and genes involved in erythropoiesis, including the β-globin genes. Single-stranded DNA binding proteins (SSBPs) interact specifically with the LDB/Chip conserved domain (LCCD) of LDB proteins and stabilize LDBs by preventing their proteasomal degradation, thus promoting their functions in gene regulation. The structural basis for LDB1 self-interaction and interface with SSBPs is unclear. Here we report a crystal structure of the human LDB1/SSBP2 complex at 2.8-Å resolution. The LDB1 dimerization domain (DD) contains an N-terminal nuclear transport factor 2 (NTF2)-like subdomain and a small helix 4-helix 5 subdomain, which together form the LDB1 dimerization interface. The 2 LCCDs in the symmetric LDB1 dimer flank the core DDs, with each LCCD forming extensive interactions with an SSBP2 dimer. The conserved linker between LDB1 DD and LCCD covers a potential ligand-binding pocket of the LDB1 NTF2-like subdomain and may serve as a regulatory site for LDB1 structure and function. Our structural and biochemical data provide a much-anticipated structural basis for understanding how LDB1 and the LDB1/SSBP interactions form the structural core of diverse complexes mediating cell choice decisions and long-range enhancer-promoter interactions.

GENE-15. TARGETING OF EPENDYMOMA AS INFORMED BY ONCOGENIC 3D GENOME ORGANIZATION

Abstract By profiling enhancers in primary ependymoma tumors, we have recently identified putative oncogenes, molecular targets, and functional pathways. Inhibition of selected targets diminished the proliferation of patient-derived neurospheres and increased survival in mouse models of ependymoma. While enhancers frequently regulate the nearest gene, unambiguous identification of enhancer target genes remains to be a challenge in the absence of chromosome conformation information. Consequently, we have now used HiC to map the 3-dimensional organization of tumor chromatin in the two most common and aggressive ependymoma subgroups: posterior fossa group A (PF-EPN-A) and supratentorial ependymomas with gene fusions involving the NF-κB subunit gene RELA (ST-EPN-RELA). By an integrative analysis of enhancer and gene expression in the context of the newly derived HiC data, we find that a large amount of the previously predicted enhancer target genes can be confirmed by physical interactions. Importantly, we also identify many new putative tumor-dependency genes activated by long-range promoter-enhancer interactions. Complementary to the analysis of gene-enhancer interactions, we have also leveraged the HiC data for resolving structural rearrangements underlying copy number alterations frequently observed in PF-EPN-A tumors. Especially copy number gains of the 1q arm of chromosome 1 are associated with poor survival. Our preliminary results reveal complex structural variants that underlie 1q gains, which lead to inter-chromosomal rearrangements and affect several genes that potentially contribute to poor survival. We now aim to test the relevance of the novel candidate tumor-dependency genes for tumor cell growth and proliferation in patient derived ependymoma models.

Integrating distal and proximal information to predict gene expression via a densely connected convolutional neural network.

Interactions among cis-regulatory elements such as enhancers and promoters are main driving forces shaping context-specific chromatin structure and gene expression. Although there have been computational methods for predicting gene expression from genomic and epigenomic information, most of them neglect long-range enhancer-promoter interactions, due to the difficulty in precisely linking regulatory enhancers to target genes. Recently, HiChIP, a novel high-throughput experimental approach, has generated comprehensive data on high-resolution interactions between promoters and distal enhancers. Moreover, plenty of studies suggest that deep learning achieves state-of-the-art performance in epigenomic signal prediction, and thus promoting the understanding of regulatory elements. In consideration of these two factors, we integrate proximal promoter sequences and HiChIP distal enhancer-promoter interactions to accurately predict gene expression. We propose DeepExpression, a densely connected convolutional neural network, to predict gene expression using both promoter sequences and enhancer-promoter interactions. We demonstrate that our model consistently outperforms baseline methods, not only in the classification of binary gene expression status but also in regression of continuous gene expression levels, in both cross-validation experiments and cross-cell line predictions. We show that the sequential promoter information is more informative than the experimental enhancer information; meanwhile, the enhancer-promoter interactions within ±100 kbp around the TSS of a gene are most beneficial. We finally visualize motifs in both promoter and enhancer regions and show the match of identified sequence signatures with known motifs. We expect to see a wide spectrum of applications using HiChIP data in deciphering the mechanism of gene regulation. DeepExpression is freely available at https://github.com/wanwenzeng/DeepExpression. Supplementary data are available at Bioinformatics online.

Chromatin-associated RNAs as facilitators of functional genomic interactions.

Mammalian genomes are extensively transcribed, which produces a large number of both coding and non-coding transcripts. Various RNAs are physically associated with chromatin, through being either retained in cis at their site of transcription or recruited in trans to other genomic regions. Driven by recent technological innovations for detecting chromatin-associated RNAs, diverse roles are being revealed for these RNAs and associated RNA-binding proteins (RBPs) in gene regulation and genome function. Such functions include locus-specific roles in gene activation and silencing, as well as emerging roles in higher-order genome organization, such as involvement in long-range enhancer-promoter interactions, transcription hubs, heterochromatin, nuclear bodies and phase transitions.

Modeling the relationship of diverse genomic signatures to gene expression levels with the regulation of long-range enhancer-promoter interactions

Enhancer–promoter (E–P) interaction is an essential component of cis-regulatory regulation for gene expression. However, to comprehensively study the gene expression with the regulation of long-range E–P interactions is a major challenge in the regulatory networks. As these types of gene expression are regulated by diverse genomic signatures, we presented a computational method to study the relationships between gene expression levels and diverse genomic signatures. In this paper, based on the datasets of long-range E–P interactions, we extracted feature parameters from multiple signatures (e.g., epigenetic marks, transcription factors) and used regression models to predict the gene expression levels. In our results, we found that the predicted expression values correlated well with the measured expression values in both the interacting and non-interacting sets, and the correlation values of the interacting set were higher than that of the corresponding non-interacting set in each cell line, which indicated that the distal enhancers would cooperate with diverse genomic signatures to facilitate the expression level of target genes. By comparing the important signature features for the gene expression levels between the interacting and non-interacting sets in the same cell line, we found that the important specific signatures affect the gene expression regulated by distal enhancers. Our research provided additional insights about the roles of diverse signatures in gene expression with the regulation of distal enhancers.

Recognition of long-range enhancer-promoter interactions by adding genomic signatures of segmented regulatory regions

Enhancer-promoter interaction (EPI) is an important cis-regulatory mechanism in the regulation of tissue-specific gene expression. However, it still has limitation to precisely identity these interactions so far. In this paper, using diverse genomic features for various regulatory regions, we presented a computational approach to predict EPIs with improved accuracies. Meanwhile, we comprehensively studied more potential regulatory factors that are important to EPIs prediction, such as nucleosome occupancy, enhancer RNA; and found the cell line-specificity and region-specificity of the contributions of diverse regulatory signatures. By adding genomic signatures of segmented regulatory regions, our best accuracies of cross-validation test were about 11%–16% higher than the previous results, indicating the location-specificity of genomic signatures in a regulatory region for predicting EPIs. Additionally, more training samples and related features can provide reliable performances in new cell lines. Consequently, our study provided additional insights into the roles of diverse signature features for predicting long-range EPIs.

Zebrafish as a Model to Study Cohesin and Cohesinopathies.

The cohesin protein complex regulates multiple cellular events including sister chromatid cohesion and gene expression. Several distinct human diseases called cohesinopathies have been associated with genetic mutations in cohesin subunit genes or genes encoding regulators of cohesin function. Studies in different model systems, from yeast to mouse have provided insights into the molecular mechanisms of action of cohesin/cohesin regulators and their implications in the pathogenesis of cohesinopathies. The zebrafish has unique advantages for embryonic analyses and quantitative gene knockdown with morpholinos during the first few days of development, in contrast to knockouts of cohesin regulators in flies or mammals, which are either lethal as homozygotes or dramatically compensated for in heterozygotes. This has been particularly informative for Rad21, where a role in gene expression was first shown in zebrafish, and Nipbl, where the fish work revealed tissue-specific functions in heart, gut, and limbs, and long-range enhancer-promoter interactions that control Hox gene expression in vivo. Here we discuss the utility of the zebrafish in studying the developmental and pathogenic roles of cohesin.