Galaxy HiCExplorer: a web server for reproducible Hi-C data analysis, quality control and visualization

Identification of ZNF384 as a regulator of epigenome in leukemia

Leukemia is a complex hematologic cancer driven by genetic and epigenetic changes that impact gene expression. Understanding these molecular mechanisms is essential for improving leukemia diagnosis and prognosis. This study examines the role of the zinc finger protein ZNF384 in the epigenome and its influence on gene regulation in leukemia. We analyzed next-generation sequencing data from The Encyclopedia of DNA Elements (ENCODE), integrating datasets such as chromatin immunoprecipitation sequencing (ChIP-seq) of ZNF384 and regulatory histone marks, RNA sequencing (RNA-seq), and Hi-C data from K562 and GM12878 cells. Additionally, we used RNA-seq from K562 ZNF384 knock-down (KD) cells generated via CRISPR interference (CRISPRi) to validate our findings. This enabled us to explore the chromatin interaction patterns of ZNF384 and its regulatory impact. Our results demonstrate that ZNF384 associates with promoters and enhancers in K562 and GM12878 cells, facilitating increased transcription levels. We also found ZNF384 enriched at topologically associating domain (TAD) boundaries and chromatin loops, suggesting a role in three-dimensional (3D) chromatin organization. Furthermore, we identified a significant binding of ZNF384 at SINE-Alu elements in both K562 and GM12878 cells. In summary, this study highlights the regulatory role of ZNF384 in the leukemia epigenome and its impact on gene expression. Understanding the oncogenic implications of ZNF384 may improve leukemia diagnosis and prognosis.

Endometrial tumorigenesis involves epigenetic plasticity demarcating non-coding somatic mutations and 3D-genome alterations

BACKGROUND

The incidence and mortality of endometrial cancer (EC) is on the rise. Eighty-five percent of ECs depend on estrogen receptor alpha (ERα) for proliferation, but little is known about its transcriptional regulation in these tumors.

RESULTS

We generate epigenomics, transcriptomics, and Hi-C datastreams in healthy and tumor endometrial tissues, identifying robust ERα reprogramming and profound alterations in 3D genome organization that lead to a gain of tumor-specific enhancer activity during EC development. Integration with endometrial cancer risk single-nucleotide polymorphisms and whole-genome sequencing data from primary tumors and metastatic samples reveals a striking enrichment of risk variants and non-coding somatic mutations at tumor-enriched ERα sites. Through machine learning-based predictions and interaction proteomics analyses, we identify an enhancer mutation which alters 3D genome conformation, impairing recruitment of the transcriptional repressor EHMT2/G9a/KMT1C, thereby alleviating transcriptional repression of ESR1 in EC.

CONCLUSIONS

In summary, we identify a complex genomic-epigenomic interplay in EC development and progression, altering 3D genome organization to enhance expression of the critical driver ERα.

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

In mammals, cohesin and CTCF organize the 3D genome into topologically associating 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 have also been 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-1 depletion supports the idea that cohesin is preferentially loaded at sites bound by the C. elegans ortholog of NIPBL 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 owing 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 with mammals, the average processivity of C. elegans cohesin is about 10-fold shorter, and the binding of NIPBL ortholog 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.

Detection of Gene Fusions and Rearrangements in Formalin-Fixed, Paraffin-Embedded Solid Tumor Specimens Using High-Throughput Chromosome Conformation Capture

Chromosomal structural variants (SVs) are major contributors to cancer development. Although multiple methods exist for detecting SVs, they are limited in throughput, such as fluorescent in situ hybridization and targeted panels, and use RNA, which degrades in formalin-fixed, paraffin-embedded (FFPE) blocks and is unable to detect SVs that do not produce a fusion transcript. High-throughput chromosome conformation capture (Hi-C) is a DNA-based next-generation sequencing (NGS) method that preserves the spatial conformation of the genome, capturing long-range genetic interactions and SVs. Herein, a retrospective study analyzing 71 FFPE specimens from 10 different solid tumors was performed. Results showed high concordance (98%) with clinical fluorescent in situ hybridization and RNA NGS in detecting known SVs. Furthermore, Hi-C provided insight into the mechanism of SV formation, including chromothripsis and extrachromosomal DNA, and detected rearrangements between genes and regulatory regions, all of which are undetectable by RNA NGS. Lastly, SVs were detected in 71% of cases in which previous clinical methods failed to identify a driver. Of these, 14% were clinically actionable based on current medical guidelines, and an additional 14% were not in medical guidelines but involve targetable biomarkers. Current data suggest that Hi-C is a robust and accurate method for genome-wide SV analyses from FFPE tissue and can be incorporated into current clinical NGS workflows.

Genomic and Methylomic Signatures Associated With the Maintenance of Genome Stability and Adaptive Evolution in Two Closely Allied Wolf Spiders

Pardosa spiders, belonging to the wolf spider family Lycosidae, play a vital role in maintaining the health of forest and agricultural ecosystems due to their function in pest control. This study presents chromosome-level genome assemblies for two allied Pardosa species, P. laura and P. agraria. Both species' genomes show a notable expansion of helitron transposable elements, which contributes to their large genome sizes. Methylome analysis indicates that P. laura has higher overall DNA methylation levels compared to P. agraria. DNA methylation may not only aids in transposable element-driven genome expansion but also positively affects the three-dimensional organisation of P. laura after transposon amplification, thereby potentially enhancing genome stability. Genes associated with hyper-differentially methylated regions in P. laura (compared to P. agraria) are enriched in functions related to mRNA processing and energy production. Furthermore, combined transcriptome and methylome profiling has uncovered a complex regulatory interplay between DNA methylation and gene expression, emphasising the important role of gene body methylation in the regulation of gene expression. Comparative genomic analysis shows a significant expansion of cuticle protein and detoxification-related gene families in P. laura, which may improve its adaptability to various habitats. This study provides essential genomic and methylomic insights, offering a deeper understanding of the relationship between transposable elements and genome stability, and illuminating the adaptive evolution and species differentiation among allied spiders.

DNA methyltransferase 1 modulates mitochondrial function through bridging m5C RNA methylation

DNA methyltransferase 1 (DNMT1) is an enzyme known for DNA methylation maintenance. Point mutations in its replication focus targeting sequence (RFTS) domain lead to late-onset neurodegeneration, such as autosomal dominant cerebellar ataxia-deafness and narcolepsy (ADCA-DN) disorder. Here, we demonstrated that DNMT1 has the capability to bind to mRNA transcripts and facilitate 5-methylcytosine (m5C) RNA methylation by recruiting NOP2/Sun RNA methyltransferase 2 (NSUN2). RNA m5C methylation, in turn, promotes RNA stability for those genes modulating mitochondrial function. When the DNMT1 RFTS domain is mutated in mice, it triggers aberrant DNMT1-RNA interaction and significantly elevated m5C RNA methylation and RNA stability for a portion of metabolic genes. Consequently, increased levels of metabolic RNA transcripts contribute to cumulative oxidative stress, mitochondrial dysfunction, and neurological symptoms. Collectively, our results reveal a dual role of DNMT1 in regulating both DNA and RNA methylation, which further modulates mitochondrial function, shedding light on the pathogenic mechanism of DNMT1 mutation-induced neurodegeneration.

Chromosome-level genome assembly reveals adaptive evolution of the invasive Amazon sailfin catfish (Pterygoplichthys pardalis)

Catfish represents a diverse lineage with variable number of chromosomes and complex relationships with humans. Although certain species pose significant invasive threats to native fish populations, comprehensive genomic investigations into the evolutionary adaptations that contribute to their invasion success are lacking. To address this gap, our study presents a high-quality genome assembly of the Amazon sailfin catfish (Pterygoplichthys pardalis), a member of the armored catfish family, along with a comprehensive comparative genomic analysis. By utilizing conserved genomic regions across different catfish species, we reconstructed the 29 ancestral chromosomes of catfish, including two microchromosomes (28 and 29) that show different fusion and breakage patterns across species. Our analysis shows that the Amazon sailfin catfish genome is notably larger (1.58 Gb) with more than 40,000 coding genes. The genome expansion was linked to early repetitive sequence expansions and recent gene duplications. Several expanded genes are associated with immune functions, including antigen recognition domains like the Ig-v-set domain and the tandem expansion of the CD300 gene family. We also identified specific insertions in CNEs (conserved non-coding elements) near genes involved in cellular processes and neural development. Additionally, rapidly evolving and positively selected genes in the Amazon sailfin catfish genome were found to be associated with collagen formation. Moreover, we identified multiple positively selected codons in hoxb9, which may lead to functional alterations. These findings provide insights into molecular adaptations in an invasive catfish that may underlie its widespread invasion success.

Binding domain mutations provide insight into CTCF's relationship with chromatin and its contribution to gene regulation

Here we used a series of CTCF mutations to explore CTCF's relationship with chromatin and its contribution to gene regulation. CTCF's impact depends on the genomic context of bound sites and the unique binding properties of WT and mutant CTCF proteins. Specifically, CTCF's signal strength is linked to changes in accessibility, and the ability to block cohesin is linked to its binding stability. Multivariate modeling reveals that both CTCF and accessibility contribute independently to cohesin binding and insulation, but CTCF signal strength has a stronger effect. CTCF and chromatin have a bidirectional relationship such that at CTCF sites, accessibility is reduced in a cohesin-dependent, mutant-specific fashion. In addition, each mutant alters TF binding and accessibility in an indirect manner, changes which impart the most influence on rewiring transcriptional networks and the cell's ability to differentiate. Collectively, the mutant perturbations provide a rich resource for determining CTCF's site-specific effects.

Integrated promoter-capture Hi-C and Hi-C analysis reveals fine-tuned regulation of the 3D chromatin architecture in colorectal cancer

Introduction

Hi-C is a widely used technique for mapping chromosomal interactions within a 3D genomic framework, however, its resolution is often constrained by sequencing depth, making it challenging to detect fine-scale interactions. To overcome this limitation, Promoter-Capture Hi-C (PCHi-C), as it selectively enriches for promoter-associated interactions, was employed. This study integrates PCHi-C and Hi-C datasets from colorectal cancer (CRC) models investigate chromosomal interaction dynamics across various regulatory levels, from cis-regulatory elements to topologically associated domains (TADs). The primary goal is to examine how genomic structural alterations shape the epigenomic landscape in CRC and to assess their potential role in colorectal cancer susceptibility.

Methods

PCHi-C and Hi-C datasets from multiple colorectal cancer (CRC) studies were integrated to enhance the resolution of chromatin interaction mapping. The analysis focused on identifying fine-scale interactions within topologically associated domains (TADs) while incorporating histone modification landscapes (H3K27ac, H3K4me3) and transcriptomic signatures from CRC cell lines and the TCGA database. For experimental validation, ChIP-quantitative PCR was performed at the promoters of target genes using the highly malignant colorectal cell line HT29 and compared it to an embryonic cell line NT2D1.

Results

Our integrated analysis revealed significant genomic structural instability in CRC cells, closely associated with tumor-suppressive transcriptional programs. We identified nine dysregulated genes, including long non-coding RNAs (MALAT1, NEAT1, FTX, and PVT1), small nucleolar RNAs (SNORA26 and SNORA71A), and protein-coding genes (TMPRSS11D, TSPEAR, and DSG4), all of which exhibited a substantial increase in expression in CRC cell lines compared to human embryonic stem cells (hESCs). Additionally, we observed enriched activation-associated histone modifications (H3K27ac and H3K4me3) at the potential enhancer regions of these genes, indicating possible transcriptional activation. ChIP-quantitative PCRs conducted using in the highly malignant CRC cell line HT29, compared to the embryonic cell line NT2D1, further validated these findings, reinforcing the link between altered chromosomal interactions and gene dysregulation in CRC.

Discussion

This study sheds light on the dynamic 3D genome organization in CRC, highlighting critical structural changes associated with disease-associated loci. The identification of nine dysregulated genes points to potential biomarkers for colorectal cancer, with implications for diagnostic and therapeutic strategies. The combination of Hi-C and PCHi-C offers a refined approach for detecting chromosomal interactions at a higher resolution, laying the foundation for future studies on cancer-associated chromatin architecture.

Genome-wide CRISPR screen identifies IRF1 and TFAP4 as transcriptional regulators of Galectin-9 in T cell acute lymphoblastic leukemia

Galectin-9 is overexpressed in a variety of cancers and associated with worse clinical outcome in some cancers. However, the regulators driving Galectin-9 expression are unknown. Here, we defined the transcriptional regulators and epigenetic circuitry of Galectin-9 in pediatric T cell acute lymphoblastic leukemia (T-ALL), as an example of a disease with strong Galectin-9 expression, in which higher expression was associated with lower overall survival. By performing a genome-wide CRISPR screen, we identified the transcription factors IRF1 and TFAP4 as key regulators for Galectin-9 expression by binding its regulatory elements. Whereas IRF1 was observed exclusively on the promoter, TFAP4 binding was detected at an enhancer solely in T-ALL cells associated with higher Galectin-9 levels. Together, our results show that IRF1 is responsible and indispensable for Galectin-9 expression and TFAP4 further fine-tunes its expression. Our approach, a flow-based genome-wide CRISPR screen complemented by transcription factor binding and enhancer mapping, creates innovative opportunities for understanding and manipulating epigenetic transcriptional regulation in cancer.

A comparative genomic analysis at the chromosomal-level reveals evolutionary patterns of aphid chromosomes

Genomic rearrangements are primary drivers of evolution, promoting biodiversity. Aphids, an agricultural pest with high species diversity, exhibit rapid chromosomal evolution and diverse karyotypes. These variations have been attributed to their unique holocentric chromosomes and parthenogenesis, though this hypothesis has faced scrutiny. In this study, we generated a chromosomal-level reference genome assembly of the celery aphid (Semiaphis heraclei) and conducted comparative genomic analysis, revealing varying chromosomal evolution rates among aphid lineages, positively correlating with species diversity. Aphid X chromosomes have undergone frequent intra-chromosomal recombination, while autosomes show accelerated inter-chromosomal recombination. Moreover, considering both inter- and intra-chromosomal rearrangements, the increased autosomal rearrangement rates may be common across the Aphidomorpha. We identified that the expansion of DNA transposable elements and short interspersed nuclear elements (SINEs), coupled with gene loss and duplication associated with karyotypic instability (such as RIF1, BRD8, DMC1, and TERT), may play crucial roles in aphid chromosomal evolution. Additionally, our analysis revealed that the mutation and expansion of detoxification gene families in S. heraclei may be a key factor in adapting to host plant chemical defenses. Our results provide new insights into chromosomal evolutionary patterns and detoxification gene families evolution in aphids, aiding the understanding of species diversity and adaptive evolution.

Evidence for Fgf and Wnt regulation of Lhx2 during limb development via two limb-specific Lhx2-associated cis-regulatory modules

Introduction

In vertebrate limb morphogenesis, wingless-related integration site (Wnt) proteins and fibroblast growth factors (Fgfs) secreted from the apical ectodermal ridge (AER) coordinate proximodistal outgrowth. Fgfs also sustain sonic hedgehog (Shh) in the zone of polarizing activity (ZPA). Shh directs anteroposterior patterning and expansion and regulates AER-Fgfs, establishing a positive regulatory feedback loop that is vital in sustaining limb outgrowth. The transcription factor LIM homeodomain 2 (Lhx2) is expressed in the distal mesoderm and coordinates AER and ZPA signals that control cellular proliferation, differentiation, and shaping of the developing limb. Yet how Lhx2 is transcriptionally regulated to support such functions has only been partially characterized.

Methods/Results

We have identified two limb-specific cis-regulatory modules (CRMs) active within the Lhx2 expression domain in the limb. Chromatin conformation analysis of the Lhx2 locus in mouse embryonic limb bud cells predicted CRMs-Lhx2 promoter interactions. Single-cell RNA-sequencing analysis of limb bud cells revealed co-expression of several Fgf-related Ets and Wnt-related Tcf/Lef transcripts in Lhx2-expressing cells. Additionally, disruption of Ets and Tcf/Lef binding sites resulted in loss of reporter-driven CRM activity. Finally, binding of β-catenin to both Lhx2-associated CRMs supports the associated binding of Tcf/Lef transcription factors.

Discussion

These results suggest a role for Ets and Tcf/Lef transcription factors in the regulation of Lhx2 expression through these limb-specific Lhx2-associated CRMs. Moreover, these CRMs provide a mechanism for Fgf and Wnt signaling to localize and maintain distal Lhx2 expression during vertebrate limb development.

Binding domain mutations provide insight into CTCF's relationship with chromatin and its contribution to gene regulation

Here we used a series of CTCF mutations to explore CTCF's relationship with chromatin and its contribution to gene regulation. CTCF's impact depends on the genomic context of bound sites and the unique binding properties of WT and mutant CTCF proteins. Specifically, CTCF's signal strength is linked to changes in accessibility, and the ability to block cohesin is linked to its binding stability. Multivariate modelling reveals that both CTCF and accessibility contribute independently to cohesin binding and insulation, however CTCF signal strength has a stronger effect. CTCF and chromatin have a bidirectional relationship such that at CTCF sites, accessibility is reduced in a cohesin-dependent, mutant specific fashion. In addition, each mutant alters TF binding and accessibility in an indirect manner, changes which impart the most influence on rewiring transcriptional networks and the cell's ability to differentiate. Collectively, the mutant perturbations provide a rich resource for determining CTCF's site-specific effects.

Chromatin Topological Domains Associate With the Rapid Formation of Tandem Duplicates in Plants

In eukaryotes, chromatin is compacted within nuclei under the principle of compartmentalization. On top of that, condensin II establishes eukaryotic chromosome territories, while cohesin organizes the vertebrate genome by extruding chromatin loops and forming topologically associating domains (TADs). Thus far, the formation and roles of these chromatin structures in plants remain poorly understood. This study integrates Hi-C data from diverse plant species, demonstrating that nuclear DNA content influences large-scale chromosome conformation and affects the finer details of compartmental patterns. These contrasting compartmental patterns are distinguished by gene-to-gene loops and validated through cytological observations. Additionally, a novel chromatin domain type associated with tandem duplicate gene clusters is identified. These domains are independent of H3K27me3-mediated chromatin compartmentalization and exhibit evolutionary conservation across species. Gene pairs within TAD-like domains are younger and show higher levels of coexpression. These domains potentially promote the formation of tandem duplicates, a property appears unique to the Actinidia family. Overall, this study reveals functional chromatin domains in plants and provides evidence for the role of three-dimensional chromatin architecture in gene regulation and genome evolution.

Chromosome-level genome assemblies of sunflower oilseed and confectionery cultivars

The sunflower (Helianthus annuus L.), belonging to the Asteraceae family, is the world's fourth most important oil crop. Sunflower cultivars are categorized into oilseed and confectionery types. Here, we present chromosome-level genome assemblies of two Chinese sunflower cultivars-oilseed and confectionery-using PacBio HiFi and Hi-C sequencing. The oilseed cultivar, OXS, has a genome assembly spanning 3.03 Gb with 99.58% of sequences anchored to 17 chromosomes and a contig N50 length of 154.78 Mb. The first published confectionery cultivar genome, YDS, mirrors this closely with a 3.02 Gb assembly, contig N50 length of 153.87 Mb and 99.40% of sequences mapped similarly. Gene completeness reached 98.2% for OXS and 98.4% for YDS, with LTR Assembly Index scores of 24.73 and 25.85, respectively. Comparative genomics identified rapidly evolving gene families linked to synthesis, growth, and stress defense. Additionally, we found high collinearity between the YDS and OXS genomes, despite three significant inversions, and detected 15,056 large deletions and insertions. These findings lay a robust foundation for advanced genomic research and breeding innovations in sunflowers.

Hi-GDT: A Hi-C-based 3D gene domain analysis tool for analyzing local chromatin contacts in plants

BACKGROUND

Three-dimensional (3D) chromatin organization is emerging as a key factor in gene regulation in eukaryotes. Recent studies using high-resolution Hi-C analysis have explored fine-scale local chromatin contact domains in plants, as exemplified by the basic contact domains established at accessible gene border regions in Arabidopsis (Arabidopsis thaliana). However, we lack effective tools to identify these contact domains and examine their structural dynamics.

RESULTS

We developed the Hi-C-based 3D Gene Domain analysis Tool (Hi-GDT) to identify fine-scale local chromatin contact domains in plants, with a particular focus on gene borders. Hi-GDT successfully identifies local contact domains, including single-gene and multigene domains, with high reproducibility. Hi-GDT can also be used to discover local contact domains that are differentially organized in association with differences in gene expression between tissue types, genotypes, or in response to environmental stimuli.

CONCLUSIONS

Hi-GDT is a valuable tool for identifying genes regulated by dynamic 3D conformational changes, expanding our understanding of the structural and functional relevance of local 3D chromatin organization in plants. Hi-GDT is publicly available at https://github.com/CDL-HongwooLee/Hi-GDT.

Widespread 3D genome reorganization precedes programmed DNA rearrangement in Oxytricha trifallax

Genome organization recapitulates function, yet ciliates like Oxytricha trifallax possess highly-specialized germline genomes, which are largely transcriptionally silent. During post-zygotic development, Oxytricha's germline undergoes large-scale genome editing, rearranging precursor genome elements into a transcriptionally-active genome with thousands of gene-sized nanochromosomes. Transgenerationally-inherited RNAs, derived from the parental somatic genome, program the retention and reordering of germline fragments. Retained and eliminated DNA must be distinguished and processed separately, but the role of chromatin organization in this process is unknown. We developed tools for studying Oxytricha nuclei and apply them to map the 3D organization of precursor and developmental states using Hi-C. We find that the precursor conformation primes the germline for development, while a massive spatial reorganization during development differentiates retained from eliminated regions before DNA rearrangement. Further experiments suggest a role for RNA-DNA interactions and chromatin remodeling in this process, implying a critical role for 3D architecture in programmed genome rearrangement.

Super-silencer perturbation by EZH2 and REST inhibition leads to large loss of chromatin interactions and reduction in cancer growth

Human silencers have been shown to regulate developmental gene expression. However, the functional importance of human silencers needs to be elucidated, such as whether they can form 'super-silencers' and whether they are linked to cancer progression. Here, we show two silencer components of the FGF18 gene can cooperate through compensatory chromatin interactions to form a super-silencer. Double knockout of two silencers exhibited synergistic upregulation of FGF18 expression and changes in cell identity. To perturb the super-silencers, we applied combinational treatment of an enhancer of zeste homolog 2 inhibitor GSK343, and a repressor element 1-silencing transcription factor inhibitor, X5050 ('GR'). Interestingly, GR led to severe loss of topologically associated domains and loops, which were associated with reduced CTCF and TOP2A mRNA levels. Moreover, GR synergistically upregulated super-silencer-controlled genes related to cell cycle, apoptosis and DNA damage, leading to anticancer effects in vivo. Overall, our data demonstrated a super-silencer example and showed that GR can disrupt super-silencers, potentially leading to cancer ablation.

Mapping the 3D genome architecture

The spatial organization of the genome plays a critical role in regulating gene expression, cellular differentiation, and genome stability. This review provides an in-depth examination of the methodologies, computational tools, and frameworks developed to map the three-dimensional (3D) architecture of the genome, focusing on both ligation-based and ligation-free techniques. We also explore the limitations of these methods, including biases introduced by restriction enzyme digestion and ligation inefficiencies, and compare them to more recent ligation-free approaches such as Genome Architecture Mapping (GAM) and Split-Pool Recognition of Interactions by Tag Extension (SPRITE). These techniques offer unique insights into higher-order chromatin structures by bypassing ligation steps, thus enabling the capture of complex multi-way interactions that are often challenging to resolve with traditional methods. Furthermore, we discuss the integration of chromatin interaction data with other genomic layers through multimodal approaches, including recent advances in single-cell technologies like sci-HiC and scSPRITE, which help unravel the heterogeneity of chromatin architecture in development and disease.

EMF1 functions as a 3D chromatin modulator in Arabidopsis

It is well known that genome organizers, like mammalian CCCTC-binding factor (CTCF) or Drosophila architectural proteins CP190 and BEAF-32, contribute to the three-dimensional (3D) organization of the genome and ensure normal gene transcription. However, bona fide genome organizers have not been identified in plants. Here, we show that EMBRYONIC FLOWER1 (EMF1) functions as a genome modulator in Arabidopsis. EMF1 interacts with the cohesin component SISTER CHROMATIN COHESION3 (SCC3), and both proteins are enriched at compartment domain (CD) boundaries. Accordingly, emf1 and scc3 show a strength decrease at the CD boundary in which these proteins colocalize. EMF1 maintains CD boundary strength, either independently or in cooperation with histone modifications. Moreover, EMF1 is required to maintain gene-resolution interactions and to block long-range aberrant chromatin loops. These data unveil a key role of EMF1 in regulating 3D chromatin structure.

Sir2 is required for the quiescence-specific condensed three-dimensional chromatin structure of rDNA

Quiescence in Saccharomyces cerevisiae is a reversible G0 crucial for long-term survival under nutrient-deprived conditions. During quiescence, the genome is hypoacetylated and chromatin undergoes significant compaction. However, the 3D structure of the ribosomal DNA (rDNA) locus in this state is not well understood. Here, we report that the rDNA locus in quiescent cells forms a distinct condensed loop-like structure, different from structures observed during the mitotic cell cycle. Deletion of SIR2 disrupts this structure, causing it to collapse into a small dot and resulting in quiescence entry and exit defects. In contrast, Sir2 affects rDNA structure only modestly in G2/M phase. In the absence of Sir2, occupancy of both RNA Polymerase II and histone H3 increase at the rDNA locus during quiescence and through quiescence exit, further indicating gross defects in chromatin structure. Together, these results uncover a previously undescribed rDNA chromatin structure specific to quiescent cells and underscore the importance of Sir2 in facilitating the transition between cellular states.

Remodeling of Il4-Il13-Il5 locus underlies selective gene expression

The type 2 cytokines, interleukin (IL)-4, IL-13 and IL-5 reside within a multigene cluster. Both innate (ILC2) and adaptive T helper 2 (TH2) lymphocytes secrete type 2 cytokines with diverse production spectra. Using transcription factor footprint and chromatin accessibility, we systemically cataloged regulatory elements (REs) denoted as SHS-I/II, KHS-I/II, +6.5kbIl13, 5HS-I(a, b, c, d, e), 5HS-II and 5HS-III(a, b, c) across the extended Il4-Il13-Il5 locus in mice. Physical proximities among REs were coordinately remodeled in three-dimensional space after cell activation, leading to divergent compartmentalization of Il4, Il13 and Il5 with varied combinations of REs. Deletions of REs revealed no single RE solely accounted for selective regulation of a given cytokine in vivo. Instead, individual RE differentially contribute to proper genomic positioning of REs and target genes. RE deletions resulted in context-dependent dysregulation of cytokine expression and immune response in tissue. Thus, signal-dependent remodeling of three-dimensional configuration underlies divergent cytokine outputs from the type 2 loci.

RNA binding protein ZCCHC24 promotes tumorigenicity in triple-negative breast cancer

Triple-negative breast cancer (TNBC) lacks the expression of hormone and HER2 receptors and is highly malignant with no effective therapeutic targets. In TNBC, the cancer stem-like cell (CSC) population is considered to be the main cause of resistance to treatment. Thus, the therapeutic targeting of this population could substantially improve patient survival. Here, we identify the RNA-binding protein ZCCHC24 as enriched in the mesenchymal-like TNBC population. ZCCHC24 promotes the expression of a set of genes related to tumorigenicity and treatment resistance by directly binding to the cis-element "UGUWHWWA" in their mRNAs, thereby stabilizing them. One of the ZCCHC24 targets, ZEB1, is a transcription factor that promotes the expression of cancer stemness genes and reciprocally induces ZCCHC24 expression. ZCCHC24 knockdown by siRNAs shows a therapeutic effect and reduces the mesenchymal-like cell population in TNBC patient-derived xenografts. ZCCHC24 knockdown also has additive effects with the BET inhibitor JQ1 in suppressing tumor growth in TNBC patient-derived xenografts.

Integrative 3D genomics with multi-omics analysis and functional validation of genetic regulatory mechanisms of abdominal fat deposition in chickens

Chickens are the most abundant agricultural animals globally, with controlling abdominal fat deposition being a key objective in poultry breeding. While GWAS can identify genetic variants associated with abdominal fat deposition, the precise roles and mechanisms of these variants remain largely unclear. Here, we use male chickens from two lines divergently selected for abdominal fat deposition as experimental models. Through the integration of genomic, epigenomic, 3D genomic, and transcriptomic data, we build a comprehensive chromatin 3D regulatory network map to identify the genetic regulatory mechanisms that influence abdominal fat deposition in chickens. Notably, we find that the rs734209466 variant functions as an allele-specific enhancer, remotely enhancing the transcription of IGFBP2 and IGFBP5 by the binding transcription factor IRF4. This interaction influences the differentiation and proliferation of preadipocytes, which ultimately affects phenotype. This work presents a detailed genetic regulatory map for chicken abdominal fat deposition, offering molecular targets for selective breeding.

Heterochromatin protein 1 alpha (HP1α) undergoes a monomer to dimer transition that opens and compacts live cell genome architecture

Our understanding of heterochromatin nanostructure and its capacity to mediate gene silencing in a living cell has been prevented by the diffraction limit of optical microscopy. Thus, here to overcome this technical hurdle, and directly measure the nucleosome arrangement that underpins this dense chromatin state, we coupled fluorescence lifetime imaging microscopy (FLIM) of Förster resonance energy transfer (FRET) between histones core to the nucleosome, with molecular editing of heterochromatin protein 1 alpha (HP1α). Intriguingly, this super-resolved readout of nanoscale chromatin structure, alongside fluorescence fluctuation spectroscopy (FFS) and FLIM-FRET analysis of HP1α protein-protein interaction, revealed nucleosome arrangement to be differentially regulated by HP1α oligomeric state. Specifically, we found HP1α monomers to impart a previously undescribed global nucleosome spacing throughout genome architecture that is mediated by trimethylation on lysine 9 of histone H3 (H3K9me3) and locally reduced upon HP1α dimerisation. Collectively, these results demonstrate HP1α to impart a dual action on chromatin that increases the dynamic range of nucleosome proximity. We anticipate that this finding will have important implications for our understanding of how live cell heterochromatin structure regulates genome function.

The impact of the embryonic DNA methylation program on CTCF-mediated genome regulation

During mammalian embryogenesis, both the 5-cytosine DNA methylation (5meC) landscape and three dimensional (3D) chromatin architecture are profoundly remodeled during a process known as 'epigenetic reprogramming.' An understudied aspect of epigenetic reprogramming is how the 5meC flux, per se, affects the 3D genome. This is pertinent given the 5meC-sensitivity of DNA binding for a key regulator of chromosome folding: CTCF. We profiled the CTCF binding landscape using a mouse embryonic stem cell (ESC) differentiation protocol that models embryonic 5meC dynamics. Mouse ESCs lacking DNA methylation machinery are able to exit naive pluripotency, thus allowing for dissection of subtle effects of CTCF on gene expression. We performed CTCF HiChIP in both wild-type and mutant conditions to assess gained CTCF-CTCF contacts in the absence of 5meC. We performed H3K27ac HiChIP to determine the impact that ectopic CTCF binding has on cis-regulatory contacts. Using 5meC epigenome editing, we demonstrated that the methyl-mark is able to impair CTCF binding at select loci. Finally, a detailed dissection of the imprinted Zdbf2 locus showed how 5meC-antagonism of CTCF allows for proper gene regulation during differentiation. This work provides a comprehensive overview of how 5meC impacts the 3D genome in a relevant model for early embryonic events.

Congenital microcoria deletion in mouse links Sox21 dysregulation to disease and suggests a role for TGFB2 in glaucoma and myopia

Congenital microcoria (MCOR) is a rare hereditary developmental defect of the iris dilator muscle frequently associated with high axial myopia and high intraocular pressure (IOP) glaucoma. The condition is caused by submicroscopic rearrangements of chromosome 13q32.1. However, the mechanisms underlying the failure of iris development and the origin of associated features remain elusive. Here, we present a 3D architecture model of the 13q32.1 region, demonstrating that MCOR-related deletions consistently disrupt the boundary between two topologically associating domains (TADs). Deleting the critical MCOR-causing region in mice reveals ectopic Sox21 expression precisely aligning with Dct, each located in one of the two neighbor TADs. This observation is consistent with the TADs' boundary alteration and adoption of Dct regulatory elements by the Sox21 promoter. Additionally, we identify Tgfb2 as a target gene of SOX21 and show TGFΒ2 accumulation in the aqueous humor of an MCOR-affected subject. Accumulation of TGFB2 is recognized for its role in glaucoma and potential impact on axial myopia. Our results highlight the importance of SOX21-TGFB2 signaling in iris development and control of eye growth and IOP. Insights from MCOR studies may provide therapeutic avenues for this condition but also for glaucoma and high myopia conditions, affecting millions of people.

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.

Genome-wide analysis of the ERF Family in Stephania japonica provides insights into the regulatory role in Cepharanthine biosynthesis

Introduction

Cepharanthine (CEP), a bisbenzylisoquinoline alkaloid (bisBIA) extracted from Stephania japonica, has received significant attention for its anti-coronavirus properties. While ethylene response factors (ERFs) have been reported to regulate the biosynthesis of various alkaloids, their role in regulating CEP biosynthesis remains unexplored.

Methods

Genome-wide analysis of the ERF genes was performed with bioinformatics technology, and the expression patterns of different tissues, were analyzed by transcriptome sequencing analysis and real-time quantitative PCR verification. The nuclear-localized ERF gene cluster was shown to directly bind to the promoters of several CEP-associated genes, as demonstrated by yeast one-hybrid assays and subcellular localization assays.

Results

In this work, 59 SjERF genes were identified in the S. japonica genome and further categorized into ten subfamilies. Notably, a SjERF gene cluster containing three SjERF genes was found on chromosome 2. Yeast one-hybrid assays confirmed that the SjERF gene cluster can directly bind to the promoters of several CEP-associated genes, suggesting their crucial role in CEP metabolism. The SjERFs cluster-YFP fusion proteins were observed exclusively in the nuclei of Nicotiana benthamiana leaves. Tissue expression profiling revealed that 13 SjERFs exhibit high expression levels in the root, and the qRT-PCR results of six SjERFs were consistent with the RNA-Seq data. Furthermore, a co-expression network analysis demonstrated that 24 SjERFs were highly positively correlated with the contents of various alkaloids and expression levels of CEP biosynthetic genes.

Conclusion

This study provides the first systematic identification and analysis of ERF transcription factors in the S.japonica genome, laying the foundation for the future functional research of SjERFs transcription factors.

Light control of three-dimensional chromatin organization in soybean

Higher-order chromatin structure is critical for regulation of gene expression. In plants, light profoundly affects the morphogenesis of emerging seedlings as well as global gene expression to ensure optimal adaptation to environmental conditions. However, the changes and functional significance of chromatin organization in response to light during seedling development are not well documented. We constructed Hi-C contact maps for the cotyledon, apical hook and hypocotyl of soybean subjected to dark and light conditions. The resulting high-resolution Hi-C contact maps identified chromosome territories, A/B compartments, A/B sub-compartments, TADs (Topologically Associated Domains) and chromatin loops in each organ. We observed increased chromatin compaction under light and we found that domains that switched from B sub-compartments in darkness to A sub-compartments under light contained genes that were activated during photomorphogenesis. At the local scale, we identified a group of TADs constructed by gene clusters consisting of different numbers of Small Auxin-Upregulated RNAs (SAURs), which exhibited strict co-expression in the hook and hypocotyl in response to light stimulation. In the hypocotyl, RNA polymerase II (RNAPII) regulated the transcription of a SAURs cluster under light via TAD condensation. Our results suggest that the 3D genome is involved in the regulation of light-related gene expression in a tissue-specific manner.

ENT3C: an entropy-based similarity measure for Hi-C and micro-C derived contact matrices

Hi-C and micro-C sequencing have shed light on the profound importance of 3D genome organization in cellular function by probing 3D contact frequencies across the linear genome. The resulting contact matrices are extremely sparse and susceptible to technical- and sequence-based biases, making their comparison challenging. The development of reliable, robust and efficient methods for quantifying similarity between contact matrices is crucial for investigating variations in the 3D genome organization in different cell types or under different conditions, as well as evaluating experimental reproducibility. We present a novel method, ENT3C, which measures the change in pattern complexity in the vicinity of contact matrix diagonals to quantify their similarity. ENT3C provides a robust, user-friendly Hi-C or micro-C contact matrix similarity metric and a characteristic entropy signal that can be used to gain detailed biological insights into 3D genome organization.

Comparative genomics illuminates karyotype and sex chromosome evolution of sharks

Chondrichthyes is an important lineage to reconstruct the evolutionary history of vertebrates. Here, we analyzed genome synteny for six chondrichthyan chromosome-level genomes. Our comparative analysis reveals a slow evolutionary rate of chromosomal changes, with infrequent but independent fusions observed in sharks, skates, and chimaeras. The chondrichthyan common ancestor had a proto-vertebrate-like karyotype, including the presence of 18 microchromosome pairs. The X chromosome is a conversed microchromosome shared by all sharks, suggesting a likely common origin of the sex chromosome at least 181 million years ago. We characterized the Y chromosomes of two sharks that are highly differentiated from the X except for a small young evolutionary stratum and a small pseudoautosomal region. We found that shark sex chromosomes lack global dosage compensation but that dosage-sensitive genes are locally compensated. Our study on shark chromosome evolution enhances our understanding of shark sex chromosomes and vertebrate chromosome evolution.

Loss of multi-level 3D genome organization during breast cancer progression

Breast cancer entails intricate alterations in genome organization and expression. However, how three-dimensional (3D) chromatin structure changes in the progression from a normal to a breast cancer malignant state remains unknown. To address this, we conducted an analysis combining Hi-C data with lamina-associated domains (LADs), epigenomic marks, and gene expression in an in vitro model of breast cancer progression. Our results reveal that while the fundamental properties of topologically associating domains (TADs) are overall maintained, significant changes occur in the organization of compartments and subcompartments. These changes are closely correlated with alterations in the expression of oncogenic genes. We also observe a restructuring of TAD-TAD interactions, coinciding with a loss of spatial compartmentalization and radial positioning of the 3D genome. Notably, we identify a previously unrecognized interchromosomal insertion event, wherein a locus on chromosome 8 housing the MYC oncogene is inserted into a highly active subcompartment on chromosome 10. This insertion is accompanied by the formation of de novo enhancer contacts and activation of MYC, illustrating how structural genomic variants can alter the 3D genome to drive oncogenic states. In summary, our findings provide evidence for the loss of genome organization at multiple scales during breast cancer progression revealing novel relationships between genome 3D structure and oncogenic processes.

Transitions in chromatin conformation shaped by fatty acids and the circadian clock underlie hepatic transcriptional reorganization in obese mice

The circadian clock system coordinates metabolic, physiological, and behavioral functions across a 24-h cycle, crucial for adapting to environmental changes. Disruptions in circadian rhythms contribute to major metabolic pathologies like obesity and Type 2 diabetes. Understanding the regulatory mechanisms governing circadian control is vital for identifying therapeutic targets. It is well characterized that chromatin remodeling and 3D structure at genome regulatory elements contributes to circadian transcriptional cycles; yet the impact of rhythmic chromatin topology in metabolic disease is largely unexplored. In this study, we explore how the spatial configuration of the genome adapts to diet, rewiring circadian transcription and contributing to dysfunctional metabolism. We describe daily fluctuations in chromatin contacts between distal regulatory elements of metabolic control genes in livers from lean and obese mice and identify specific lipid-responsive regions recruiting the clock molecular machinery. Interestingly, under high-fat feeding, a distinct interactome for the clock-controlled gene Dbp strategically promotes the expression of distal metabolic genes including Fgf21. Alongside, new chromatin loops between regulatory elements from genes involved in lipid metabolism control contribute to their transcriptional activation. These enhancers are responsive to lipids through CEBPβ, counteracting the circadian repressor REVERBa. Our findings highlight the intricate coupling of circadian gene expression to a dynamic nuclear environment under high-fat feeding, supporting a temporally regulated program of gene expression and transcriptional adaptation to diet.

Brain and cancer associated binding domain mutations provide insight into CTCF's relationship with chromatin and its ability to act as a chromatin organizer

Although only a fraction of CTCF motifs are bound in any cell type, and approximately half of the occupied sites overlap cohesin, the mechanisms underlying cell-type specific attachment and ability to function as a chromatin organizer remain unknown. To investigate the relationship between CTCF and chromatin we applied a combination of imaging, structural and molecular approaches, using a series of brain and cancer associated CTCF mutations that act as CTCF perturbations. We demonstrate that binding and the functional impact of WT and mutant CTCF depend not only on the unique properties of each protein, but also on the genomic context of bound sites. Our studies also highlight the reciprocal relationship between CTCF and chromatin, demonstrating that the unique binding properties of WT and mutant proteins have a distinct impact on accessibility, TF binding, cohesin overlap, chromatin interactivity and gene expression programs, providing insight into their cancer and brain related effects.

DiffGR: Detecting Differentially Interacting Genomic Regions from Hi-C Contact Maps

Recent advances in high-throughput chromosome conformation capture (Hi-C) techniques have allowed us to map genome-wide chromatin interactions and uncover higher-order chromatin structures, thereby shedding light on the principles of genome architecture and functions. However, statistical methods for detecting changes in large-scale chromatin organization such as topologically associating domains (TADs) are still lacking. Here, we proposed a new statistical method, DiffGR, for detecting differentially interacting genomic regions at the TAD level between Hi-C contact maps. We utilized the stratum-adjusted correlation coefficient to measure similarity of local TAD regions. We then developed a nonparametric approach to identify statistically significant changes of genomic interacting regions. Through simulation studies, we demonstrated that DiffGR can robustly and effectively discover differential genomic regions under various conditions. Furthermore, we successfully revealed cell type-specific changes in genomic interacting regions in both human and mouse Hi-C datasets, and illustrated that DiffGR yielded consistent and advantageous results compared with state-of-the-art differential TAD detection methods. The DiffGR R package is published under the GNU General Public License (GPL) ≥ 2 license and is publicly available at https://github.com/wmalab/DiffGR.

An improved genome assembly of Chrysanthemum nankingense reveals expansion and functional diversification of terpene synthase gene family

BACKGROUND

Terpenes are important components of plant aromas, and terpene synthases (TPSs) are the key enzymes driving terpene diversification. In this study, we characterized the volatile terpenes in five different Chrysanthemum nankingense tissues. In addition, genome-wide identification and expression analysis of TPS genes was conducted utilizing an improved chromosome-scale genome assembly and tissue-specific transcriptomes. The biochemical functions of three representative TPSs were also investigated.

RESULTS

We identified tissue-specific volatile organic compound (VOC) and volatile terpene profiles. The improved Chrysanthemum nankingense genome assembly was high-quality, including a larger assembled size (3.26 Gb) and a better contig N50 length (3.18 Mb) compared to the old version. A total of 140 CnTPS genes were identified, with the majority representing the TPS-a and TPS-b subfamilies. The chromosomal distribution of these TPS genes was uneven, and 26 genes were included in biosynthetic gene clusters. Closely-related Chrysanthemum taxa were also found to contain diverse TPS genes, and the expression profiles of most CnTPSs were tissue-specific. The three investigated CnTPS enzymes exhibited versatile activities, suggesting multifunctionality.

CONCLUSIONS

We systematically characterized the structure and diversity of TPS genes across the Chrysanthemum nankingense genome, as well as the potential biochemical functions of representative genes. Our results provide a basis for future studies of terpene biosynthesis in chrysanthemums, as well as for the breeding of improved chrysanthemum varieties.

Defining a TFAP2C-centered transcription factor network during murine peri-implantation

Transcription factors (TFs) play important roles in early embryonic development, but factors regulating TF action, relationships in signaling cascade, genome-wide localizations, and impacts on cell fate transitions during this process have not been clearly elucidated. In this study, we used uliCUT&RUN-seq to delineate a TFAP2C-centered regulatory network, showing that it involves promoter-enhancer interactions and regulates TEAD4 and KLF5 function to mediate cell polarization. Notably, we found that maternal retinoic acid metabolism regulates TFAP2C expression and function by inducing the active demethylation of SINEs, indicating that the RARG-TFAP2C-TEAD4/KLF5 axis connects the maternal-to-zygotic transition to polarization. Moreover, we found that both genomic imprinting and SNP-transferred genetic information can influence TF positioning to regulate parental gene expressions in a sophisticated manner. In summary, we propose a ternary model of TF regulation in murine embryonic development with TFAP2C as the core element and metabolic, epigenetic, and genetic information as nodes connecting the pathways.

Hi-Tag: a simple and efficient method for identifying protein-mediated long-range chromatin interactions with low cell numbers

Protein-mediated chromatin interactions can be revealed by coupling proximity-based ligation with chromatin immunoprecipitation. However, these techniques require complex experimental procedures and millions of cells per experiment, which limits their widespread application in life science research. Here, we develop a novel method, Hi-Tag, that identifies high-resolution, long-range chromatin interactions through transposase tagmentation and chromatin proximity ligation (with a phosphorothioate-modified linker). Hi-Tag can be implemented using as few as 100,000 cells, involving simple experimental procedures that can be completed within 1.5 days. Meanwhile, Hi-Tag is capable of using its own data to identify the binding sites of specific proteins, based on which, it can acquire accurate interaction information. Our results suggest that Hi-Tag has great potential for advancing chromatin interaction studies, particularly in the context of limited cell availability.

Pairtools: From sequencing data to chromosome contacts

The field of 3D genome organization produces large amounts of sequencing data from Hi-C and a rapidly-expanding set of other chromosome conformation protocols (3C+). Massive and heterogeneous 3C+ data require high-performance and flexible processing of sequenced reads into contact pairs. To meet these challenges, we present pairtools-a flexible suite of tools for contact extraction from sequencing data. Pairtools provides modular command-line interface (CLI) tools that can be flexibly chained into data processing pipelines. The core operations provided by pairtools are parsing of.sam alignments into Hi-C pairs, sorting and removal of PCR duplicates. In addition, pairtools provides auxiliary tools for building feature-rich 3C+ pipelines, including contact pair manipulation, filtration, and quality control. Benchmarking pairtools against popular 3C+ data pipelines shows advantages of pairtools for high-performance and flexible 3C+ analysis. Finally, pairtools provides protocol-specific tools for restriction-based protocols, haplotype-resolved contacts, and single-cell Hi-C. The combination of CLI tools and tight integration with Python data analysis libraries makes pairtools a versatile foundation for a broad range of 3C+ pipelines.

TEAD2 initiates ground-state pluripotency by mediating chromatin looping

The transition of mouse embryonic stem cells (ESCs) between serum/LIF and 2i(MEK and GSK3 kinase inhibitor)/LIF culture conditions serves as a valuable model for exploring the mechanisms underlying ground and confused pluripotent states. Regulatory networks comprising core and ancillary pluripotency factors drive the gene expression programs defining stable naïve pluripotency. In our study, we systematically screened factors essential for ESC pluripotency, identifying TEAD2 as an ancillary factor maintaining ground-state pluripotency in 2i/LIF ESCs and facilitating the transition from serum/LIF to 2i/LIF ESCs. TEAD2 exhibits increased binding to chromatin in 2i/LIF ESCs, targeting active chromatin regions to regulate the expression of 2i-specific genes. In addition, TEAD2 facilitates the expression of 2i-specific genes by mediating enhancer-promoter interactions during the serum/LIF to 2i/LIF transition. Notably, deletion of Tead2 results in reduction of a specific set of enhancer-promoter interactions without significantly affecting binding of chromatin architecture proteins, CCCTC-binding factor (CTCF), and Yin Yang 1 (YY1). In summary, our findings highlight a novel prominent role of TEAD2 in orchestrating higher-order chromatin structures of 2i-specific genes to sustain ground-state pluripotency.

Tet-mediated DNA methylation dynamics affect chromosome organization

DNA Methylation is a significant epigenetic modification that can modulate chromosome states, but its role in orchestrating chromosome organization has not been well elucidated. Here we systematically assessed the effects of DNA Methylation on chromosome organization with a multi-omics strategy to capture DNA Methylation and high-order chromosome interaction simultaneously on mouse embryonic stem cells with DNA methylation dioxygenase Tet triple knock-out (Tet-TKO). Globally, upon Tet-TKO, we observed weakened compartmentalization, corresponding to decreased methylation differences between CpG island (CGI) rich and poor domains. Tet-TKO could also induce hypermethylation for the CTCF binding peaks in TAD boundaries and chromatin loop anchors. Accordingly, CTCF peak generally weakened upon Tet-TKO, which results in weakened TAD structure and depletion of long-range chromatin loops. Genes that lost enhancer-promoter looping upon Tet-TKO showed DNA hypermethylation in their gene bodies, which may compensate for the disruption of gene expression. We also observed distinct effects of Tet1 and Tet2 on chromatin organization and increased DNA methylation correlation on spatially interacted fragments upon Tet inactivation. Our work showed the broad effects of Tet inactivation and DNA methylation dynamics on chromosome organization.

Chromatin gene-gene loops support the cross-regulation of genes with related function

Chromatin loops between gene pairs have been observed in diverse contexts in both flies and vertebrates. Combining high-resolution Capture-C, DNA fluorescence in situ hybridization, and genetic perturbations, we dissect the functional role of three loops between genes with related function during Drosophila embryogenesis. By mutating the loop anchor (but not the gene) or the gene (but not loop anchor), we disentangle loop formation and gene expression and show that the 3D proximity of paralogous gene loci supports their co-regulation. Breaking the loop leads to either an attenuation or enhancement of expression and perturbs their relative levels of expression and cross-regulation. Although many loops appear constitutive across embryogenesis, their function can change in different developmental contexts. Taken together, our results indicate that chromatin gene-gene loops act as architectural scaffolds that can be used in different ways in different contexts to fine-tune the coordinated expression of genes with related functions and sustain their cross-regulation.

BL-Hi-C reveals the 3D genome structure of Brassica crops with high sensitivity

High-throughput Chromatin Conformation Capture (Hi-C) technologies can be used to investigate the three-dimensional genomic structure of plants. However, the practical utility of these technologies is impeded by significant background noise, hindering their capability in detecting fine 3D genomic structures. In this study, we optimized the Bridge Linker Hi-C technology (BL-Hi-C) to comprehensively investigate the 3D chromatin landscape of Brassica rapa and Brassica oleracea. The Bouquet configuration of both B. rapa and B. oleracea was elucidated through the construction of a 3D genome simulation. The optimized BL-Hi-C exhibited lower background noise compared to conventional Hi-C methods. Taking this advantage, we used BL-Hi-C to identify FLC gene loops in Arabidopsis, B. rapa, and B. oleracea. We observed that gene loops of FLC2 exhibited conservation across Arabidopsis, B. rapa, and B. oleracea. While gene loops of syntenic FLCs exhibited conservation across B. rapa and B. oleracea, variations in gene loops were evident among multiple paralogs FLCs within the same species. Collectively, our findings highlight the high sensitivity of optimized BL-Hi-C as a powerful tool for investigating the fine 3D genomic organization.

Cepharanthine analogs mining and genomes of Stephania accelerate anti-coronavirus drug discovery

Cepharanthine is a secondary metabolite isolated from Stephania. It has been reported that it has anti-conronaviruses activities including severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). Here, we assemble three Stephania genomes (S. japonica, S. yunnanensis, and S. cepharantha), propose the cepharanthine biosynthetic pathway, and assess the antiviral potential of compounds involved in the pathway. Among the three genomes, S. japonica has a near telomere-to-telomere assembly with one remaining gap, and S. cepharantha and S. yunnanensis have chromosome-level assemblies. Following by biosynthetic gene mining and metabolomics analysis, we identify seven cepharanthine analogs that have broad-spectrum anti-coronavirus activities, including SARS-CoV-2, Guangxi pangolin-CoV (GX_P2V), swine acute diarrhoea syndrome coronavirus (SADS-CoV), and porcine epidemic diarrhea virus (PEDV). We also show that two other genera, Nelumbo and Thalictrum, can produce cepharanthine analogs, and thus have the potential for antiviral compound discovery. Results generated from this study could accelerate broad-spectrum anti-coronavirus drug discovery.

Increased long-distance and homo-trans interactions related to H3K27me3 in Arabidopsis hybrids

In plants, the genome structure of hybrids changes compared with their parents, but the effects of these changes in hybrids remain elusive. Comparing reciprocal crosses between Col × C24 and C24 × Col in Arabidopsis using high-throughput chromosome conformation capture assay (Hi-C) analysis, we found that hybrid three-dimensional (3D) chromatin organization had more long-distance interactions relative to parents, and this was mainly located in promoter regions and enriched in genes with heterosis-related pathways. The interactions between euchromatin and heterochromatin were increased, and the compartment strength decreased in hybrids. In compartment domain (CD) boundaries, the distal interactions were more in hybrids than their parents. In the hybrids of CURLY LEAF (clf) mutants clfCol  × clfC24 and clfC24  × clfCol , the heterosis phenotype was damaged, and the long-distance interactions in hybrids were fewer than in their parents with lower H3K27me3. ChIP-seq data revealed higher levels of H3K27me3 in the region adjacent to the CD boundary and the same interactional homo-trans sites in the wild-type (WT) hybrids, which may have led to more long-distance interactions. In addition, the differentially expressed genes (DEGs) located in the boundaries of CDs and loop regions changed obviously in WT, and the functional enrichment for DEGs was different between WT and clf in the long-distance interactions and loop regions. Our findings may therefore propose a new epigenetic explanation of heterosis in the Arabidopsis hybrids and provide new insights into crop breeding and yield increase.

Genomic evolution of island birds from the view of the Swinhoe's pheasant (Lophura swinhoii)

Island endemic birds account for the majority of extinct vertebrates in the past few centuries. To date, the evolutionary characteristics of island endemic bird's is poorly known. In this research, we de novo assembled a high-quality chromosome-level reference genome for the Swinhoe's pheasant, which is a typical endemic island bird. Results of collinearity tests suggest rapid ancient chromosome rearrangement that may have contributed to the initial species radiation within Phasianidae, and a role for the insertions of CR1 transposable elements in rearranging chromosomes in Phasianidae. During the evolution of the Swinhoe's pheasant, natural selection positively selected genes involved in fecundity and body size functions, at both the species and population levels, which reflect genetic variation associated with island adaptation. We further tested for variation in population genomic traits between the Swinhoe's pheasant and its phylogenetically closely related mainland relative the silver pheasant, and found higher levels of genetic drift and inbreeding in the Swinhoe's pheasant genome. Divergent demographic histories of insular and mainland bird species during the last glacial period may reflect the differing impact of insular and continental climates on the evolution of species. Our research interprets the natural history and population genetic characteristics of the insular endemic bird the Swinhoe's pheasant, at a genome-wide scale, provides a broader perspective on insular speciation, and adaptive evolution and contributes to the genetic conservation of island endemic birds.

Mapping nucleosome-resolution chromatin organization and enhancer-promoter loops in plants using Micro-C-XL

Although chromatin organizations in plants have been dissected at the scales of compartments and topologically associating domain (TAD)-like domains, there remains a gap in resolving fine-scale structures. Here, we use Micro-C-XL, a high-throughput chromosome conformation capture (Hi-C)-based technology that involves micrococcal nuclease (instead of restriction enzymes) and long cross-linkers, to dissect single nucleosome-resolution chromatin organization in Arabidopsis. Insulation analysis reveals more than 14,000 boundaries, which mostly include chromatin accessibility, epigenetic modifications, and transcription factors. Micro-C-XL reveals associations between RNA Pols and local chromatin organizations, suggesting that gene transcription substantially contributes to the establishment of local chromatin domains. By perturbing Pol II both genetically and chemically at the gene level, we confirm its function in regulating chromatin organization. Visible loops and stripes are assigned to super-enhancers and their targeted genes, thus providing direct insights for the identification and mechanistic analysis of distal CREs and their working modes in plants. We further investigate possible factors regulating these chromatin loops. Subsequently, we expand Micro-C-XL to soybean and rice. In summary, we use Micro-C-XL for analyses of plants, which reveal fine-scale chromatin organization and enhancer-promoter loops and provide insights regarding three-dimensional genomes in plants.

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.

Chromatin remodeling analysis reveals the RdDM pathway responds to low-phosphorus stress in maize

Chromatin in eukaryotes folds into a complex three-dimensional (3D) structure that is essential for controlling gene expression and cellular function and is dynamically regulated in biological processes. Studies on plant phosphorus signaling have concentrated on single genes and gene interactions. It is critical to expand the existing signaling pathway in terms of its 3D structure. In this study, low-Pi treatment led to greater chromatin volume. Furthermore, low-Pi stress increased the insulation score and the number of TAD-like domains, but the effects on the A/B compartment were not obvious. The methylation levels of target sites (hereafter as RdDM levels) peaked at specific TAD-like boundaries, whereas RdDM peak levels at conserved TAD-like boundaries shifted and decreased sharply. The distribution pattern of RdDM sites originating from the Helitron transposons matched that of genome-wide RdDM sites near TAD-like boundaries. RdDM pathway genes were upregulated in the middle or early stages and downregulated in the later stages under low-Pi conditions. The RdDM pathway mutant ddm1a showed increased tolerance to low-Pi stress, with shortened and thickened roots contributing to higher Pi uptake from the shallow soil layer. ChIP-seq results revealed that ZmDDM1A could bind to Pi- and root development-related genes. Strong associations were found between interacting genes in significantly different chromatin-interaction regions and root traits. These findings not only expand the mechanisms by which plants respond to low-Pi stress through the RdDM pathway but also offer a crucial framework for the analysis of biological issues using 3D genomics.