Mechanisms of enhancer action: the known and the unknown

Synergistic and antagonistic activities of IRF8 and FOS enhancer pairs during an immune-cell fate switch

Cell fate instructive genes tend to be regulated by large clusters of enhancers. Whether and how individual enhancers within such clusters cooperate in regulating gene expression is poorly understood. We have previously developed a computational method, SEGCOND, which identifies hubs that we termed Putative Transcriptional Condensates (PTCs), consisting of enhancer clusters and associated target genes. Here, we use SEGCOND to identify PTCs in a CEBPA-induced B-cell-to-macrophage transdifferentiation system. We find that PTCs are enriched for highly expressed, lineage-restricted genes and associate with BRD4, a component of transcriptional condensates. Further, we performed single and combinatorial deletions of enhancers within two PTCs active during induced transdifferentiation, harboring IRF8 and FOS. Two enhancers within the IRF8 PTC were found to provide a backup mechanism when combined, safeguarding IRF8 expression and efficient transdifferentiation. Unexpectedly, two individual enhancers within the FOS PTC antagonize each other on day 1 of transdifferentiation, delaying the conversion of B-cells into macrophages and reducing FOS expression, while on day 7, they cooperate to increase FOS levels induced cells. Our results reveal complex, differentiation-stage-specific interactions between individual enhancers within enhancer clusters.

Enhancer RNA transcription pinpoints functional genetic variants linked to asthma

Bidirectional enhancer RNA (eRNA) transcription is a widespread response to environmental signals and glucocorticoids. We investigated whether single nucleotide polymorphisms (SNPs) within dynamically regulated eRNA-transcribing regions contribute to genetic variation in asthma. Through applying multivariate regression modeling with permutation-based significance thresholding to a large clinical cohort, we identified novel associations between asthma and 35 SNPs located in eRNA-transcribing regions implicated in regulating cellular processes relevant to asthma, including rs258760 (mean allele frequency = 0.34, asthma odds ratio = 0.95; P = 5.04E-03). We show that rs258760 disrupts an active aryl hydrocarbon receptor (AHR) response element linked to transcriptional regulation of the glucocorticoid receptor gene by AHR ligands, which are commonly found in combusted air pollution. The role of rs258760 as a protective variant for asthma was independently validated using UK Biobank data. Our findings establish eRNA signatures as a tool for discovery of functional genetic variants and define a novel association between air pollution, glucocorticoid signaling and asthma.

Pre-existing DNA methylation signatures in the prefrontal cortex of alcohol-naïve nonhuman primates define neural vulnerability for future risky ethanol consumption

Alcohol use disorder (AUD) is a highly prevalent, complex, multifactorial and heterogeneous disorder, with 11 % and 30 % of adults meeting criteria for past-year and lifetime AUD, respectively. Identification of the molecular mechanisms underlying risk for AUD would facilitate effective deployment of personalized interventions. Studies using rhesus monkeys and rats, have demonstrated that individuals with low cognitive flexibility and a predisposition towards habitual behaviors show an increased risk for future heavy drinking. Further, low cognitive flexibility is associated with reduced dorsolateral prefrontal cortex (dlPFC) function in rhesus monkeys. To explore the underlying unique molecular signatures that increase risk for chronic heavy drinking, a genome-wide DNA methylation (DNAm) analysis of the alcohol-naïve dlPFC-A46 biopsy prior to chronic alcohol self-administration was conducted. The DNAm profile provides a molecular snapshot of the alcohol-naïve dlPFC, with mapped genes and associated signaling pathways that vary across individuals. The analysis identified 1463 differentially methylated regions (DMRs) related to unique genes that were strongly associated with average ethanol intake consumed over 6 months of voluntary self-administration. These findings translate behavioral phenotypes into neural markers of risk for AUD, and hold promise for parallel discoveries in risk for other disorders involving impaired cognitive flexibility. SIGNIFICANCE: Alcohol use disorder (AUD) is a highly prevalent and heterogeneous disorder. Prevention strategies to accurately identify individuals with a high risk for AUD, would help reduce the prevalence, and severity of AUD. Our novel epigenomic analysis of the alcohol-naïve nonhuman primate cortex provides a molecular snapshot of the vulnerable brain, pointing to circuitry and molecular mechanisms associated with cortical development, synaptic functions, glutamatergic signaling and coordinated signaling pathways. With a complex disorder like AUD, having the ability to identify the underlying molecular mechanisms underlying AUD risk is critical for better development of personalized effective treatments.

Genomic regions occupied by both RARα and VDR are involved in the convergence and cooperation of retinoid and vitamin D signaling pathways

Retinoic acid receptors (RARs) and the vitamin D receptor (VDR) regulate distinct but overlapping gene sets in multiple cell types. The abundance and characteristics of regulatory regions, occupied by both RARs and VDR are largely unexplored. We used global approaches (ChIP-seq, RNA-seq, and ATAC-seq) and bioinformatics tools to map and characterize common binding regions of RARα and VDR in differentiated human THP-1 cells. We found that the cistromes of ligand-activated RARα and VDR largely overlapped, and their agonists (AM580 and calcitriol) co-regulated several genes, often cooperatively. Common binding regions were frequently (but not exclusively) annotated with co-regulated genes and exhibited increased MED1 occupancy upon ligand stimulation, suggesting their involvement in gene regulation. Chromatin accessibility was typically higher in the common regions than in regions occupied exclusively by RARα or VDR. DNA response elements for RARα (DR1/2/5) and VDR (DR3) were enriched in the common regions, albeit the co-occurrence of the two types of canonical motifs was low (8.4%), suggesting that "degenerate" DR1/2/5 and DR3 motifs or other sequences could mediate the binding. In summary, common binding regions of RARα and VDR are at the crossroads of the retinoid and vitamin D pathways, playing important roles in their convergence and cooperation.

Spatial genomics of AAV vectors reveals mechanism of transcriptional crosstalk that enables targeted delivery of large genetic cargo

Cell-type-specific regulatory elements such as enhancers can direct expression of recombinant adeno-associated viruses (AAVs) to specific cell types, but this approach is limited by the relatively small packaging capacity of AAVs. In this study, we used spatial genomics to show that transcriptional crosstalk between individual AAV genomes provides a general method for cell-type-specific expression of large cargo by separating distally acting regulatory elements into a second AAV genome. We identified and profiled transcriptional crosstalk in AAV genomes carrying 11 different enhancers active in mouse brain. We developed spatial genomics methods to identify and localize AAV genomes and their concatemeric forms in cultured cells and in tissue, and we demonstrate here that transcriptional crosstalk is dependent upon concatemer formation. Finally, we leveraged transcriptional crosstalk to drive expression of a 3.2-kb Cas9 cargo in a cell-type-specific manner with systemically administered engineered AAVs, and we demonstrate AAV-delivered, minimally invasive, cell-type-specific gene editing in wild-type mice that recapitulates known disease phenotypes.

BmNPV interacts with super-enhancer regions of the host chromatin to hijack cellular transcription machinery

Effective transcriptional activation relies on the spatial interaction between specific DNA elements. DNA interactions have also been observed between DNA viruses and their hosts, with limited understanding of the involved details. Baculovirus is a representative species of DNA virus and has been reported to interact with the host genome in our previous study. However, the biological significance of the baculovirus-host trans-species DNA interaction and its underlying mechanisms remain elusive. Here, using Bombyx mori nucleopolyhedrovirus (BmNPV) as the model virus, we combine epigenome, transcriptome, and biochemical assays to investigate the baculovirus-host DNA interaction. Our data show that BmNPV hijacks the transcriptional regulatory capacity of host super-enhancers (SEs) by physically interacting with these regions on the host genome. This results in the usurpation of the activating capacity of an SE-binding transcription factor GATA by the virus, thereby impairing the SE-induced specific transcriptional activation of the target antiviral genes. Moreover, the hijacked regulatory capacity is spread on BmNPV genome through cis-interaction of viral DNA, leading to enhanced viral gene expression. Overall, our results provide novel insights into the intricate interplay of viruses with host gene expression regulatory networks and broaden the vision in the mechanisms of viral exploitation on cellular machinery.

Genomic Language Model for Predicting Enhancers and Their Allele-Specific Activity in the Human Genome

Predicting and deciphering the regulatory logic of enhancers is a challenging problem, due to the intricate sequence features and lack of consistent genetic or epigenetic signatures that can accurately discriminate enhancers from other genomic regions. Recent machine-learning based methods have spotlighted the importance of extracting nucleotide composition of enhancers but failed to learn the sequence context and perform suboptimally. Motivated by advances in genomic language models, we developed DNABERT-Enhancer, a novel enhancer prediction method, by applying DNABERT pre-trained language model on the human genome. We trained two different models, using large collection of enhancers curated from the ENCODE registry of candidate cis-Regulatory Elements. The best fine-tuned model achieved 88.05% accuracy with Matthews correlation coefficient of 76% on independent set aside data. Further, we present the analysis of the predicted enhancers for all chromosomes of the human genome by comparing with the enhancer regions reported in publicly available databases. Finally, we applied DNABERT-Enhancer along with other DNABERT based regulatory genomic region prediction models to predict candidate SNPs with allele-specific enhancer and transcription factor binding activity. The genome-wide enhancer annotations and candidate loss-of-function genetic variants predicted by DNABERT-Enhancer provide valuable resources for genome interpretation in functional and clinical genomics studies.

Unraveling the intricate molecular landscape and potential biomarkers in lung adenocarcinoma through integrative epigenomic and transcriptomic profiling

Lung adenocarcinoma (LUAD) remains a leading cause of cancer-related mortalities, characterized by substantial genetic heterogeneity that challenges a comprehensive understanding of its progression. This study employs next-generation sequencing data analysis to transform our comprehension of LUAD pathogenesis. Integrating epigenetic and transcriptomic data of LUAD patients, this approach assessed the critical regulatory occurrences, identified therapeutic targets, and offered profound insights into cancer molecular foundations. We employed the DNA methylation data to identify differentially methylated CpG sites and explored the transcriptome profiles of their adjacent genes. An intersectional analysis of gene expression profiles uncovered 419 differentially expressed genes (DEGs) influenced by smoke-induced differential DNA methylation, among which hub genes, including mitochondrial ribosomal proteins (MRPs), and ribosomal proteins (RPs) such as MRPS15, MRPS5, MRPL33, RPL24, RPL7L1, MRPL15, TUFM, MRPL22, and RSL1D1, were identified using a network-based approach. These hub genes were overexpressed and enriched to RNA processing, ribosome biogenesis, and mitochondrial translation, which is critical in LUAD progression. Enhancer Linking Methylation/Expression Relationship (ELMER) analysis revealed transcription factor (TF) binding motifs, such as JUN, NKX23, FOSB, RUNX3, and FOSL1, which regulated these hub genes through methylation-dependent enhancer dynamics. Predominant hypomethylation of MRPs and RPs disrupted mitochondrial function, contributed to oxidative phosphorylation (OXPHOS) and metabolic reprogramming, favoring cancer cell survival. The survival analysis validated the clinical relevance of these hub genes, with high-expression cohorts exhibiting poor overall survival (OS) outcomes enlightened their relevance in LUAD pathogenesis and presented the potential for developing novel targeted therapeutic strategies.

Enhancing our understanding of endothelial cells

What determines whether an endothelial cell becomes part of an artery, a vein or a capillary?

Comprehensive transcriptional regulatory networks in potato through chromatin accessibility and transcriptome under drought and salt stresses

Drought and high salt stress have a great negative impact on potato growth and development. However, the molecular mechanisms by which different tissues and organs of potato plants respond to drought and high salt stress at different stress times lack definition. In this study, we mapped the whole genome of THSs in potato in response to different stresses using RNA-seq and ATAC-seq technologies and constructed the unique and shared transcriptional regulatory networks (TRNs) under different stresses, stress time points, and tissues in potato. The results showed opposite trends for changes in chromatin accessibility and expression of genes under drought and salt stresses. Forty-eight hours and root-specific TRNs were more complex than those of 3 h and leaf, and there were genes with inconsistent drought- and salt-stress-regulated expression only in root-shared TRNs, demonstrating the variability of potato's response to stresses under different tissues and treatment times. These results provide a basis for elucidating the transcriptional mechanisms underlying the specific response of potato to drought or salt stress and the common response to salt and drought stress.

Single-cell multiomics reveals a gene regulatory circuit driving leukemia cell differentiation

Cancer differentiation therapy aims to induce the maturation of neoplastic cells, but the mechanisms regulating cell fate decisions in oncogenic contexts remain unclear. In this study, we integrated single-cell chromatin accessibility and single-cell transcriptome analyses to explore the regulatory trajectories of a classical PML/RARα+ acute promyeloid leukemia (APL) cell line (NB4) post treatment by all-trans-retinoid acid (ATRA). Our findings indicated that ATRA activated specific PML/RARα-target enhancers to trigger a regulatory circuit composed of a positive feedforward gene regulatory circuit involving two transcription factors, SPI1 and CEBPE. This regulatory circuit was both necessary and sufficient to drive NB4 cells through an intermediate cell fate decision point to initiate terminal granulopoiesis. Moreover, ectopic expression of SPI1 and CEBPE promoted granulocytic differentiation in non-APL leukemia cell lines HL60 and K562. Our study sheds mechanistic insights into the differentiation trajectories induced by ATRA and illustrates a gene regulatory circuit that could be widely applied to promote differentiation of leukemia cells.

Cis-regulatory chromatin contacts form de novo in the absence of loop extrusion

NIPBL promotes chromatin loop extrusion by the cohesin complex until it stalls at convergently oriented CTCF sites, leading to the formation of structural loops. However, to what extent loop extrusion contributes to the establishment vs maintenance of cis-regulatory element (CRE) connectivity is poorly understood. Here, we explored the de novo establishment of chromatin folding patterns at the mitosis-to-G1-phase transition upon acute NIPBL loss. NIPBL depletion primarily impaired the formation of cohesion-mediated structural loops with NIPBL dependence being proportional to loop length. In contrast, the majority of CRE loops were established independently of loop extrusion regardless of length. However, NIPBL depletion slowed the re-formation of CRE loops with weak enhancers. Transcription of genes at NIPBL-independent loop anchors was activated normally in the absence of NIPBL. In sum, establishment of most regulatory contacts and gene transcription following mitotic exit is independent of loop extrusion.

Establishment of the REMBAC-cassette, a rapid, efficient and manifold BacMam tool for recombinant protein expression

Efficient recombinant protein production requires mammalian stable cell lines or often relies on inefficient transfection processes. Baculoviral transduction of mammalian cells (BacMam) offers cost-effective and robust gene transfer and straightforward scalability. The advantages over conventional approaches are, no need of high biosafety level laboratories, efficient transduction of various cell types and transfer of large transgenes into host cells. In our study, we aim to develop a high expression cassette to increase yields of baculoviral transduction. The establishment follows a sequential approach by first identifying the strongest promoter, followed by intron and WPRE sequences as enhancer elements for transcription and translation. The resulting REMBAC-cassette was compared to conventional transfection in suspension and adherent cells. Irrespective of the cell line, transduction reached nearly 100 % efficiency and led to almost 10-fold increases of gene expression levels. We confirmed these results in larger scale with batch and fed-batch cultivations. Finally, expression of different soluble proteins with high degrees of complexity confirmed the versatility of our established cassette. Overall, the REMBAC-cassette incorporated into the BacMam platform is a manifold tool offering advantages over standard transfection, in the scalability, efficiency and gene expression, which results in higher yields, shorter cultivation times and consequently cost-effective production processes.

Inhibition of triglyceride metabolism-associated enhancers alters lipid deposition during adipocyte differentiation

Triglyceride (TG) metabolism is a complex and highly coordinated biological process regulated by a series of genes, and its dysregulation can lead to the occurrence of disorders in lipid metabolism. However, the transcriptional regulatory mechanisms of crucial genes in TG metabolism mediated by enhancer-promoter interactions remain elusive. Here, we identified candidate enhancers regulating the Agpat2, Dgat1, Dgat2, Pnpla2, and Lipe genes in 3T3-L1 adipocytes by integrating epigenomic data (H3K27ac, H3K4me1, and DHS-seq) with chromatin three-dimensional interaction data. Luciferase reporter assays revealed that 11 enhancers exhibited fluorescence activity. The repression of enhancers using the dCas9-KRAB system revealed the functional roles of enhancers of Dgat2 and Pnpla2 in regulating their expression and TG metabolism. Furthermore, transcriptome analyses revealed that inhibition of Dgat2-En4 downregulated pathways associated with lipid metabolism, lipid biosynthesis, and adipocyte differentiation. Additionally, overexpression and motif mutation experiments of transcription factor found that two TFs, PPARG and RXRA, regulate the activity of Agpat2-En1, Dgat2-En4, and Pnpla2-En5. Our study identified functional enhancers regulating TG metabolism and elucidated potential regulatory mechanisms of TG deposition from enhancer-promoter interactions, providing insights into understanding lipid deposition.

LDB1 establishes multi-enhancer networks to regulate gene expression

How specific enhancer-promoter pairing is established remains mostly unclear. Besides the CTCF/cohesin machinery, few nuclear factors have been studied for a direct role in physically connecting regulatory elements. Using a murine erythroid cell model, we show via acute degradation experiments that LDB1 directly and broadly promotes connectivity among regulatory elements. Most LDB1-mediated contacts, even those spanning hundreds of kb, can form in the absence of CTCF, cohesin, or YY1 as determined using multiple degron systems. Moreover, an engineered LDB1-driven chromatin loop is cohesin independent. Cohesin-driven loop extrusion does not stall at LDB1-occupied sites but aids the formation of a subset of LDB1-anchored loops. Leveraging the dynamic reorganization of nuclear architecture during the transition from mitosis to G1 phase, we observe that loop formation and de novo LDB1 occupancy correlate and can occur independently of structural loops. Tri-C and Region Capture Micro-C reveal that LDB1 organizes multi-enhancer networks to activate transcription. These findings establish LDB1 as a driver of spatial connectivity.

Two coacting shadow enhancers regulate twin of eyeless expression during early Drosophila development

The Drosophila PAX6 homolog twin of eyeless (toy) sits at the pinnacle of the genetic pathway controlling eye development, the retinal determination network. Expression of toy in the embryo is first detectable at cellular blastoderm stage 5 in an anterior-dorsal band in the presumptive procephalic neuroectoderm, which gives rise to the primordia of the visual system and brain. Although several maternal and gap transcription factors that generate positional information in the embryo have been implicated in controlling toy, the regulation of toy expression in the early embryo is currently not well characterized. In this study, we adopt an integrated experimental approach utilizing bioinformatics, molecular genetic testing of putative enhancers in transgenic reporter gene assays and quantitative analysis of expression patterns in the early embryo, to identify 2 novel coacting enhancers at the toy gene. In addition, we apply mathematical modeling to dissect the regulatory landscape for toy. We demonstrate that relatively simple thermodynamic-based models, incorporating only 5 TF binding sites, can accurately predict gene expression from the 2 coacting enhancers and that the HUNCHBACK TF plays a critical regulatory role through a dual-modality function as an activator and repressor. Our analysis also reveals that the molecular architecture of the 2 enhancers is very different, indicating that the underlying regulatory logic they employ is distinct.

An enhancer-promoter-transcription factor module orchestrates plant immune homeostasis by constraining camalexin biosynthesis

Effective plant defense against pathogens relies on highly coordinated regulation of immune gene expression. Enhancers, as cis-regulatory elements, are indispensable determinants of dynamic gene regulation, but the molecular functions in plant immunity are not well understood. In this study, we identified a novel enhancer, CORE PATTERN-INDUCED ENHANCER 35 (CPIE35), which is rapidly activated upon pathogenic elicitation and negatively regulates antifungal resistance through modulating WRKY15 expression. During immune activation, CPIE35 activates the transcription of WRKY15 by forming chromatin loops with the promoter of WRKY15 in a WRKY18/40/60-, WRKY33-, and MYC2-dependent manner. WRKY15 directly binds to the promoters of PAD3 and GSTU4, suppressing their expression and leading to reduced camalexin synthesis and resistance. Interestingly, CPIE35 region is evolutionarily conserved among Brassicaceae plants, and the CPIE35-WRKY15 module exerts similar functions in Brassica napus to negatively regulate antifungal resistance. Our work reveals the "enhancer-promoter-transcription factor" regulatory mechanism in maintenance of immune homeostasis, highlighting the importance and conserved role of enhancers in fine-tuning immune gene expression in plants.

Transcription factor clusters as information transfer agents

Deciphering how genes interpret information from transcription factor (TF) concentrations within the cell nucleus remains a fundamental question in gene regulation. Recent advancements have revealed the heterogeneous distribution of TF molecules, posing challenges to precisely decoding concentration signals. Using high-resolution single-cell imaging of the fluorescently tagged TF Bicoid in living Drosophila embryos, we show that Bicoid accumulation in submicrometer clusters preserves the spatial information of the maternal Bicoid gradient. These clusters provide precise spatial cues through intensity, size, and frequency. We further discover that Bicoid target genes colocalize with these clusters in an enhancer-binding affinity-dependent manner. Our modeling suggests that clustering offers a faster sensing mechanism for global nuclear concentrations than freely diffusing TF molecules detected by simple enhancers.

Epigenetic basis for the establishment of ruminal tissue-specific functions in bovine fetuses and adults

Epigenetic regulation in the rumen, a unique ruminant organ, remains largely unexplored compared with other tissues studied in model species. In this study, we perform an in-depth analysis of the epigenetic and transcriptional landscapes across fetal and adult bovine tissues as well as pluripotent stem cells. Among the extensive methylation differences across various stages and tissues, we identify tissue-specific differentially methylated regions (tsDMRs) unique to the rumen, which are crucial for regulating epithelial development and energy metabolism. These tsDMRs cluster within super-enhancer regions that overlap with transcription factor (TF) binding sites. Regression models indicate that DNA methylation, along with H3K27me3 and H3K27ac, can be used to predict enhancer activity. Key upstream TFs, including SOX2, FOSL1/2, and SMAD2/3, primarily maintain an inhibitory state through bivalent modifications during fetal development. Downstream functional genes are maintained mainly in a stable repressive state via DNA methylation until differentiation is complete. Our study underscores the critical role of tsDMRs in regulating distal components of rumen morphology and function, providing key insights into the epigenetic regulatory mechanisms that may influence bovine production traits.

Predicting genome-wide tissue-specific enhancers via combinatorial transcription factor genomic occupancy analysis

Enhancers are non-coding cis-regulatory elements crucial for transcriptional regulation. Mutations in enhancers can disrupt gene regulation, leading to disease phenotypes. Identifying enhancers and their tissue-specific activity is challenging due to their lack of stereotyped sequences. This study presents a sequence-based computational model that uses combinatorial transcription factor (TF) genomic occupancy to predict tissue-specific enhancers. Trained on diverse datasets, including ENCODE and Vista enhancer browser data, the model predicted 25 000 forebrain-specific cis-regulatory modules (CRMs) in the human genome. Validation using biochemical features, disease-associated SNPs, and in vivo zebrafish analysis confirmed its effectiveness. This model aids in predicting enhancers lacking well-characterized chromatin features, complementing experimental approaches in tissue-specific enhancer discovery.

Central control of dynamic gene circuits governs T cell rest and activation

The ability of cells to maintain distinct identities and respond to transient environmental signals requires tightly controlled regulation of gene networks1-3. These dynamic regulatory circuits that respond to extracellular cues in primary human cells remain poorly defined. The need for context-dependent regulation is prominent in T cells, where distinct lineages must respond to diverse signals to mount effective immune responses and maintain homeostasis4-8. Here we performed CRISPR screens in multiple primary human CD4+ T cell contexts to identify regulators that control expression of IL-2Rα, a canonical marker of T cell activation transiently expressed by pro-inflammatory effector T cells and constitutively expressed by anti-inflammatory regulatory T cells where it is required for fitness9-11. Approximately 90% of identified regulators of IL-2Rα had effects that varied across cell types and/or stimulation states, including a subset that even had opposite effects across conditions. Using single-cell transcriptomics after pooled perturbation of context-specific screen hits, we characterized specific factors as regulators of overall rest or activation and constructed state-specific regulatory networks. MED12 - a component of the Mediator complex - serves as a dynamic orchestrator of key regulators, controlling expression of distinct sets of regulators in different T cell contexts. Immunoprecipitation-mass spectrometry revealed that MED12 interacts with the histone methylating COMPASS complex. MED12 was required for histone methylation and expression of genes encoding key context-specific regulators, including the rest maintenance factor KLF2 and the versatile regulator MYC. CRISPR ablation of MED12 blunted the cell-state transitions between rest and activation and protected from activation-induced cell death. Overall, this work leverages CRISPR screens performed across conditions to define dynamic gene circuits required to establish resting and activated T cell states.

A genome-wide scan of non-coding RNAs and enhancers for refractive error and myopia

Refractive error (RE) and myopia are complex polygenic conditions with the majority of genome-wide associated genetic variants in non-exonic regions. Given this, and the onset during childhood, gene-regulation is expected to play an important role in its pathogenesis. This prompted us to explore beyond traditional gene finding approaches. We performed a genetic association study between variants in non-coding RNAs and enhancers, and RE and myopia. We obtained single-nucleotide polymorphisms (SNPs) in microRNA (miRNA) genes, miRNA-binding sites, long non-coding RNAs genes (lncRNAs) and enhancers from publicly available databases: miRNASNPv2, PolymiRTS, VISTA Enhancer Browser, FANTOM5 and lncRNASNP2. We investigated whether SNPs overlapping these elements were associated with RE and myopia leveraged from a large GWAS meta-analysis (N = 160,420). With genetic risk scores (GRSs) per element, we investigated the joint effect of associated variants on RE, axial length (AL)/corneal radius (CR), and AL progression in an independent child cohort, the Generation R Study (N = 3638 children). We constructed a score for biological plausibility per SNP in highly confident miRNA-binding sites and enhancers in chromatin accessible regions. We found that SNPs in two miRNA genes, 14 enhancers and 81 lncRNA genes in chromatin accessible regions and 54 highly confident miRNA-binding sites, were in RE and myopia-associated loci. GRSs from SNPs in enhancers were significantly associated with RE, AL/CR and AL progression. GRSs from lncRNAs were significantly associated with all AL/CR and AL progression. GRSs from miRNAs were not associated with any ocular biometric measurement. GRSs from miRNA-binding sites showed suggestive but inconsistent significance. We prioritized candidate miRNA binding sites and candidate enhancers for future functional validation. Pathways of target and host genes of highly ranked variants included eye development (BMP4, MPPED2), neurogenesis (DDIT4, NTM), extracellular matrix (ANTXR2, BMP3), photoreceptor metabolism (DNAJB12), photoreceptor morphogenesis (CHDR1), neural signaling (VIPR2) and TGF-beta signaling (ANAPC16). This is the first large-scale study of non-coding RNAs and enhancers for RE and myopia. Enhancers and lncRNAs could be of large importance as they are associated with childhood myopia. We provide a confident blueprint for future functional validation by prioritizing candidate miRNA binding sites and candidate enhancers.

Promoter Analysis and Dissection Using Reporter Genes, Comparative Genomics, and Gel Shift Assays in Phytophthora

Transcriptional regulation allows cells to execute developmental programs, maintain homeostasis, and respond to intra- and extracellular signals. Central to these processes are promoters, which in eukaryotes are sequences upstream of genes that bind transcription factors (TFs) and which recruit RNA polymerase to initiate mRNA synthesis. Valuable tools for studying promoters include reporter genes, which can be used to indicate when and where genes are activated. Moreover, functional regions within promoters (typically TF binding sites) can be identified by integrating reporter assays with promoter mutagenesis. These sites may also be revealed through comparative genomics, or by the DNA-protein binding procedure known as a gel shift or electrophoretic mobility shift assay (EMSA). The latter can also be used to test if a specific TF binds a DNA target or assess the binding kinetics or affinity of the complex. In this chapter, we describe procedures for expressing reporter genes in Phytophthora, assaying reporter activity, identifying functional sites within promoters, and testing purified TFs or proteins within nuclear extracts for DNA binding.

HDI-STARR-seq: Condition-specific enhancer discovery in mouse liver in vivo

BACKGROUND

STARR-seq and other massively-parallel reporter assays are widely used to discover functional enhancers in transfected cell models, which can be confounded by plasmid vector-induced type-I interferon immune responses and lack the multicellular environment and endogenous chromatin state of complex mammalian tissues.

RESULTS

We describe HDI-STARR-seq, which combines STARR-seq plasmid library delivery to the liver, by hydrodynamic tail vein injection (HDI), with reporter RNA transcriptional initiation driven by a minimal Albumin promoter, which we show is essential for mouse liver STARR-seq enhancer activity assayed 7 days after HDI. Importantly, little or no vector-induced innate type-I interferon responses were observed. Comparisons of HDI-STARR-seq activity between male and female mouse livers and in livers from males treated with an activating ligand of the transcription factor (TF) CAR (Nr1i3) identified many condition-dependent enhancers linked to condition-specific gene expression. Further, thousands of active liver enhancers were identified using a high complexity STARR-seq library comprised of ~ 50,000 genomic regions released by DNase-I digestion of mouse liver nuclei. When compared to stringently inactive library sequences, the active enhancer sequences identified were highly enriched for liver open chromatin regions with activating histone marks (H3K27ac, H3K4me1, H3K4me3), were significantly closer to gene transcriptional start sites, and were significantly depleted of repressive (H3K27me3, H3K9me3) and transcribed region histone marks (H3K36me3).

CONCLUSION

HDI-STARR-seq offers substantial improvements over current methodologies for large scale, functional profiling of enhancers, including condition-dependent enhancers, in liver tissue in vivo, and can be adapted to characterize enhancer activities in a variety of species and tissues by selecting suitable tissue- and species-specific promoter sequences.

Single chromatin fiber profiling and nucleosome position mapping in the human brain

We apply a single-molecule chromatin fiber sequencing (Fiber-seq) protocol designed for amplification-free cell-type-specific mapping of the regulatory architecture at nucleosome resolution along extended ∼10-kb chromatin fibers to neuronal and non-neuronal nuclei sorted from human brain tissue. Specifically, application of this method enables the resolution of cell-selective promoter and enhancer architectures on single fibers, including transcription factor footprinting and position mapping, with sequence-specific fixation of nucleosome arrays flanking transcription start sites and regulatory motifs. We uncover haplotype-specific chromatin patterns, multiple regulatory elements cis-aligned on individual fibers, and accessible chromatin at 20,000 unique sites encompassing retrotransposons and other repeat sequences hitherto "unmappable" by short-read epigenomic sequencing. Overall, we show that Fiber-seq is applicable to human brain tissue, offering sharp demarcation of nucleosome-depleted regions at sites of open chromatin in conjunction with multi-kilobase nucleosomal positioning at single-fiber resolution on a genome-wide scale.

Advancing microbiota therapeutics: the role of synthetic biology in engineering microbial communities for precision medicine

Over recent years, studies on microbiota research and synthetic biology have explored novel approaches microbial manipulation for therapeutic purposes. However, fragmented information is available on this aspect with key insights scattered across various disciplines such as molecular biology, genetics, bioengineering, and medicine. This review aims to the transformative potential of synthetic biology in advancing microbiome research and therapies, with significant implications for healthcare, agriculture, and environmental sustainability. By merging computer science, engineering, and biology, synthetic biology allows for precise design and modification of biological systems via cutting edge technologies like CRISPR/Cas9 gene editing, metabolic engineering, and synthetic oligonucleotide synthesis, thus paving the way for targeted treatments such as personalized probiotics and engineered microorganisms. The review will also highlight the vital role of gut microbiota in disorders caused by its dysbiosis and suggesting microbiota-based therapies and innovations such as biosensors for real-time gut health monitoring, non-invasive diagnostic tools, and automated bio foundries for better outcomes. Moreover, challenges including genetic stability, environmental safety, and robust regulatory frameworks will be discussed to understand the importance of ongoing research to ensure safe and effective microbiome interventions.

DNA regulatory element cooperation and competition in transcription

Regulation of eukaryotic transcription is a complex process that enables precise temporal and spatial control of gene expression. Promoters, which are cis-regulatory elements (CREs) located proximal to the transcription start site (TSS), selectively integrate regulatory cues from distal CREs, or enhancers, and their associated transcriptional machinery. In this review, we discuss current knowledge regarding CRE cooperation and competition impacting gene expression, including features of enhancer-promoter, enhancer-enhancer, and promoter-promoter interplay. We also provide an overview of recent insights into the underlying molecular mechanisms that facilitate physical and functional interaction of regulatory elements, such as the involvement of enhancer RNAs and biomolecular condensates. [BMB Reports 2024; 57(12): 509-520].

Neurodevelopmental functions and activities of the KAT3 class of lysine acetyltransferases

The human lysine acetyltransferases KAT3A (CREBBP) and KAT3B (EP300) are essential enzymes in gene regulation in the nucleus. Their ubiquitous expression in metazoan cell types controls cell proliferation and differentiation during development. This comprehensive review delves into the biological roles of KAT3A and KAT3B in neurodevelopment, shedding light on how alterations in their regulation or activity can potentially contribute to a spectrum of neurodegenerative diseases (e.g., Huntington's and Alzheimer's). We explore the pathophysiological implications of KAT3 function loss in these disorders, considering their conserved protein domains and biochemical functions in chromatin regulation. The discussion also underscores the crucial role of KAT3 proteins and their substrates in supporting the integration of key cell signaling pathways. Furthermore, the narrative highlights the interdependence of KAT3-mediated lysine acetylation with lysine methylation and arginine methylation. From a cellular perspective, KAT3-dependent signal integration at subnuclear domains is mediated by liquid-liquid phase separation in response to KAT3-mediated lysine acetylation. The disruption of these finely tuned regulatory processes underscores their pathological roles in neurodegeneration. This review also points to the exciting potential for future research in this field, inspiring further investigation and discovery in the area of neurodevelopment and neurodegenerative diseases.

A novel interpretable deep learning-based computational framework designed synthetic enhancers with broad cross-species activity

Enhancers play a critical role in dynamically regulating spatial-temporal gene expression and establishing cell identity, underscoring the significance of designing them with specific properties for applications in biosynthetic engineering and gene therapy. Despite numerous high-throughput methods facilitating genome-wide enhancer identification, deciphering the sequence determinants of their activity remains challenging. Here, we present the DREAM (DNA cis-Regulatory Elements with controllable Activity design platforM) framework, a novel deep learning-based approach for synthetic enhancer design. Proficient in uncovering subtle and intricate patterns within extensive enhancer screening data, DREAM achieves cutting-edge sequence-based enhancer activity prediction and highlights critical sequence features implicating strong enhancer activity. Leveraging DREAM, we have engineered enhancers that surpass the potency of the strongest enhancer within the Drosophila genome by approximately 3.6-fold. Remarkably, these synthetic enhancers exhibited conserved functionality across species that have diverged more than billion years, indicating that DREAM was able to learn highly conserved enhancer regulatory grammar. Additionally, we designed silencers and cell line-specific enhancers using DREAM, demonstrating its versatility. Overall, our study not only introduces an interpretable approach for enhancer design but also lays out a general framework applicable to the design of other types of cis-regulatory elements.

Entangled and non-modular enhancer sequences producing independent spatial activities

The modularity of transcriptional enhancers is central to our understanding of morphological evolution, allowing specific changes to a gene expression pattern component, without affecting others. Enhancer modularity refers to physically separated stretches of regulatory sequence producing discrete spatiotemporal transcriptional activity. This concept stems from assays that test the sufficiency of a DNA segment to drive spatial reporter expression resembling that of the corresponding gene. Focusing on spatial patterns, it overlooks quantitative aspects of gene expression, underestimating the regulatory sequence actually required to reach full endogenous expression levels. Here, we show that five regulatory activities of the gene yellow in Drosophila, classically described as modular, result from extensively overlapping sequences, with broadly distributed regulatory information. Nevertheless, the independent regulatory activities of these entangled enhancers appear to be nucleated by specific segments that we called enhancer cores. Our work calls for a reappraisal of enhancer definition and properties, as well as of the consequences on regulatory evolution.

Learning genotype-phenotype associations from gaps in multi-species sequence alignments

Understanding the genetic basis of phenotypic variation is fundamental to biology. Here we introduce GAP, a novel machine learning framework for predicting binary phenotypes from gaps in multi-species sequence alignments. GAP employs a neural network to predict the presence or absence of phenotypes solely from alignment gaps, contrasting with existing tools that require additional and often inaccessible input data. GAP can be applied to three distinct problems: predicting phenotypes in species from known associated genomic regions, pinpointing positions within such regions that are important for predicting phenotypes, and extracting sets of candidate regions associated with phenotypes. We showcase the utility of GAP by exploiting the well-known association between the L-gulonolactone oxidase (Gulo) gene and vitamin C synthesis, demonstrating its perfect prediction accuracy in 34 vertebrates. This exceptional performance also applies more generally, with GAP achieving high accuracy and power on a large simulated dataset. Moreover, predictions of vitamin C synthesis in species with unknown status mirror their phylogenetic relationships, and positions with high predictive importance are consistent with those identified by previous studies. Last, a genome-wide application of GAP identifies many additional genes that may be associated with vitamin C synthesis, and analysis of these candidates uncovers functional enrichment for immunity, a widely recognized role of vitamin C. Hence, GAP represents a simple yet useful tool for predicting genotype-phenotype associations and addressing diverse evolutionary questions from data available in a broad range of study systems.

A LANA peptide inhibits tumor growth by inducing CHD4 protein cleavage and triggers cell death

Kaposi's sarcoma-associated herpesvirus (KSHV) establishes a latent infection, and viral genes are poised to be transcribed in the latent chromatin. In the poised chromatins, KSHV latency-associated nuclear antigen (LANA) interacts with cellular chromodomain-helicase-DNA-binding protein 4 (CHD4) and inhibits viral promoter activation. CHD4 is known to regulate cell differentiation by preventing enhancers from activating promoters. Here, we identified a putative CHD4 inhibitor peptide (VGN73) from the LANA sequence corresponding to the LANA-CHD4 interaction surface. The VGN73 interacts with CHD4 at its PHD domain with a dissociation constant (KD) of 14 nM. Pre-treatment with VGN73 enhanced monocyte differentiation into macrophages and globally altered the repertoire of activated genes in U937 cells. Furthermore, the introduction of the peptide into the cancer cells induced caspase-mediated CHD4 cleavage, triggered cell death, and inhibited tumor growth in a xenograft mouse model. The VGN73 may facilitate cell differentiation therapy.

Characterization of the Cannabis sativa glandular trichome epigenome

BACKGROUND

The relationship between epigenomics and plant specialised metabolism remains largely unexplored despite the fundamental importance of epigenomics in gene regulation and, potentially, yield of products of plant specialised metabolic pathways. The glandular trichomes of Cannabis sativa are an emerging model system that produce large quantities of cannabinoid and terpenoid specialised metabolites with known medicinal and commercial value. To address this lack of epigenomic data, we mapped H3K4 trimethylation, H3K56 acetylation, H3K27 trimethylation post-translational modifications and the histone variant H2A.Z, using chromatin immunoprecipitation, in C. sativa glandular trichomes, leaf, and stem tissues. Corresponding transcriptomic (RNA-seq) datasets were integrated, and tissue-specific analyses conducted to relate chromatin states to glandular trichome specific gene expression.

RESULTS

The promoters of cannabinoid and terpenoid biosynthetic genes, specialised metabolite transporter genes, defence related genes, and starch and sucrose metabolism were enriched specifically in trichomes for histone marks H3K4me3 and H3K56ac, consistent with active transcription. We identified putative trichome-specific enhancer elements by identifying intergenic regions of H3K56ac enrichment, a histone mark that maintains enhancer accessibility, then associated these to putative target genes using the tissue specific gene transcriptomic data. Bi-valent chromatin loci specific to glandular trichomes, marked with H3K4 trimethylation and H3K27 trimethylation, were associated with genes of MAPK signalling pathways and plant specialised metabolism pathways, supporting recent hypotheses that implicate bi-valent chromatin in plant defence. The histone variant H2A.Z was largely found in intergenic regions and enriched in chromatin that contained genes involved in DNA homeostasis.

CONCLUSION

We report the first genome-wide histone post-translational modification maps for C. sativa glandular trichomes, and more broadly for glandular trichomes in plants. Our findings have implications in plant adaptation and stress responses and provide a basis for enhancer-mediated, targeted, gene transformation studies in plant glandular trichomes.

Transcription factor clusters as information transfer agents

Deciphering how genes interpret information from the concentration of transcription factors (TFs) within the cell nucleus remains a fundamental question in gene regulation. Recent advancements have unveiled the heterogeneous distribution of TF molecules in the nucleus, posing challenges to the precise decoding of concentration signals. To explore this phenomenon, we employ high-resolution single-cell imaging of a fluorescently tagged TF protein, Bicoid, in living fly embryos. We show that accumulation of Bicoid in submicron clusters preserves the spatial information of the maternal Bicoid gradient, and that cluster intensity, size, and frequency offer remarkably precise spatial cues. We further discover that various known gene targets of Bicoid activation colocalize with clusters and that for the target gene Hunchback, this colocalization is dependent on its enhancer binding affinity. Modeling information transfer through these clusters suggests that clustering offers a more rapid sensing mechanism for global nuclear concentrations than freely diffusing TF molecules detected by simple enhancers.

DeepDualEnhancer: A Dual-Feature Input DNABert Based Deep Learning Method for Enhancer Recognition

Enhancers are cis-regulatory DNA sequences that are widely distributed throughout the genome. They can precisely regulate the expression of target genes. Since the features of enhancer segments are difficult to detect, we propose DeepDualEnhancer, a DNABert-based method using a multi-scale convolutional neural network, BiLSTM, for enhancer identification. We first designed the DeepDualEnhancer method based only on the DNA sequence input. It mainly consists of a multi-scale Convolutional Neural Network, and BiLSTM to extract features by DNABert and embedding, respectively. Meanwhile, we collected new datasets from the enhancer-promoter interaction field and designed the method DeepDualEnhancer-genomic for inputting DNA sequences and genomic signals, which consists of the transformer sequence attention. Extensive comparisons of our method with 20 other excellent methods through 5-fold cross validation, ablation experiments, and an independent test demonstrated that DeepDualEnhancer achieves the best performance. It is also found that the inclusion of genomic signals helps the enhancer recognition task to be performed better.

Repeated Shifts in Sociality Are Associated With Fine-tuning of Highly Conserved and Lineage-Specific Enhancers in a Socially Flexible Bee

Comparative genomic studies of social insects suggest that changes in gene regulation are associated with evolutionary transitions in social behavior, but the activity of predicted regulatory regions has not been tested empirically. We used self-transcribing active regulatory region sequencing, a high-throughput enhancer discovery tool, to identify and measure the activity of enhancers in the socially variable sweat bee, Lasioglossum albipes. We identified over 36,000 enhancers in the L. albipes genome from 3 social and 3 solitary populations. Many enhancers were identified in only a subset of L. albipes populations, revealing rapid divergence in regulatory regions within this species. Population-specific enhancers were often proximal to the same genes across populations, suggesting compensatory gains and losses of regulatory regions may preserve gene activity. We also identified 1,182 enhancers with significant differences in activity between social and solitary populations, some of which are conserved regulatory regions across species of bees. These results indicate that social trait variation in L. albipes is associated with the fine-tuning of ancient enhancers as well as lineage-specific regulatory changes. Combining enhancer activity with population genetic data revealed variants associated with differences in enhancer activity and identified a subset of differential enhancers with signatures of selection associated with social behavior. Together, these results provide the first empirical map of enhancers in a socially flexible bee and highlight links between cis-regulatory variation and the evolution of social behavior.

CRISPR tiling deletion screens reveal functional enhancers of neuropsychiatric risk genes and allelic compensation effects (ACE) on transcription

Precise transcriptional regulation is critical for cellular function and development, yet the mechanism of this process remains poorly understood for many genes. To gain a deeper understanding of the regulation of neuropsychiatric disease risk genes, we identified a total of 39 functional enhancers for four dosage-sensitive genes, APP, FMR1, MECP2, and SIN3A, using CRISPR tiling deletion screening in human induced pluripotent stem cell (iPSC)-induced excitatory neurons. We found that enhancer annotation provides potential pathological insights into disease-associated copy number variants. More importantly, we discovered that allelic enhancer deletions at SIN3A could be compensated by increased transcriptional activities from the other intact allele. Such allelic compensation effects (ACE) on transcription is stably maintained during differentiation and, once established, cannot be reversed by ectopic SIN3A expression. Further, ACE at SIN3A occurs through dosage sensing by the promoter. Together, our findings unravel a regulatory compensation mechanism that ensures stable and precise transcriptional output for SIN3A, and potentially other dosage-sensitive genes.

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.

FAS gene expression, prognostic significance and molecular interactions in lung cancer

Introduction

FAS has been implicated in the development of various cancers, but its involvement in lung cancer has not been systematically characterized. In this study, we performed data mining in online tumor databases to investigate the expression, methylation, alterations, protein interactions, co-expression and prognostic significance of FAS in lung cancer.

Method

The expression, prognostic significance and molecular interactions of FAS in lung cancer was mined and analyzed using GENT2, GEPIA2, UALCAN, cBioPortal, STRING, GeneMANIA, UCSC Xena, Enrichr, and OSluca databases. FAS expression was subsequently investigated at the protein level in samples from 578 lung cancer patients to understand its protein-level expression. In vitro validation of FAS gene expression was performed on H1299, H1993, A549 and HBE cell lines.

Result

We found that the expression of FAS was significantly downregulated in both lung adenocarcinoma (LUAD) and lung squamous cell carcinoma (LUSC) compared to normal lung tissue. In addition, we observed a higher level of FAS promoter methylation in LUSC tissue than in normal tissue. FAS alterations were rare (1.9%) in lung cancer samples, with deep deletions being more common than missense mutations, which occurred mainly in the TNFR-like cysteine-rich domain and the death domain. We also identified a list of proteins interacting with FAS and genes co-expressed with FAS, with LUAD having 11 co-expressed genes and LUSC having 90 co-expressed genes. Our results also showed that FAS expression has limited prognostic significance (HR=1.302, 95% CI=0.935-1.139, P=0.530). Protein level investigation revealed that FAS expression varied among individuals, with nTPM values ranging from 5.2 to 67.2.

Conclusion

This study provides valuable insights into the involvements and characteristics of FAS in lung cancer. Further studies are needed to investigate the clinical significance of FAS alterations in lung cancer and to explore the potential of targeting FAS for therapeutic intervention.

EnhancerNet: a predictive model of cell identity dynamics through enhancer selection

Understanding how cell identity is encoded by the genome and acquired during differentiation is a central challenge in cell biology. I have developed a theoretical framework called EnhancerNet, which models the regulation of cell identity through the lens of transcription factor-enhancer interactions. I demonstrate that autoregulation in these interactions imposes a constraint on the model, resulting in simplified dynamics that can be parameterized from observed cell identities. Despite its simplicity, EnhancerNet recapitulates a broad range of experimental observations on cell identity dynamics, including enhancer selection, cell fate induction, hierarchical differentiation through multipotent progenitor states and direct reprogramming by transcription factor overexpression. The model makes specific quantitative predictions, reproducing known reprogramming recipes and the complex haematopoietic differentiation hierarchy without fitting unobserved parameters. EnhancerNet provides insights into how new cell types could evolve and highlights the functional importance of distal regulatory elements with dynamic chromatin in multicellular evolution.

Multiple promoter and enhancer differences likely contribute to augmented G6PC2 expression in human versus mouse pancreatic islet alpha cells

G6PC2 encodes a glucose-6-phosphatase catalytic subunit that opposes the action of glucokinase in pancreatic islets, thereby modulating the sensitivity of insulin and glucagon secretion to glucose. In mice, G6pc2 is expressed at ~20-fold higher levels in β-cells than in α-cells, whereas in humans G6PC2 is expressed at only ~5-fold higher levels in β-cells. We therefore hypothesize that G6PC2 likely influences glucagon secretion to a greater degree in humans. With a view to generating a humanized mouse that recapitulates augmented G6PC2 expression levels in α-cells, we sought to identify the genomic regions that confer differential mouse G6pc2 expression in α-cells versus β-cells as well as the evolutionary changes that have altered this ratio in humans. Studies in islet-derived cell lines suggest that the elevated G6pc2 expression in mouse β-cells versus α-cells is mainly due to a difference in the relative activity of the proximal G6pc2 promoter in these cell types. Similarly, the smaller difference in G6PC2 expression between α-cells and β-cells in humans is potentially explained by a change in relative proximal G6PC2 promoter activity. However, we show that both glucocorticoid levels and multiple differences in the relative activity of eight transcriptional enhancers between mice and humans likely contribute to differential G6PC2 expression. Finally, we show that a mouse-specific non-coding RNA, Gm13613, whose expression is controlled by G6pc2 enhancer I, does not regulate G6pc2 expression, indicating that altered expression of Gm13613 in a humanized mouse that contains both the human promoter and enhancers should not affect G6PC2 function.

Nucleosome placement and polymer mechanics explain genomic contacts on 100kbp scales

The 3d organization of the genome - in particular, which two regions of DNA are in contact with each other - plays a role in regulating gene expression. Several factors influence genome 3d organization. Nucleosomes (where ~ 100 basepairs of DNA wrap around histone proteins) also bend, twist and compactify chromosomal DNA, altering its polymer mechanics. How much does the positioning of nucleosomes between gene loci influence contacts between those gene loci? And, to what extent is polymer mechanics responsible for this? To address this question, we combine a stochastic polymer mechanics model of chromosomal DNA including twists and wrapping induced by nucleosomes with two data-driven pipelines. The first estimates nucleosome positioning from ATACseq data in regions of high accessibility. Most of the genome is low-accessibility, so we combine this with a novel image analysis method that estimates the distribution of nucleosome spacing from electron microscopy data. There are no free parameters in the biophysical model. We apply this method to IL6, IL15, CXCL9, and CXCL10, inflammatory marker genes in macrophages, before and after immune stimulation, and compare the predictions with contacts measured by conformation capture experiments (4C-seq). We find that within a 500 kilo-basepairs genomic region, polymer mechanics with nucleosomes can explain 71% of close contacts. These results suggest that, while genome contacts on 100kbp-scales are multifactorial, they may be amenable to mechanistic, physical explanation. Our work also highlights the role of nucleosomes, not just at the loci of interest, but between them, and not just the total number of nucleosomes, but their specific placement. The method generalizes to other genes, and can be used to address whether a contact is under active regulation by the cell (e.g., a macrophage during inflammatory stimulation). Importantly, our findings suggest that gene function may have evolved through selective pressures that co-opted contact-mediated regulatory mechanisms reliant largely on polymer mechanics.

Three-dimensional chromatin mapping of sensory neurons reveals that promoter-enhancer looping is required for axonal regeneration

The in vivo three-dimensional genomic architecture of adult mature neurons at homeostasis and after medically relevant perturbations such as axonal injury remains elusive. Here, we address this knowledge gap by mapping the three-dimensional chromatin architecture and gene expression program at homeostasis and after sciatic nerve injury in wild-type and cohesin-deficient mouse sensory dorsal root ganglia neurons via combinatorial Hi-C, promoter-capture Hi-C, CUT&Tag for H3K27ac and RNA-seq. We find that genes involved in axonal regeneration form long-range, complex chromatin loops, and that cohesin is required for the full induction of the regenerative transcriptional program. Importantly, loss of cohesin results in disruption of chromatin architecture and severely impaired nerve regeneration. Complex enhancer-promoter loops are also enriched in the human fetal cortical plate, where the axonal growth potential is highest, and are lost in mature adult neurons. Together, these data provide an original three-dimensional chromatin map of adult sensory neurons in vivo and demonstrate a role for cohesin-dependent long-range promoter interactions in nerve regeneration.

Transcriptional silencing in Saccharomyces cerevisiae: known unknowns

Transcriptional silencing in Saccharomyces cerevisiae is a persistent and highly stable form of gene repression. It involves DNA silencers and repressor proteins that bind nucleosomes. The silenced state is influenced by numerous factors including the concentration of repressors, nature of activators, architecture of regulatory elements, modifying enzymes and the dynamics of chromatin.Silencers function to increase the residence time of repressor Sir proteins at silenced domains while clustering of silenced domains enables increased concentrations of repressors and helps facilitate long-range interactions. The presence of an accessible NDR at the regulatory regions of silenced genes, the cycling of chromatin configurations at regulatory sites, the mobility of Sir proteins, and the non-uniform distribution of the Sir proteins across the silenced domain, all result in silenced chromatin that only stably silences weak promoters and enhancers via changes in transcription burst duration and frequency.These data collectively suggest that silencing is probabilistic and the robustness of silencing is achieved through sub-optimization of many different nodes of action such that a stable expression state is generated and maintained even though individual constituents are in constant flux.

Intrinsic Epigenetic State of Primary Osteosarcoma Drives Metastasis

Osteosarcoma is the most common primary malignant bone tumor affecting the pediatric population with a high potential to metastasize. However, insights into the molecular features enabling its metastatic potential are limited. We mapped the active chromatin landscapes of osteosarcoma tumors by integrating histone H3 lysine-acetylated chromatin state (n = 13), chromatin accessibility profiles (n = 11), and gene expression (n = 13) to understand the differences in their active chromatin profiles and their impact on molecular mechanisms driving the malignant phenotypes. Primary osteosarcoma tumors from patients with metastasis (primary met) have a distinct active chromatin landscape compared with those without metastasis (localized). This difference shapes the transcriptional profile of osteosarcoma. We identified novel candidate genes, including PPP1R1B, PREX1, and IGF2BP1, that exhibit increased chromatin activity in primary met. Loss of PREX1 in primary met osteosarcoma cells significantly diminishes osteosarcoma proliferation, invasion, migration, and colony formation capacity. Differential chromatin activity in primary met is associated with genes regulating cytoskeleton organization, cellular adhesion, and extracellular matrix, suggesting their role in facilitating osteosarcoma metastasis. Chromatin profiling of tumors from metastatic lung lesions shows increased chromatin activity in genes involved in cell migration and Wnt pathway. These data demonstrate that metastatic potential is intrinsically present in primary met tumors, with cellular chromatin profiles further adapting for successful dissemination, migration, and colonization at the distal site. Implications: Our study demonstrates that metastatic potential is intrinsic to primary metastatic osteosarcoma tumors, with chromatin profiles further adapting for successful dissemination, migration, and colonization at the distal metastatic site.

An integrated transcription factor framework for Treg identity and diversity

Vertebrate cell identity depends on the combined activity of scores of transcription factors (TF). While TFs have often been studied in isolation, a systematic perspective on their integration has been missing. Focusing on FoxP3+ regulatory T cells (Tregs), key guardians of immune tolerance, we combined single-cell chromatin accessibility, machine learning, and high-density genetic variation, to resolve a validated framework of diverse Treg chromatin programs, each shaped by multi-TF inputs. This framework identified previously unrecognized Treg controllers (Smarcc1) and illuminated the mechanism of action of FoxP3, which amplified a pre-existing Treg identity, diversely activating or repressing distinct programs, dependent on different regulatory partners. Treg subpopulations in the colon relied variably on FoxP3, Helios+ Tregs being completely dependent, but RORγ+ Tregs largely independent. These differences were rooted in intrinsic biases decoded by the integrated framework. Moving beyond master regulators, this work unravels how overlapping TF activities coalesce into Treg identity and diversity.

Genome binding properties of Zic transcription factors underlie their changing functions during neuronal maturation

BACKGROUND

The Zic family of transcription factors (TFs) promote both proliferation and maturation of cerebellar granule neurons (CGNs), raising the question of how a single, constitutively expressed TF family can support distinct developmental processes. Here we use an integrative experimental and bioinformatic approach to discover the regulatory relationship between Zic TF binding and changing programs of gene transcription during postnatal CGN differentiation.

RESULTS

We first established a bioinformatic pipeline to integrate Zic ChIP-seq data from the developing mouse cerebellum with other genomic datasets from the same tissue. In newborn CGNs, Zic TF binding predominates at active enhancers that are co-bound by developmentally regulated TFs including Atoh1, whereas in mature CGNs, Zic TF binding consolidates toward promoters where it co-localizes with activity-regulated TFs. We then performed CUT&RUN-seq in differentiating CGNs to define both the time course of developmental shifts in Zic TF binding and their relationship to gene expression. Mapping Zic TF binding sites to genes using chromatin looping, we identified the set of Zic target genes that have altered expression in RNA-seq from Zic1 or Zic2 knockdown CGNs.

CONCLUSIONS

Our data show that Zic TFs are required for both induction and repression of distinct, developmentally regulated target genes through a mechanism that is largely independent of changes in Zic TF binding. We suggest that the differential collaboration of Zic TFs with other TF families underlies the shift in their biological functions across CGN development.

Efficient and multiplex gene upregulation in plants through CRISPR-Cas-mediated knockin of enhancers

Gene upregulation through genome editing is important for plant research and breeding. Targeted insertion of short transcriptional enhancers (STEs) into gene promoters may offer a universal solution akin to transgene-mediated overexpression while avoiding the drawbacks associated with transgenesis. Here, we introduce an "in locus activation" technique in rice that leverages well-characterized STEs for refined, heritable, and multiplexed gene upregulation. To address the scarcity of potent enhancers, we developed a large-scale mining approach and discovered a suite of STEs that are capable of enhancing gene expression in rice protoplasts. The in locus integration of these STEs into eight rice genes resulted in substantial transcriptional upregulation in the edited plants, with up to 869.1-fold increases in their transcript levels. Employing a variety of STEs, we achieved delicate control of gene expression, enabling the fine-tuning of key phenotypic traits such as plant height. Our approach also enabled efficient multiplexed gene upregulation, with up to four genes activated simultaneously, significantly enhancing the nicotinamide mononucleotide metabolic pathway. Importantly, heritability studies from the T0 to T3 generations confirmed the stable and heritable nature of STE-driven gene activation. Collectively, our work demonstrates that coupled with STE mining, leveraging genome editing for in locus activation and gene upregulation holds great promise to be widely adopted in fundamental plant research and crop breeding.

Enhlink infers distal and context-specific enhancer-promoter linkages

Enhlink is a computational tool for scATAC-seq data analysis, facilitating precise interrogation of enhancer function at the single-cell level. It employs an ensemble approach incorporating technical and biological covariates to infer condition-specific regulatory DNA linkages. Enhlink can integrate multi-omic data for enhanced specificity, when available. Evaluation with simulated and real data, including multi-omic datasets from the mouse striatum and novel promoter capture Hi-C data, demonstrate that Enhlink outperfoms alternative methods. Coupled with eQTL analysis, it identified a putative super-enhancer in striatal neurons. Overall, Enhlink offers accuracy, power, and potential for revealing novel biological insights in gene regulation.