The chromatin Remodeler CHD8 is required for activation of progesterone receptor-dependent enhancers

Neurodevelopmental functions of CHD8: new insights and questions

Heterozygous, de novo, loss-of-function variants of the CHD8 gene are associated with a high penetrance of autism and other neurodevelopmental phenotypes. Identifying the neurodevelopmental functions of high-confidence autism risk genes like CHD8 may improve our understanding of the neurodevelopmental mechanisms that underlie autism spectrum disorders. Over the last decade, a complex picture of pleiotropic CHD8 functions and mechanisms of action has emerged. Multiple brain and non-brain cell types and progenitors appear to be affected by CHD8 haploinsufficiency. Behavioural, cellular and synaptic phenotypes are dependent on the nature of the gene mutation and are modified by sex and genetic background. Here, I review some of the CHD8-interacting proteins and molecular mechanisms identified to date, as well as the impacts of CHD8 deficiency on cellular processes relevant to neurodevelopment. I endeavour to highlight some of the critical questions that still require careful and concerted attention over the next decade to bring us closer to the goal of understanding the salient mechanisms whereby CHD8 deficiency causes neurodevelopmental disorders.

The EstroGene Database Reveals Diverse Temporal, Context-Dependent, and Bidirectional Estrogen Receptor Regulomes in Breast Cancer

As one of the most successful cancer therapeutic targets, estrogen receptor-α (ER/ESR1) has been extensively studied over the past few decades. Sequencing technological advances have enabled genome-wide analysis of ER action. However, comparison of individual studies is limited by different experimental designs, and few meta-analyses are available. Here, we established the EstroGene database through unified processing of data from 246 experiments including 136 transcriptomic, cistromic, and epigenetic datasets focusing on estradiol (E2)-triggered ER activation across 19 breast cancer cell lines. A user-friendly browser (https://estrogene.org/) was generated for multiomic data visualization involving gene inquiry under user-defined experimental conditions and statistical thresholds. Notably, annotation of metadata associated with public datasets revealed a considerable lack of experimental details. Comparison of independent RNA-seq or ER ChIP-seq data with the same design showed large variability and only strong effects could be consistently detected. Temporal estrogen response metasignatures were defined, and the association of E2 response rate with temporal transcriptional factors, chromatin accessibility, and heterogeneity of ER expression was evaluated. Unexpectedly, harmonizing 146 E2-induced transcriptomic datasets uncovered a subset of genes harboring bidirectional E2 regulation, which was linked to unique transcriptional factors and highly associated with immune surveillance in the clinical setting. Furthermore, the context dependent E2 response programs were characterized in MCF7 and T47D cell lines, the two most frequently used models in the EstroGene database. Collectively, the EstroGene database provides an informative and practical resource to the cancer research community to uniformly evaluate key reproducible features of ER regulomes and unravels modes of ER signaling.

SIGNIFICANCE

A resource database integrating 246 publicly available ER profiling datasets facilitates meta-analyses and identifies estrogen response temporal signatures, a bidirectional program, and model-specific biases.

EstroGene database reveals diverse temporal, context-dependent and directional estrogen receptor regulomes in breast cancer

As one of the most successful cancer therapeutic targets, estrogen receptor-α (ER/ESR1) has been extensively studied in decade-long. Sequencing technological advances have enabled genome-wide analysis of ER action. However, reproducibility is limited by different experimental design. Here, we established the EstroGene database through centralizing 246 experiments from 136 transcriptomic, cistromic and epigenetic datasets focusing on estradiol-treated ER activation across 19 breast cancer cell lines. We generated a user-friendly browser ( https://estrogene.org/ ) for data visualization and gene inquiry under user-defined experimental conditions and statistical thresholds. Notably, documentation-based meta-analysis revealed a considerable lack of experimental details. Comparison of independent RNA-seq or ER ChIP-seq data with the same design showed large variability and only strong effects could be consistently detected. We defined temporal estrogen response metasignatures and showed the association with specific transcriptional factors, chromatin accessibility and ER heterogeneity. Unexpectedly, harmonizing 146 transcriptomic analyses uncovered a subset of E2-bidirectionally regulated genes, which linked to immune surveillance in the clinical setting. Furthermore, we defined context dependent E2 response programs in MCF7 and T47D cell lines, the two most frequently used models in the field. Collectively, the EstroGene database provides an informative resource to the cancer research community and reveals a diverse mode of ER signaling.

The autism risk factor CHD8 is a chromatin activator in human neurons and functionally dependent on the ERK-MAPK pathway effector ELK1

The chromodomain helicase DNA-binding protein CHD8 is the most frequently mutated gene in autism spectrum disorder. Despite its prominent disease involvement, little is known about its molecular function in the human brain. CHD8 is a chromatin regulator which binds to the promoters of actively transcribed genes through genomic targeting mechanisms which have yet to be fully defined. By generating a conditional loss-of-function and an endogenously tagged allele in human pluripotent stem cells, we investigated the molecular function and the interaction of CHD8 with chromatin in human neurons. Chromatin accessibility analysis and transcriptional profiling revealed that CHD8 functions as a transcriptional activator at its target genes in human neurons. Furthermore, we found that CHD8 chromatin targeting is cell context-dependent. In human neurons, CHD8 preferentially binds at ETS motif-enriched promoters. This enrichment is particularly prominent on the promoters of genes whose expression significantly changes upon the loss of CHD8. Indeed, among the ETS transcription factors, we identified ELK1 as being most highly correlated with CHD8 expression in primary human fetal and adult cortical neurons and most highly expressed in our stem cell-derived neurons. Remarkably, ELK1 was necessary to recruit CHD8 specifically to ETS motif-containing sites. These findings imply that ELK1 and CHD8 functionally cooperate to regulate gene expression and chromatin states at MAPK/ERK target genes in human neurons. Our results suggest that the MAPK/ERK/ELK1 axis potentially contributes to the pathogenesis caused by CHD8 mutations in human neurodevelopmental disorders.

Single-cell multiomics reveals the complexity of TGFβ signalling to chromatin in iPSC-derived kidney organoids

TGFβ1 plays a regulatory role in the determination of renal cell fate and the progression of renal fibrosis. Here we show an association between SMAD3 and the histone methyltransferase, EZH2, during cell differentiation; ChIP-seq revealed that SMAD3 and EZH2 co-occupy the genome in iPSCs and in iPSC-derived nephron progenitors. Through integration of single cell gene expression and epigenome profiling, we identified de novo ACTA2^+ve/POSTN^+ve myofibroblasts in kidney organoids treated with TGFβ1, characterised by increased SMAD3-dependent cis chromatin accessibility and gene expression associated with fibroblast activation. We have identified fibrosis-associated regulons characterised by enrichment of SMAD3, AP1, the ETS family of transcription factors, and NUAK1, CREB3L1, and RARG, corresponding to enriched motifs at accessible loci identified by scATACseq. Treatment with the EZH2 specific inhibitor GSK343, blocked SMAD3-dependent cis co-accessibility and inhibited myofibroblast activation. This mechanism, through which TGFβ signals directly to chromatin, represents a critical determinant of fibrotic, differentiated states.

In vivo targeted DamID identifies CHD8 genomic targets in fetal mouse brain

Genetic studies of autism have revealed causal roles for chromatin remodeling gene mutations. Chromodomain helicase DNA binding protein 8 (CHD8) encodes a chromatin remodeler with significant de novo mutation rates in sporadic autism. However, relationships between CHD8 genomic function and autism-relevant biology remain poorly elucidated. Published studies utilizing ChIP-seq to map CHD8 protein-DNA interactions have high variability, consistent with technical challenges and limitations associated with this method. Thus, complementary approaches are needed to establish CHD8 genomic targets and regulatory functions in developing brain. We used in utero CHD8 Targeted DamID followed by sequencing (TaDa-seq) to characterize CHD8 binding in embryonic mouse cortex. CHD8 TaDa-seq reproduced interaction patterns observed from ChIP-seq and further highlighted CHD8 distal interactions associated with neuronal loci. This study establishes TaDa-seq as a useful alternative for mapping protein-DNA interactions in vivo and provides insights into the regulatory targets of CHD8 and autism-relevant pathophysiology associated with CHD8 mutations.

Sentinels of chromatin: chromodomain helicase DNA-binding proteins in development and disease

Chromatin is highly dynamic, undergoing continuous global changes in its structure and type of histone and DNA modifications governed by processes such as transcription, repair, replication, and recombination. Members of the chromodomain helicase DNA-binding (CHD) family of enzymes are ATP-dependent chromatin remodelers that are intimately involved in the regulation of chromatin dynamics, altering nucleosomal structure and DNA accessibility. Genetic studies in yeast, fruit flies, zebrafish, and mice underscore essential roles of CHD enzymes in regulating cellular fate and identity, as well as proper embryonic development. With the advent of next-generation sequencing, evidence is emerging that these enzymes are subjected to frequent DNA copy number alterations or mutations and show aberrant expression in malignancies and other human diseases. As such, they might prove to be valuable biomarkers or targets for therapeutic intervention.

CHD8 safeguards early neuroectoderm differentiation in human ESCs and protects from apoptosis during neurogenesis

The chromatin remodeler CHD8, which belongs to the ATP-dependent chromatin remodelers CHD family, is one of the most high-risk mutated genes in autism spectrum disorders. However, the role of CHD8 in neural differentiation and the mechanism of CHD8 in autism remains unclear, despite there are a few studies based on the CHD8 haploinsufficient models. Here, we generate the CHD8 knockout human ESCs by CRISPR/Cas9 technology and characterize the effect of loss-of-function of CHD8 on pluripotency maintenance and lineage determination by utilizing efficient directed differentiation protocols. The results show loss-of-function of CHD8 does not affect human ESC maintenance although having slight effect on proliferation and cell cycle. Interestingly, CHD8 depletion results in defective neuroectoderm differentiation, along with severe cell death in neural progenitor stage. Transcriptome analysis also indicates CHD8 does not alter the expression of pluripotent genes in ESC stage, but in neural progenitor cells depletion of CHD8 induces the abnormal expression of the apoptosis genes and suppresses neuroectoderm-related genes. These results provide the evidence that CHD8 plays an essential role in the pluripotency exit and neuroectoderm differentiation as well as the regulation of apoptosis during neurogenesis.

FOXA1: A Pioneer of Nuclear Receptor Action in Breast Cancer

The pioneering function of FOXA1 establishes estrogen-responsive transcriptomes in luminal breast cancer. Dysregulated FOXA1 chromatin occupancy through focal amplification, mutation, or cofactor recruitment modulates estrogen receptor (ER) transcriptional programs and drives endocrine-resistant disease. However, ER is not the sole nuclear receptor (NR) expressed in breast cancers, nor is it the only NR for which FOXA1 serves as a licensing factor. Receptors for androgens, glucocorticoids, and progesterone are also found in the majority of breast cancers, and their functions are also impacted by FOXA1. These NRs interface with ER transcriptional programs and, depending on their activation level, can reprogram FOXA1-ER cistromes. Thus, NR interplay contributes to endocrine therapy response and resistance and may provide a vulnerability for future therapeutic benefit in patients. Herein, we review what is known regarding FOXA1 regulation of NR function in breast cancer in the context of cell identity, endocrine resistance, and NR crosstalk in breast cancer progression and treatment.

Expression analysis of progesterone‑regulated miRNAs in cells derived from human glioblastoma

Glioblastomas (GBMs) are the most frequent and malignant type of brain tumor. It has been reported that progesterone (P4) regulates the progression of GBMs by modifying the expression of genes that promote cell proliferation, migration and invasion; however, it is not fully understood how these processes are regulated. It is possible that P4 mediates some of these effects through changes in the microRNA (miRNA) expression profile in GBM cells. The present study investigated the effects of P4 on miRNAs expression profile in U-251MG cells derived from a human GBM. U-251MG cells were treated for 6 h with P4, RU486 (an antagonist of the intracellular progesterone receptor), the combined treatment (P4+RU486) and cyclodextrin (vehicle) and then a miRNA microarray analysis conducted. The expression analysis revealed a set of 190 miRNAs with differential expression in the treatments of P4, RU486 and P4+RU486 in respect to the vehicle and P4 in respect to P4+RU486, of which only 16 were exclusively regulated by P4. The possible mRNA targets of the miRNAs regulated by P4 could participate in the regulation of proliferation, cell cycle progression and cell migration of GBMs. The present study provided insight for understanding epigenetic modifications regulated by sex hormones involved in GBM progression, and for identifying potential therapeutic strategies for these brain tumors.

Chd8 regulates X chromosome inactivation in mouse through fine-tuning control of Xist expression

Female mammals achieve dosage compensation by inactivating one of their two X chromosomes during development, a process entirely dependent on Xist, an X-linked long non-coding RNA (lncRNA). At the onset of X chromosome inactivation (XCI), Xist is up-regulated and spreads along the future inactive X chromosome. Contextually, it recruits repressive histone and DNA modifiers that transcriptionally silence the X chromosome. Xist regulation is tightly coupled to differentiation and its expression is under the control of both pluripotency and epigenetic factors. Recent evidence has suggested that chromatin remodelers accumulate at the X Inactivation Center (XIC) and here we demonstrate a new role for Chd8 in Xist regulation in differentiating ES cells, linked to its control and prevention of spurious transcription factor interactions occurring within Xist regulatory regions. Our findings have a broader relevance, in the context of complex, developmentally-regulated gene expression.

Chromatin Remodeler CHD8 in Autism and Brain Development

Chromodomain Helicase DNA-binding 8 (CHD8) is a high confidence risk factor for autism spectrum disorders (ASDs) and the genetic cause of a distinct neurodevelopmental syndrome with the core symptoms of autism, macrocephaly, and facial dysmorphism. The role of CHD8 is well-characterized at the structural, biochemical, and transcriptional level. By contrast, much less is understood regarding how mutations in CHD8 underpin altered brain function and mental disease. Studies on various model organisms have been proven critical to tackle this challenge. Here, we scrutinize recent advances in this field with a focus on phenotypes in transgenic animal models and highlight key findings on neurodevelopment, neuronal connectivity, neurotransmission, synaptic and homeostatic plasticity, and habituation. Against this backdrop, we further discuss how to improve future animal studies, both in terms of technical issues and with respect to the sex-specific effects of Chd8 mutations for neuronal and higher-systems level function. We also consider outstanding questions in the field including 'humanized' mice models, therapeutic interventions, and how the use of pluripotent stem cell-derived cerebral organoids might help to address differences in neurodevelopment trajectories between model organisms and humans.

High glucose-ROS conditions enhance the progression in cholangiocarcinoma via upregulation of MAN2A2 and CHD8

Diabetes is a major risk factor in the development and progression of several cancers including cholangiocarcinoma (CCA). However, the molecular mechanism by which hyperglycemia potentiates progression of CCA is not clearly understood. Here, we showed that a high glucose condition significantly increased reactive oxygen species (ROS) production and promoted aggressive phenotypes of CCA cells, including proliferation and migration activities. Mannosidase alpha class 2a member 2 (MAN2A2), was upregulated at both mRNA and protein levels in a high glucose‐ and ROS‐dependent manner. In addition, cell proliferation and migration were significantly reduced by MAN2A2 knockdown. Based on our proteome and in silico analyses, we further found that chromodomain helicase DNA‐binding protein 8 (CHD8) was induced by ROS signaling and regulated MAN2A2 expression. Overexpression of CHD8 increased MAN2A2 expression, while CHD8 knockdown dramatically reduced proliferation and migration as well as MAN2A2 expression in CCA cells. Moreover, both MAN2A2 and CHD8 were highly expressed with positive correlation in CCA tumor tissues. Collectively, these data suggested that high glucose conditions promote CCA progression through ROS‐mediated upregulation of MAN2A2 and CHD8. Thus, glucose metabolism is a promising therapeutic target to control tumor progression in patients with CCA and diabetes.

Chd8 Rescued TBI-Induced Neurological Deficits by Suppressing Apoptosis and Autophagy Via Wnt Signaling Pathway

Traumatic brain injury (TBI) and autism spectrum disorder (ASDs) share several same biochemical mechanisms and symptoms, such as learning memory impairments and communication deficits. Chromodomain helicase DNA binding protein 8 (CHD8), a member of the CHD family of ATP-dependent chromatin remodeling factors, is one of the top risk genetic factors in ASDs and is highly associated with Wnt/β-catenin signaling. Yet, the possible effect of CHD8 on TBI remains poorly understood. In vivo, we found that Chd8 co-localized in neurons, astrocytes, and microglia, but predominantly presented in neurons in the prefrontal cortex, hippocampus, and cortex. Both Chd8 and β-catenin expression peaked at 12 h and shared the similar change tendency after TBI. Chd8 knockdown inhibited wnt pathway, promoted the activation of apoptosis and autophagy, and caused learning and memory impairments both at normal and TBI condition. In addition, overexpression of Chd8 via 17β-estrogen (E2) treatment enhanced wnt signaling pathway and suppressed TBI-induced apoptosis and autophagic activation. In vitro, a significant increase of Chd8 and β-catenin expression was observed in HT22 cells after lipopolysaccharide (lps) treatment or mechanical injury, respectively. Chd8 knockdown inhibited wnt signaling pathway and increased apoptosis and autophagy activation in lps-stimulated HT22 cells. But activation of wnt signaling inverted the effects of Chd8-siRNA. Our results demonstrated that Chd8 exerted neuroprotection and promoted cognitive recovery through inhibiting apoptosis and autophagy activation following TBI, at least partially by wnt signaling pathway.

Tissue-specific progesterone receptor-chromatin binding and the regulation of progesterone-dependent gene expression

Progesterone receptor (PGR) co-ordinately regulates ovulation, fertilisation and embryo implantation through tissue-specific actions, but the mechanisms for divergent PGR action are poorly understood. Here we characterised PGR activity in mouse granulosa cells using combined ChIP-seq for PGR and H3K27ac and gene expression microarray. Comparison of granulosa, uterus and oviduct PGR-dependent genes showed almost complete tissue specificity in PGR target gene profiles. In granulosa cells 82% of identified PGR-regulated genes bound PGR within 3 kb of the gene and PGR binding sites were highly enriched in proximal promoter regions in close proximity to H3K27ac-modified active chromatin. Motif analysis showed highly enriched PGR binding to the PGR response element (GnACAnnnTGTnC), but PGR also interacted significantly with other transcription factor binding motifs. In uterus PGR showed far more tendency to bind intergenic chromatin regions and low evidence of interaction with other transcription factors. This is the first genome-wide description of PGR action in granulosa cells and systematic comparison of diverse PGR action in different reproductive tissues. It clarifies finely-tuned contextual PGR-chromatin interactions with implications for more targeted reproductive medicine.

Lineage specific transcription factors and epigenetic regulators mediate TGFβ-dependent enhancer activation

During neurogenesis, dynamic developmental cues, transcription factors and histone modifying enzymes regulate the gene expression programs by modulating the activity of neural-specific enhancers. How transient developmental signals coordinate transcription factor recruitment to enhancers and to which extent chromatin modifiers contribute to enhancer activity is starting to be uncovered. Here, we take advantage of neural stem cells as a model to unravel the mechanisms underlying neural enhancer activation in response to the TGFβ signaling. Genome-wide experiments demonstrate that the proneural factor ASCL1 assists SMAD3 in the binding to a subset of enhancers. Once located at the enhancers, SMAD3 recruits the histone demethylase JMJD3 and the remodeling factor CHD8, creating the appropriate chromatin landscape to allow enhancer transcription and posterior gene activation. Finally, to analyze the phenotypical traits owed to cis-regulatory regions, we use CRISPR–Cas9 technology to demonstrate that the TGFβ-responsive Neurog2 enhancer is essential for proper neuronal polarization.

Enhancers: bridging the gap between gene control and human disease

Enhancers are a class of regulatory elements essential for precise spatio-temporal control of gene expression during development and in terminally differentiated cells. This review highlights signature features of enhancer elements as well as new advances that provide mechanistic insights into enhancer-mediated gene control in the context of three-dimensional chromatin. We detail the various ways in which non-coding mutations can instigate aberrant gene control and cause a variety of Mendelian disorders, common diseases and cancer.

TBL1 is required for the mesenchymal phenotype of transformed breast cancer cells

The epithelial-to-mesenchymal transition (EMT) and its reversion (MET) are related to tumor cell dissemination and migration, tumor circulating cell generation, cancer stem cells, chemoresistance, and metastasis formation. To identify chromatin and epigenetic factors possibly involved in the process of EMT, we compare the levels of expression of epigenetic genes in a transformed human breast epithelial cell line (HMEC-RAS) versus a stable clone of the same cell line expressing the EMT master regulator ZEB1 (HMEC-RAS-ZEB1). One of the factors strongly induced in the HMEC-RAS-ZEB1 cells was Transducin beta-like 1 (TBL1), a component of the NCoR complex, which has both corepressor and coactivator activities. We show that TBL1 interacts with ZEB1 and that both factors cooperate to repress the promoter of the epithelial gene E-cadherin (CDH1) and to autoactivate the ZEB1 promoter. Consistent with its central role, TBL1 is required for mesenchymal phenotypes of transformed breast epithelial and breast cancer cell lines of the claudin-low subtype. Importantly, a high expression of the TBL1 gene correlates with poor prognosis and increased proportion of metastasis in breast cancer patients, indicating that the level of TBL1 expression can be used as a prognostic marker.

Common CHD8 Genomic Targets Contrast With Model-Specific Transcriptional Impacts of CHD8 Haploinsufficiency

The packaging of DNA into chromatin determines the transcriptional potential of cells and is central to eukaryotic gene regulation. Case sequencing studies have revealed mutations to proteins that regulate chromatin state, known as chromatin remodeling factors, with causal roles in neurodevelopmental disorders. Chromodomain helicase DNA binding protein 8 (CHD8) encodes a chromatin remodeling factor with among the highest de novo loss-of-function mutation rates in patients with autism spectrum disorder (ASD). However, mechanisms associated with CHD8 pathology have yet to be elucidated. We analyzed published transcriptomic data across CHD8 in vitro and in vivo knockdown and knockout models and CHD8 binding across published ChIP-seq datasets to identify convergent mechanisms of gene regulation by CHD8. Differentially expressed genes (DEGs) across models varied, but overlap was observed between downregulated genes involved in neuronal development and function, cell cycle, chromatin dynamics, and RNA processing, and between upregulated genes involved in metabolism and immune response. Considering the variability in transcriptional changes and the cells and tissues represented across ChIP-seq analysis, we found a surprisingly consistent set of high-affinity CHD8 genomic interactions. CHD8 was enriched near promoters of genes involved in basic cell functions and gene regulation. Overlap between high-affinity CHD8 targets and DEGs shows that reduced dosage of CHD8 directly relates to decreased expression of cell cycle, chromatin organization, and RNA processing genes, but only in a subset of studies. This meta-analysis verifies CHD8 as a master regulator of gene expression and reveals a consistent set of high-affinity CHD8 targets across human, mouse, and rat in vivo and in vitro studies. These conserved regulatory targets include many genes that are also implicated in ASD. Our findings suggest a model where perturbation to dosage-sensitive CHD8 genomic interactions with a highly-conserved set of regulatory targets leads to model-specific downstream transcriptional impacts.

Chromatin reprogramming in breast cancer

Reprogramming of the chromatin landscape is a critical component to the transcriptional response in breast cancer. Effects of sex hormones such as estrogens and progesterone have been well described to have a critical impact on breast cancer proliferation. However, the complex network of the chromatin landscape, enhancer regions and mode of function of steroid receptors (SRs) and other transcription factors (TFs), is an intricate web of signaling and functional processes that is still largely misunderstood at the mechanistic level. In this review, we describe what is currently known about the dynamic interplay between TFs with chromatin and the reprogramming of enhancer elements. Emphasis has been placed on characterizing the different modes of action of TFs in regulating enhancer activity, specifically, how different SRs target enhancer regions to reprogram chromatin in breast cancer cells. In addition, we discuss current techniques employed to study enhancer function at a genome-wide level. Further, we have noted recent advances in live cell imaging technology. These single-cell approaches enable the coupling of population-based assays with real-time studies to address many unsolved questions about SRs and chromatin dynamics in breast cancer.

Genome-wide identification of novel intergenic enhancer-like elements: implications in the regulation of transcription in Plasmodium falciparum

Background

The molecular mechanisms of transcriptional regulation are poorly understood in Plasmodium falciparum. In addition, most of the genes in Plasmodium falciparum are transcriptionally poised and only a handful of cis-regulatory elements are known to operate in transcriptional regulation. Here, we employed an epigenetic signature based approach to identify significance of previously uncharacterised intergenic regions enriched with histone modification marks leading to discovery of enhancer-like elements.

Results

We found that enhancer-like elements are significantly enriched with H3K4me1, generate unique non-coding bi-directional RNAs and majority of them can function as cis-regulators. Furthermore, functional enhancer reporter assay demonstrates that the enhancer-like elements regulate transcription of target genes in Plasmodium falciparum. Our study also suggests that the Plasmodium genome segregates functionally related genes into discrete housekeeping and pathogenicity/virulence clusters, presumably for robust transcriptional control of virulence/pathogenicity genes.

Conclusions

This report contributes to the understanding of parasite regulatory genomics by identification of enhancer-like elements, defining their epigenetic and transcriptional features and provides a resource of functional cis-regulatory elements that may give insights into the virulence/pathogenicity of Plasmodium falciparum.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-017-4052-4) contains supplementary material, which is available to authorized users.

The ATP-dependent chromatin remodeling enzymes CHD6, CHD7, and CHD8 exhibit distinct nucleosome binding and remodeling activities

Proper chromatin regulation is central to genome function and maintenance. The group III chromodomain–helicase–DNA-binding (CHD) family of ATP-dependent chromatin remodeling enzymes, comprising CHD6, CHD7, CHD8, and CHD9, has well-documented roles in transcription regulation, impacting both organism development and disease etiology. These four enzymes are similar in their constituent domains, but they fill surprisingly non-redundant roles in the cell, with deficiencies in individual enzymes leading to dissimilar disease states such as CHARGE syndrome or autism spectrum disorders. The mechanisms explaining their divergent, non-overlapping functions are unclear. In this study, we performed an in-depth biochemical analysis of purified CHD6, CHD7, and CHD8 and discovered distinct differences in chromatin remodeling specificities and activities among them. We report that CHD6 and CHD7 both bind with high affinity to short linker DNA, whereas CHD8 requires longer DNA for binding. As a result, CHD8 slides nucleosomes into positions with more flanking linker DNA than CHD7. Moreover, we found that, although CHD7 and CHD8 slide nucleosomes, CHD6 disrupts nucleosomes in a distinct non-sliding manner. The different activities of these enzymes likely lead to differences in chromatin structure and, thereby, transcriptional control, at the enhancer and promoter loci where these enzymes bind. Overall, our work provides a mechanistic basis for both the non-redundant roles and the diverse mutant disease states of these enzymes in vivo.

The pioneer factor OCT4 requires the chromatin remodeller BRG1 to support gene regulatory element function in mouse embryonic stem cells

Pioneer transcription factors recognise and bind their target sequences in inaccessible chromatin to establish new transcriptional networks throughout development and cellular reprogramming. During this process, pioneer factors establish an accessible chromatin state to facilitate additional transcription factor binding, yet it remains unclear how different pioneer factors achieve this. Here, we discover that the pluripotency-associated pioneer factor OCT4 binds chromatin to shape accessibility, transcription factor co-binding, and regulatory element function in mouse embryonic stem cells. Chromatin accessibility at OCT4-bound sites requires the chromatin remodeller BRG1, which is recruited to these sites by OCT4 to support additional transcription factor binding and expression of the pluripotency-associated transcriptome. Furthermore, the requirement for BRG1 in shaping OCT4 binding reflects how these target sites are used during cellular reprogramming and early mouse development. Together this reveals a distinct requirement for a chromatin remodeller in promoting the activity of the pioneer factor OCT4 and regulating the pluripotency network.

DOI:http://dx.doi.org/10.7554/eLife.22631.001

All cells in your body contain the same genetic information in the form of genes encoded within DNA. Yet, cells use this information in different ways so that the activities of individual genes within that DNA can vary from cell to cell. This allows identical cells to become different to each other and to adapt to changing circumstances.

A group of proteins called transcription factors control the activity of certain genes by binding to specific sites on DNA. However, this isn’t a straightforward process because DNA in human and other animal cells is usually associated with structures called nucleosomes that can block access to the DNA. Pioneer transcription factors, such as OCT4, are a specific group of transcription factors that can attach to DNA in spite of the nucleosomes, but it’s not clear how this is possible. Once pioneer transcription factors attach to DNA they can help other transcription factors to bind alongside them.

King et al. studied OCT4 in stem cells from mouse embryos to investigate how it is able to act as a pioneer transcription factor and control gene activity. The experiments show that several other transcription factors lose the ability to bind to DNA when OCT4 is absent. This leads to widespread changes in gene activity in the cells, which seems to be due to other transcription factors being unable to get past the nucleosomes to attach to the DNA.

Further experiments showed that OCT4 needs a protein called BRG1 in order to act as a pioneer transcription factor. BRG1 is an enzyme that is able to move and remove (remodel) nucleosomes attached to DNA, suggesting that normal transcription factor binding requires this activity. The next challenge is to investigate whether BRG1, or similar enzymes, are also needed by other pioneer transcription factors that are required for normal gene activity and cell identity. This will be important because many enzymes that remodel nucleosomes are disrupted in human diseases like cancer where cells lose their normal identity.

DOI:http://dx.doi.org/10.7554/eLife.22631.002

Enhancer deregulation in cancer and other diseases

Mutations in enhancer-associated chromatin-modifying components and genomic alterations in non-coding regions of the genome occur frequently in cancer, and other diseases pointing to the importance of enhancer fidelity to ensure proper tissue homeostasis. In this review, I will use specific examples to discuss how mutations in chromatin-modifying factors might affect enhancer activity of disease-relevant genes. I will then consider direct evidence from single nucleotide polymorphisms, small insertions, or deletions but also larger genomic rearrangements such as duplications, deletions, translocations, and inversions of specific enhancers to demonstrate how they have the ability to impact enhancer activity of disease genes including oncogenes and tumor suppressor genes. Considering that the scientific community only fairly recently has begun to focus its attention on "enhancer malfunction" in disease, I propose that multiple new enhancer-regulated and disease-relevant processes will be uncovered in the near future that will constitute the mechanistic basis for novel therapeutic avenues.

Enhancers as non-coding RNA transcription units: recent insights and future perspectives

Networks of regulatory enhancers dictate distinct cell identities and cellular responses to diverse signals by instructing precise spatiotemporal patterns of gene expression. However, 35 years after their discovery, enhancer functions and mechanisms remain incompletely understood. Intriguingly, recent evidence suggests that many, if not all, functional enhancers are themselves transcription units, generating non-coding enhancer RNAs. This observation provides a fundamental insight into the inter-regulation between enhancers and promoters, which can both act as transcription units; it also raises crucial questions regarding the potential biological roles of the enhancer transcription process and non-coding enhancer RNAs. Here, we review research progress in this field and discuss several important, unresolved questions regarding the roles and mechanisms of enhancers in gene regulation.

CRISPR/Cas9-mediated heterozygous knockout of the autism gene CHD8 and characterization of its transcriptional networks in neurodevelopment

Background

Disruptive mutation in the CHD8 gene is one of the top genetic risk factors in autism spectrum disorders (ASDs). Previous analyses of genome-wide CHD8 occupancy and reduced expression of CHD8 by shRNA knockdown in committed neural cells showed that CHD8 regulates multiple cell processes critical for neural functions, and its targets are enriched with ASD-associated genes.

Methods

To further understand the molecular links between CHD8 functions and ASD, we have applied the CRISPR/Cas9 technology to knockout one copy of CHD8 in induced pluripotent stem cells (iPSCs) to better mimic the loss-of-function status that would exist in the developing human embryo prior to neuronal differentiation. We then carried out transcriptomic and bioinformatic analyses of neural progenitors and neurons derived from the CHD8 mutant iPSCs.

Results

Transcriptome profiling revealed that CHD8 hemizygosity (CHD8^+/−) affected the expression of several thousands of genes in neural progenitors and early differentiating neurons. The differentially expressed genes were enriched for functions of neural development, β-catenin/Wnt signaling, extracellular matrix, and skeletal system development. They also exhibited significant overlap with genes previously associated with autism and schizophrenia, as well as the downstream transcriptional targets of multiple genes implicated in autism. Providing important insight into how CHD8 mutations might give rise to macrocephaly, we found that seven of the twelve genes associated with human brain volume or head size by genome-wide association studies (e.g., HGMA2) were dysregulated in CHD8^+/− neural progenitors or neurons.

Conclusions

We have established a renewable source of CHD8^+/− iPSC lines that would be valuable for investigating the molecular and cellular functions of CHD8. Transcriptomic profiling showed that CHD8 regulates multiple genes implicated in ASD pathogenesis and genes associated with brain volume.

Electronic supplementary material

The online version of this article (doi:10.1186/s13229-015-0048-6) contains supplementary material, which is available to authorized users.