CpG traffic lights are markers of regulatory regions in human genome

DNA methylation patterns of transcription factor binding regions characterize their functional and evolutionary contexts

BACKGROUND

DNA methylation is an important epigenetic modification which has numerous roles in modulating genome function. Its levels are spatially correlated across the genome, typically high in repressed regions but low in transcription factor (TF) binding sites and active regulatory regions. However, the mechanisms establishing genome-wide and TF binding site methylation patterns are still unclear.

RESULTS

Here we use a comparative approach to investigate the association of DNA methylation to TF binding evolution in mammals. Specifically, we experimentally profile DNA methylation and combine this with published occupancy profiles of five distinct TFs (CTCF, CEBPA, HNF4A, ONECUT1, FOXA1) in the liver of five mammalian species (human, macaque, mouse, rat, dog). TF binding sites are lowly methylated, but they often also have intermediate methylation levels. Furthermore, biding sites are influenced by the methylation status of CpGs in their wider binding regions even when CpGs are absent from the core binding motif. Employing a classification and clustering approach, we extract distinct and species-conserved patterns of DNA methylation levels at TF binding regions. CEBPA, HNF4A, ONECUT1, and FOXA1 share the same methylation patterns, while CTCF's differ. These patterns characterize alternative functions and chromatin landscapes of TF-bound regions. Leveraging our phylogenetic framework, we find DNA methylation gain upon evolutionary loss of TF occupancy, indicating coordinated evolution. Furthermore, each methylation pattern has its own evolutionary trajectory reflecting its genomic contexts.

CONCLUSIONS

Our epigenomic analyses indicate a role for DNA methylation in TF binding changes across species including that specific DNA methylation profiles characterize TF binding and are associated with their regulatory activity, chromatin contexts, and evolutionary trajectories.

Building Minimized Epigenetic Clock by iPlex MassARRAY Platform

Epigenetic clocks are valuable tools for estimating both chronological and biological age by assessing DNA methylation levels at specific CpG dinucleotides. While conventional epigenetic clocks rely on genome-wide methylation data, targeted approaches offer a more efficient alternative. In this study, we explored the feasibility of constructing a minimized epigenetic clock utilizing data acquired through the iPlex MassARRAY technology. The study enrolled a cohort of relatively healthy individuals, and their methylation levels of eight specific CpG dinucleotides in genes SLC12A5, LDB2, FIGN, ACSS3, FHL2, and EPHX3 were evaluated using the iPlex MassARRAY system and the Illumina EPIC array. The methylation level of five studied CpG sites demonstrated significant correlations with chronological age and an acceptable convergence of data obtained by the iPlex MassARRAY and Illumina EPIC array. At the same time, the methylation level of three CpG sites showed a weak relationship with age and exhibited a low concordance between the data obtained from the two technologies. The construction of the epigenetic clock involved the utilization of different machine-learning models, including linear models, deep neural networks (DNN), and gradient-boosted decision trees (GBDT). The results obtained from these models were compared with each other and with the outcomes generated by other well-established epigenetic clocks. In our study, the TabNet architecture (deep tabular data learning architecture) exhibited the best performance (best MAE = 5.99). Although our minimized epigenetic clock yielded slightly higher age prediction errors compared to other epigenetic clocks, it still represents a viable alternative to the genome-wide epigenotyping array.

Regulatory networks driving expression of genes critical for glioblastoma are controlled by the transcription factor c-Jun and the pre-existing epigenetic modifications

BACKGROUND

Glioblastoma (GBM, WHO grade IV) is an aggressive, primary brain tumor. Despite extensive tumor resection followed by radio- and chemotherapy, life expectancy of GBM patients did not improve over decades. Several studies reported transcription deregulation in GBMs, but regulatory mechanisms driving overexpression of GBM-specific genes remain largely unknown. Transcription in open chromatin regions is directed by transcription factors (TFs) that bind to specific motifs, recruit co-activators/repressors and the transcriptional machinery. Identification of GBM-related TFs-gene regulatory networks may reveal new and targetable mechanisms of gliomagenesis.

RESULTS

We predicted TFs-regulated networks in GBMs in silico and intersected them with putative TF binding sites identified in the accessible chromatin in human glioma cells and GBM patient samples. The Cancer Genome Atlas and Glioma Atlas datasets (DNA methylation, H3K27 acetylation, transcriptomic profiles) were explored to elucidate TFs-gene regulatory networks and effects of the epigenetic background. In contrast to the majority of tumors, c-Jun expression was higher in GBMs than in normal brain and c-Jun binding sites were found in multiple genes overexpressed in GBMs, including VIM, FOSL2 or UPP1. Binding of c-Jun to the VIM gene promoter was stronger in GBM-derived cells than in cells derived from benign glioma as evidenced by gel shift and supershift assays. Regulatory regions of the majority of c-Jun targets have distinct DNA methylation patterns in GBMs as compared to benign gliomas, suggesting the contribution of DNA methylation to the c-Jun-dependent gene expression.

CONCLUSIONS

GBM-specific TFs-gene networks identified in GBMs differ from regulatory pathways attributed to benign brain tumors and imply a decisive role of c-Jun in controlling genes that drive glioma growth and invasion as well as a modulatory role of DNA methylation.

CRISPR/Cas9 genome editing demonstrates functionality of the autoimmunity-associated SNP rs12946510

Genome-wide association studies (GWAS) map genetic associations of complex traits with precision limited to a linkage disequilibrium group. To translate GWAS results into new understanding of disease mechanisms, individual causative polymorphisms and their target genes should be identified. CRISPR/Cas9 genome editing can be used to create isogenic cell lines bearing alternative genotypes of candidate single-nucleotide polymorphisms to test their causality and to reveal gene targets. An intergenic polymorphism rs12946510 is associated with multiple sclerosis, inflammatory bowel disease and asthma. We created sublines of the T-helper cell line bearing alternative genotypes of rs12946510 and showed that its risk ("T") allele is associated with lower expression of IKZF3 and ORMDL3 genes and reduced cell activation. Our editing procedure can become an effective tool for discovering new genes involved in pathogenesis of complex diseases.

RUNX1/CEBPA Mutation in Acute Myeloid Leukemia Promotes Hypermethylation and Indicates for Demethylation Therapy

Acute myeloid leukemia (AML) is a rapidly progressing heterogeneous disease with a high mortality rate, which is characterized by hyperproliferation of atypical immature myeloid cells. The number of AML patients is expected to increase in the near future, due to the old-age-associated nature of AML and increased longevity in the human population. RUNX1 and CEBPA, key transcription factors (TFs) of hematopoiesis, are frequently and independently mutated in AML. RUNX1 and CEBPA can bind TET2 demethylase and attract it to their binding sites (TFBS) in cell lines, leading to DNA demethylation of the regions nearby. Since TET2 does not have a DNA-binding domain, TFs are crucial for its guidance to target genomic locations. In this paper, we show that RUNX1 and CEBPA mutations in AML patients affect the methylation of important regulatory sites that resulted in the silencing of several RUNX1 and CEBPA target genes, most likely in a TET2-dependent manner. We demonstrated that hypermethylation of TFBS in AML cells with RUNX1 mutations was associated with resistance to anticancer chemotherapy. Demethylation therapy restored expression of the RUNX1 target gene, BIK, and increased sensitivity of AML cells to chemotherapy. If our results are confirmed, mutations in RUNX1 could be an indication for prescribing the combination of cytotoxic and demethylation therapies.

MethReg: estimating the regulatory potential of DNA methylation in gene transcription

Epigenome-wide association studies often detect many differentially methylated sites, and many are located in distal regulatory regions. To further prioritize these significant sites, there is a critical need to better understand the functional impact of CpG methylation. Recent studies demonstrated that CpG methylation-dependent transcriptional regulation is a widespread phenomenon. Here, we present MethReg, an R/Bioconductor package that analyzes matched DNA methylation and gene expression data, along with external transcription factor (TF) binding information, to evaluate, prioritize and annotate CpG sites with high regulatory potential. At these CpG sites, TF-target gene associations are often only present in a subset of samples with high (or low) methylation levels, so they can be missed by analyses that use all samples. Using colorectal cancer and Alzheimer's disease datasets, we show MethReg significantly enhances our understanding of the regulatory roles of DNA methylation in complex diseases.

Strong parallel differential gene expression induced by hatchery rearing weakly associated with methylation signals in adult Coho Salmon (O. kisutch)

Human activities and resource exploitation led to a massive decline of wild salmonid populations, consequently, numerous conservation programs have been developed to supplement wild populations. However, many studies documented reduced fitness of hatchery-born relative to wild fish. Here, by using both RNA sequencing and Whole Genome Bisulfite Sequencing of hatchery and wild-born adult Coho salmon (Oncorhynchus kisutch) originating from two previously studied river systems, we show that early-life hatchery-rearing environment-induced significant and parallel gene expression differentiation is maintained until Coho come back to their natal river for reproduction. A total of 3,643 genes differentially expressed and 859 coexpressed genes were downregulated in parallel in hatchery-born fish from both rivers relative to their wild congeners. Among those genes, 26 displayed a significant relationship between gene expression and the median gene body methylation and 669 single CpGs displayed a significant correlation between methylation level and the associated gene expression. The link between methylation and gene expression was weak suggesting that DNA methylation is not the only player in mediating hatchery-related expression differences. Yet, significant gene expression differentiation was observed despite 18 months spent in a common environment (i.e., the sea). Finally, the differentiation is observed in parallel in two different river systems, highlighting the fact that early-life environment may account for at least some of the reduced fitness of the hatchery salmon in the wild. These results illustrate the relevance and importance of considering both epigenome and transcriptome to evaluate the costs and benefits of large-scale supplementation programs.

Functional characterization of the tomato HAIRPLUS gene reveals the implication of the epigenome in the control of glandular trichome formation

Trichomes are specialised epidermal cells developed in the aerial surface of almost every terrestrial plant. These structures form physical barriers, which combined with their capability of synthesis of complex molecules, prevent plagues from spreading and confer trichomes a key role in the defence against herbivores. In this work, the tomato gene HAIRPLUS (HAP) that controls glandular trichome density in tomato plants was characterised. HAP belongs to a group of proteins involved in histone tail modifications although some also bind methylated DNA. HAP loss of function promotes epigenomic modifications in the tomato genome reflected in numerous differentially methylated cytosines and causes transcriptomic changes in hap mutant plants. Taken together, these findings demonstrate that HAP links epigenome remodelling with multicellular glandular trichome development and reveal that HAP is a valuable genomic tool for pest resistance in tomato breeding.

Childhood adversity correlates with stable changes in DNA methylation trajectories in children and converges with epigenetic signatures of prenatal stress

Childhood maltreatment (CM) is an established major risk factor for a number of negative health outcomes later in life. While epigenetic mechanisms, such as DNA methylation (DNAm), have been proposed as a means of embedding this environmental risk factor, little is known about its timing and trajectory, especially in very young children. It is also not clear whether additional environmental adversities, often experienced by these children, converge on similar DNAm changes. Here, we calculated a cumulative adversity score, which additionally to CM includes socioeconomic status (SES), other life events, parental psychopathology and epigenetic biomarkers of prenatal smoking and alcohol consumption. We investigated the effects of CM alone as well as the adversity score on longitudinal DNAm trajectories in the Berlin Longitudinal Child Study. This is a cohort of 173 children aged 3-5 years at baseline of whom 86 were exposed to CM. These children were followed-up for 2 years with extensive psychometric and biological assessments as well as saliva collection at 5 time points providing genome-wide DNAm levels. Overall, only a few DNAm patterns were stable over this timeframe, but less than 10 DNAm regions showed significant changes. At baseline, neither CM nor the adversity score associated with DNAm changes. However, in 6 differentially methylated regions (DMRs), CM and the adversity score significantly moderated DNAm trajectories over time. A number of these DMRs have previously been associated with adverse prenatal exposures. In our study, children exposed to CM also presented with epigenetic signatures indicative of increased prenatal exposure to tobacco and alcohol, as compared to non-CM exposed children. These epigenetic signatures of prenatal exposure strongly correlate with DNAm regions associated with CM and the adversity score. Finally, weighted correlation network analysis revealed a module of CpGs exclusively associated with CM. While our study identifies DNAm loci specifically associated with CM, especially within long non-coding RNAs, the majority of associations were found with the adversity score with convergent association with indicators of adverse prenatal exposures. This study highlights the importance of mapping not only of the epigenome but also the exposome and extending the observational timeframe to well before birth.

Enhanced C/EBP binding to G·T mismatches facilitates fixation of CpG mutations in cancer and adult stem cells

Somatic mutations in regulatory sites of human stem cells affect cell identity or cause malignant transformation. By mining the human genome for co-occurrence of mutations and transcription factor binding sites, we show that C/EBP binding sites are strongly enriched with [C > T]G mutations in cancer and adult stem cells, which is of special interest because C/EBPs regulate cell fate and differentiation. In vitro protein-DNA binding assay and structural modeling of the CEBPB-DNA complex show that the G·T mismatch in the core CG dinucleotide strongly enhances affinity of the binding site. We conclude that enhanced binding of C/EBPs shields CpG·TpG mismatches from DNA repair, leading to selective accumulation of [C > T]G mutations and consequent deterioration of the binding sites. This mechanism of targeted mutagenesis highlights the effect of a mutational process on certain regulatory sites and reveals the molecular basis of putative regulatory alterations in stem cells.

Selective Nonmethylated CpG DNA Recognition Mechanism of Cysteine Clamp Domains

Methylation of DNA at CpG sites is a major mark for epigenetic regulation, but how transcription factors are influenced by CpG methylation is not well understood. Here, we report the molecular mechanisms of how the TCF (T-cell factor) and GEF (glucose transporter 4 enhancer factor) families of proteins selectively target unmethylated DNA sequences with a C-clamp type zinc finger domain. The structure of the C-clamp domain from human GEF family protein HDBP1 (C-clamp^HDBP1) in complex with DNA was determined using NMR spectroscopy, which adopts a unique zinc finger fold and selectively binds RCCGG (R = A/G) DNA sequences with an "Arg···Trp-Lys-Lys" DNA recognition motif inserted in the major groove. The CpG base pairs are central to the binding due to multiple hydrogen bonds formed with the backbone carbonyl groups of Trp378 and Lys379, as well as the side chain ε-amino groups of Lys379 and Lys380 from C-clamp^HDBP1. Consequently, methylation of the CpG dinucleotide almost abolishes the binding. Homology modeling reveals that the C-clamp domain from human TCF1E (C-clamp^TCF1E) binds DNA through essentially the same mechanism, with a similar "Arg···Arg-Lys-Lys" DNA recognition motif. The substitution of tryptophan by arginine makes C-clamp^HDBP1 prefer RCCGC DNA sequences. The two signature DNA recognition motifs are invariant in the GEF and TCF families of proteins, respectively, from fly to human. The recognition of the CpG dinucleotide through two consecutive backbone carbonyl groups is the same as that of the CXXC type unmethylated CpG DNA binding domains, suggesting a common mechanism shared by unmethylated CpG binding proteins.

Development of a prognostic risk model for clear cell renal cell carcinoma by systematic evaluation of DNA methylation markers

BACKGROUND

Current risk models for renal cell carcinoma (RCC) based on clinicopathological factors are sub-optimal in accurately identifying high-risk patients. Here, we perform a head-to-head comparison of previously published DNA methylation markers and propose a potential prognostic model for clear cell RCC (ccRCC).

PATIENTS AND METHODS

Promoter methylation of PCDH8, BNC1, SCUBE3, GREM1, LAD1, NEFH, RASSF1A, GATA5, SFRP1, CDO1, and NEURL was determined by nested methylation-specific PCR. To identify clinically relevant methylated regions, The Cancer Genome Atlas (TCGA) was used to guide primer design. Formalin-fixed paraffin-embedded (FFPE) tissue samples from 336 non-metastatic ccRCC patients from the prospective Netherlands Cohort Study (NLCS) were used to develop a Cox proportional hazards model using stepwise backward elimination and bootstrapping to correct for optimism. For validation purposes, FFPE ccRCC tissue of 64 patients from the University Hospitals Leuven and a series of 232 cases from The Cancer Genome Atlas (TCGA) were used.

RESULTS

Methylation of GREM1, GATA5, LAD1, NEFH, NEURL, and SFRP1 was associated with poor ccRCC-specific survival, independent of age, sex, tumor size, TNM stage or tumor grade. Moreover, the association between GREM1, NEFH, and NEURL methylation and outcome was shown to be dependent on the genomic region. A prognostic biomarker model containing GREM1, GATA5, LAD1, NEFH and NEURL methylation in combination with clinicopathological characteristics, performed better compared to the model with clinicopathological characteristics only (clinical model), in both the NLCS and the validation population with a c-statistic of 0.71 versus 0.65 and a c-statistic of 0.95 versus 0.86 consecutively. However, the biomarker model had limited added prognostic value in the TCGA series with a c-statistic of 0.76 versus 0.75 for the clinical model.

CONCLUSION

In this study we performed a head-to-head comparison of potential prognostic methylation markers for ccRCC using a novel approach to guide primers design which utilizes the optimal location for measuring DNA methylation. Using this approach, we identified five methylation markers that potentially show prognostic value in addition to currently known clinicopathological factors.

A New Approach to Identify the Methylation Sites in the Control Region of Mitochondrial DNA

Mitochondrial DNA (mtDNA) methylation has the potential to be used as a biomarker of human development or disease. However, mtDNA methylation procedures are costly and time-consuming. Therefore, we developed a new approach based on an RT-PCR assay for the base site identification of methylated cytosine in the control region of mtDNA through a simple, fast, specific, and low-cost strategy. Total DNA was purified, and methylation was determined by RT-PCR bisulfite sequencing. This procedure included the DNA purification, bisulfite treatment and RT-PCR amplification of the control region divided into three subregions with specific primers. Sequences obtained with and without the bisulfite treatment were compared to identify the methylated cytosine dinucleotides. Furthermore, the efficiency of C to U conversion of cytosines was assessed by including a negative control. Interestingly, mtDNA methylation was observed mainly within non-Cphosphate- G (non-CpG) dinucleotides and mostly in the regions containing regulatory elements, such as OH or CSBI, CSBII, and CSBIII. This new approach will promote the generation of new information regarding mtDNA methylation patterns in samples from patients with different pathologies or that are exposed to a toxic environment in diverse human populations.

Genetic Background Effects on the Expression of an Odorant Receptor Gene

There are more than 1000 odorant receptor (OR) genes in the mouse genome. Each olfactory sensory neuron expresses only one of these genes, in a monoallelic fashion. The transcript abundance of homologous OR genes vary between distinct mouse strains. Here we analyzed the expression of the OR gene Olfr17 (also named P2) in different genomic contexts. Olfr17 is expressed at higher levels in the olfactory epithelium from 129 mice than from C57BL/6 (B6) mice. However, we found that in P2-IRES-tauGFP knock-in mice, the transcript levels of the 129 Olfr17 allele are highly reduced when compared to the B6 Olfr17 allele. To address the mechanisms involved in this variation we compared the 5′ region sequence and DNA methylation patterns of the B6 and 129 Olfr17 alleles. Our results show that genetic variations in cis regulatory regions can lead to differential DNA methylation frequencies in these OR gene alleles. They also show that expression of the Olfr17 alleles is largely affected by the genetic background, and suggest that in knock-in mice, expression can be affected by epigenetic modifications in the region of the targeted locus.

Epigenomics and the kidney

PURPOSE OF REVIEW

Epigenetic modifications are reversible changes to a cell's DNA or histones that alter gene expression but not DNA sequence. The present review will explore epigenomic profiling and bioinformatics techniques for the study of kidney development and disease.

RECENT FINDINGS

Reversible DNA and histone modifications influence chromatin accessibility and can be measured by a variety of recent techniques including DNase-seq, ATAC-seq, and single cell ATAC-seq. These approaches have been used to demonstrate that DNA methylation is critical for nephron progenitor maturation, for example. New bioinformatics techniques allow the prediction of chromatin loops that connect regulatory elements to target genes. Recent studies have demonstrated that DNA elements regulate transcription in the kidney via long-range physical interactions and create a new framework for understanding how genome wide association studies risk loci contribute to kidney disease. Increasingly, epigenomic approaches are being combined with transcriptomic analyses to generate multimodal datasets.

SUMMARY

Epigenomics has expanded our knowledge of gene architecture and regulation. Novel tools and techniques have led to the emergence of 'multiomics' in which epigenomic profiling, transcriptomics, and additional methods complement each other to improve our understanding of kidney disease and development.

geno5mC: A Database to Explore the Association between Genetic Variation (SNPs) and CpG Methylation in the Human Genome

Genetic variation, gene expression and DNA methylation influence each other in a complex way. To study the impact of sequence variation and DNA methylation on gene expression, we generated geno⁵mC, a database that contains statistically significant SNP-CpG associations that are biologically classified either through co-localization with known regulatory regions (promoters and enhancers), or through known correlations with the expression levels of nearby genes. The SNP rs727563 can be used to illustrate the usefulness of this approach. This SNP has been associated with inflammatory bowel disease through GWAS, but it is not located near any gene related to this phenotype. However, geno⁵mC reveals that rs727563 is associated with the methylation state of several CpGs located in promoter regions of genes reported to be involved in inflammatory processes. This case exemplifies how geno⁵mC can be used to infer relevant and previously unknown interactions between described disease-associated SNPs and their functional targets.

Molecular Pap Smear: Validation of HPV Genotype and Host Methylation Profiles of ADCY8, CDH8, and ZNF582 as a Predictor of Cervical Cytopathology

Primary high-risk Human Papillomavirus (hrHPV) screening has recently become an accepted standalone or co-test with conventional cytology. Unfortunately, hrHPV singularly lacks specificity for cytopathological grade. However, mechanisms and markers of evolving virus-host interactions at the epigenome level may be harnessed as a better predictor of carcinogenesis. This study aimed to validate and expand the clinical performance of a multiparametric biomarker panel, referred to as the "Molecular Pap smear" based, on HPV genotype and ADCY8, CDH8 and ZNF582 CpG-methylation as a predictive classifier of cervical cytology. This prospective, cross-sectional study used an independent cohort of residual liquid-based cytology for HPV genotyping and epigenetic analysis. Extracted DNA underwent parallel PCR using 3 primer sets for HPV DNA amplification. HPV-infected samples were genotyped by Sanger sequencing. Promoter methylation levels of 3 tumor suppressor genes were quantified by bisulfite-pyrosequencing of genomic DNA on the newest high-resolution PyroMark Q48 platform. Logistic model performance was compared, and model parameters were used to predict and classify binary cytological outcomes. A total of 883 samples were analyzed. HPV DNA positivity correlated with worsening grade: 125/237 (53%) NILM; 136/235 (58%) ASCUS; 222/229 (97%) LSIL; and 157/182 (86%) HSIL samples. The proportion of carcinogenic HPV-types in PCR-positive sequenceable samples correlated with worsening grade: NILM 34/98 (35%); ASCUS 50/113 (44%); LSIL 92/214 (43%); HSIL 129/152 (85%). Additionally, ADCY8, CDH8, and ZNF582 methylation levels increased in direct correlation with worsening grade. Overall, the multi-marker modeling parameters predicted binarized cytological outcomes better than HPV-type alone with significantly higher area under the receiver operator curve (AUC)s, respectively: NILM vs. > NILM (AUC 0.728 vs. 0.709); NILM/ASCUS vs. LSIL/HSIL (AUC 0.805 vs. 0.776); and Collapse

Key Words

• DNA methylation
• carcinogenesis
• epigenetic modification
• evolution
• host-pathogen interactions
• human papillomavirus infection
• pap smear
• pyrosequencing

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Affiliation(s)

Jane Shen-Gunther Gynecologic Oncology & Clinical Investigation, Department of Clinical Investigation, Brooke Army Medical Center, Fort Sam Houston, TX, United States Department of Molecular Medicine, Cancer Therapy and Research Center, University of Texas Health Science Center at San Antonio, San Antonio, TX, United States
Qingqing Xia Department of Clinical Investigation, Brooke Army Medical Center, Fort Sam Houston, TX, United States
Winfred Stacey Department of Clinical Investigation, Brooke Army Medical Center, Fort Sam Houston, TX, United States
Heisy B. Asusta Department of Obstetrics and Gynecology, Brooke Army Medical Center, Fort Sam Houston, TX, United States

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DNA methylation changes in clonally propagated oil palm

Several hypomethylated sites within the Karma region of EgDEF1 and hotspot regions in chromosomes 1, 2, 3, and 5 may be associated with mantling. One of the main challenges faced by the oil palm industry is fruit abnormalities, such as the "mantled" phenotype that can lead to reduced yields. This clonal abnormality is an epigenetic phenomenon and has been linked to the hypomethylation of a transposable element within the EgDEF1 gene. To understand the epigenome changes in clones, methylomes of clonal oil palms were compared to methylomes of seedling-derived oil palms. Whole-genome bisulfite sequencing data from seedlings, normal, and mantled clones were analyzed to determine and compare the context-specific DNA methylomes. In seedlings, coding and regulatory regions are generally hypomethylated while introns and repeats are extensively methylated. Genes with a low number of guanines and cytosines in the third position of codons (GC₃-poor genes) were increasingly methylated towards their 3' region, while GC₃-rich genes remain demethylated, similar to patterns in other eukaryotic species. Predicted promoter regions were generally hypomethylated in seedlings. In clones, CG, CHG, and CHH methylation levels generally decreased in functionally important regions, such as promoters, 5' UTRs, and coding regions. Although random regions were found to be hypomethylated in clonal genomes, hypomethylation of certain hotspot regions may be associated with the clonal mantling phenotype. Our findings, therefore, suggest other hypomethylated CHG sites within the Karma of EgDEF1 and hypomethylated hotspot regions in chromosomes 1, 2, 3 and 5, are associated with mantling.

Identification of cell type-specific methylation signals in bulk whole genome bisulfite sequencing data

BACKGROUND

The traditional approach to studying the epigenetic mechanism CpG methylation in tissue samples is to identify regions of concordant differential methylation spanning multiple CpG sites (differentially methylated regions). Variation limited to single or small numbers of CpGs has been assumed to reflect stochastic processes. To test this, we developed software, Cluster-Based analysis of CpG methylation (CluBCpG), and explored variation in read-level CpG methylation patterns in whole genome bisulfite sequencing data.

RESULTS

Analysis of both human and mouse whole genome bisulfite sequencing datasets reveals read-level signatures associated with cell type and cell type-specific biological processes. These signatures, which are mostly orthogonal to classical differentially methylated regions, are enriched at cell type-specific enhancers and allow estimation of proportional cell composition in synthetic mixtures and improved prediction of gene expression. In tandem, we developed a machine learning algorithm, Precise Read-Level Imputation of Methylation (PReLIM), to increase coverage of existing whole genome bisulfite sequencing datasets by imputing CpG methylation states on individual sequencing reads. PReLIM both improves CluBCpG coverage and performance and enables identification of novel differentially methylated regions, which we independently validate.

CONCLUSIONS

Our data indicate that, rather than stochastic variation, read-level CpG methylation patterns in tissue whole genome bisulfite sequencing libraries reflect cell type. Accordingly, these new computational tools should lead to an improved understanding of epigenetic regulation by DNA methylation.

Methylation analysis of NPTX2 and SH2D5 genes in chronic migraine: A case–control study

Background:

Methylation of two CpG sites related to neuronal pentraxin II protein (NPTX2) and SH2 domain containing 5 protein (SH2D5), corresponding to two neuroplasticity genes, has been associated to headache chronification. We aimed to investigate the epigenetic modification of these two genes in chronic migraine (CM).

Methods:

We conducted a case–control study in which the DNA of 305 age- and sex-matched subjects classified according to the International Classification of Headache Disorders version beta (ICHD-III β) in CM (109), episodic migraine (EM; n = 98), and healthy controls (HC; 98) was analyzed. Real-time quantitative methylation-specific PCR was performed using specific methylation primers for two representative CpG sites within these genes.

Results:

We found no significant differences in methylation level between CM, EM, and HC in the first exon of the NPTX2 gene nor in the 5′ upstream region of the SH2D5 gene. Methylation level in the first exon of the NPTX2 showed a low correlation with age ( r = 0.266; p < 0.005).

Conclusion:

We did not find methylation level differences in analyzed regions related to NPTX2 and SH2D5 in our CM sample. Despite the potential relevance of neuroplasticity genes in headache chronification, we conclude that CM is a more heterogeneous clinical diagnosis than desired and that an epigenetic marker remains elusive.

Integration of whole-genome DNA methylation data with RNA sequencing data to identify markers for bull fertility

Predicting bull fertility prior to breeding is a current challenge for the dairy industry. The use of molecular biomarkers has been previously assessed. However, the integration of this information has not been performed to extract biologically relevant markers. The goal of this study was to integrate DNA methylation data with previously published RNA-sequencing results in order to identify candidate markers for sire fertility. A total of 1765 differentially methylated cytosines were found between high- and low-fertility sires. Ten genes associated with 11 differentially methylated cytosines were found in a previous study of gene expression between high- and low-fertility sires. Additionally, two of these genes code for proteins found exclusively in bull seminal plasma. Collectively, our results reveal 10 genes that could be used in the future as a panel for predicting bull fertility.

Epigenetic Potential in Native and Introduced Populations of House Sparrows (Passer domesticus)

Epigenetic potential, defined as the capacity for epigenetically-mediated phenotypic plasticity, may play an important role during range expansions. During range expansions, populations may encounter relatively novel challenges while experiencing lower genetic diversity. Phenotypic plasticity via epigenetic potential might be selectively advantageous at the time of initial introduction or during spread into new areas, enabling introduced organisms to cope rapidly with novel challenges. Here, we asked whether one form of epigenetic potential (i.e., the abundance of CpG sites) in three microbial surveillance genes: Toll-like receptors (TLRs) 1B (TLR1B), 2A (TLR2A), and 4 (TLR4) varied between native and introduced house sparrows (Passer domesticus). Using an opportunistic approach based on samples collected from sparrow populations around the world, we found that introduced birds had more CpG sites in TLR2A and TLR4, but not TLR1B, than native ones. Introduced birds also lost more CpG sites in TLR1B, gained more CpG sites in TLR2A, and lost fewer CpG sites in TLR4 compared to native birds. These results were not driven by differences in genetic diversity or population genetic structure, and many CpG sites fell within predicted transcription factor binding sites (TFBS), with losses and gains of CpG sites altering predicted TFBS. Although we lacked statistical power to conduct the most rigorous possible analyses, these results suggest that epigenetic potential may play a role in house sparrow range expansions, but additional work will be critical to elucidating how epigenetic potential affects gene expression and hence phenotypic plasticity at the individual, population, and species levels.

Profiling haplotype specific CpG and CpH methylation within a schizophrenia GWAS locus on chromosome 14 in schizophrenia and healthy subjects

Interrogating DNA methylation within schizophrenia risk loci holds promise to identify mechanisms by which genes influence the disease. Based on the hypothesis that allele specific methylation (ASM) of a single CpG, or perhaps CpH, might mediate or mark the effects of genetic variants on disease risk and phenotypes, we explored haplotype specific methylation levels of individual cytosines within a genomic region harbouring the BAG5, APOPT1 and KLC1 genes in peripheral blood of schizophrenia patients and healthy controls. Three DNA fragments located in promoter, intronic and intergenic areas were studied by single-molecule real-time bisulfite sequencing enabling the analysis of long reads of DNA with base-pair resolution and the determination of haplotypes directly from sequencing data. Among 1,012 cytosines studied, we did not find any site where methylation correlated with the disease or cognitive deficits after correction for multiple testing. At the same time, we determined the methylation profile associated with the schizophrenia risk haplotype within the KLC1 fourth intron and confirmed ASM for cytosines located in the vicinity of rs67899457. These genetically associated DNA methylation variations may be related to the pathophysiological mechanism differentiating the risk and non-risk haplotypes and merit further investigation.

Transcriptional memory in skeletal muscle. Don't forget (to) exercise

Transcriptional memory describes an ancient and highly conserved form of cellular learning that enables cells to benefit from recent experience by retaining a mitotically inheritable but reversible memory of the initial transcriptional response when encountering an environmental or physiological stimulus. Herein, we will review recent progress made in the understanding of how cells can make use of diverse constituents of the epigenetic toolbox to retain a transcriptional memory of past states and perturbations. Specifically, we will outline how these mechanisms will help to improve our understanding of skeletal muscle plasticity in health and disease. We describe the epigenetic road map that allows skeletal muscle fibers to navigate through training-induced adaptation processes, and how epigenetic memory marks can preserve an autobiographical history of lifestyle behavior changes, pathological challenges, and aging. We will further consider some key findings in the field of exercise epigenomics to emphasize major challenges when interpreting dynamic changes in the chromatin landscape in response to acute exercise and training.

Detection and accurate false discovery rate control of differentially methylated regions from whole genome bisulfite sequencing

With recent advances in sequencing technology, it is now feasible to measure DNA methylation at tens of millions of sites across the entire genome. In most applications, biologists are interested in detecting differentially methylated regions, composed of multiple sites with differing methylation levels among populations. However, current computational approaches for detecting such regions do not provide accurate statistical inference. A major challenge in reporting uncertainty is that a genome-wide scan is involved in detecting these regions, which needs to be accounted for. A further challenge is that sample sizes are limited due to the costs associated with the technology. We have developed a new approach that overcomes these challenges and assesses uncertainty for differentially methylated regions in a rigorous manner. Region-level statistics are obtained by fitting a generalized least squares regression model with a nested autoregressive correlated error structure for the effect of interest on transformed methylation proportions. We develop an inferential approach, based on a pooled null distribution, that can be implemented even when as few as two samples per population are available. Here, we demonstrate the advantages of our method using both experimental data and Monte Carlo simulation. We find that the new method improves the specificity and sensitivity of lists of regions and accurately controls the false discovery rate.

Repression of TERRA Expression by Subtelomeric DNA Methylation Is Dependent on NRF1 Binding

Chromosome ends are transcribed into long noncoding telomeric repeat-containing RNA (TERRA) from subtelomeric promoters. A class of TERRA promoters are associated with CpG islands embedded in repetitive DNA tracts. Cytosines in these subtelomeric CpG islands are frequently methylated in telomerase-positive cancer cells, and demethylation induced by depletion of DNA methyltransferases is associated with increased TERRA levels. However, the direct evidence and the underlying mechanism regulating TERRA expression through subtelomeric CpG islands methylation are still to establish. To analyze TERRA regulation by subtelomeric DNA methylation in human cell line (HeLa), we used an epigenetic engineering tool based on CRISPR-dCas9 (clustered regularly interspaced short palindromic repeats - dead CRISPR associated protein 9) associated with TET1 (ten-eleven 1 hydroxylase) to specifically demethylate subtelomeric CpG islands. This targeted demethylation caused an up-regulation of TERRA, and the enhanced TERRA production depended on the methyl-sensitive transcription factor NRF1 (nuclear respiratory factor 1). Since AMPK (AMP-activated protein kinase) is a well-known activator of NRF1, we treated cells with an AMPK inhibitor (compound C). Surprisingly, compound C treatment increased TERRA levels but did not inhibit AMPK activity in these experimental conditions. Altogether, our results provide new insight in the fine-tuning of TERRA at specific subtelomeric promoters and could allow identifying new regulators of TERRA.