Genome-scale DNA methylation analysis

Epigenomic insights into common human disease pathology

The epigenome-the chemical modifications and chromatin-related packaging of the genome-enables the same genetic template to be activated or repressed in different cellular settings. This multi-layered mechanism facilitates cell-type specific function by setting the local sequence and 3D interactive activity level. Gene transcription is further modulated through the interplay with transcription factors and co-regulators. The human body requires this epigenomic apparatus to be precisely installed throughout development and then adequately maintained during the lifespan. The causal role of the epigenome in human pathology, beyond imprinting disorders and specific tumour suppressor genes, was further brought into the spotlight by large-scale sequencing projects identifying that mutations in epigenomic machinery genes could be critical drivers in both cancer and developmental disorders. Abrogation of this cellular mechanism is providing new molecular insights into pathogenesis. However, deciphering the full breadth and implications of these epigenomic changes remains challenging. Knowledge is accruing regarding disease mechanisms and clinical biomarkers, through pathogenically relevant and surrogate tissue analyses, respectively. Advances include consortia generated cell-type specific reference epigenomes, high-throughput DNA methylome association studies, as well as insights into ageing-related diseases from biological 'clocks' constructed by machine learning algorithms. Also, 3rd-generation sequencing is beginning to disentangle the complexity of genetic and DNA modification haplotypes. Cell-free DNA methylation as a cancer biomarker has clear clinical utility and further potential to assess organ damage across many disorders. Finally, molecular understanding of disease aetiology brings with it the opportunity for exact therapeutic alteration of the epigenome through CRISPR-activation or inhibition.

Widespread effects of DNA methylation and intra-motif dependencies revealed by novel transcription factor binding models

Several studies suggested that transcription factor (TF) binding to DNA may be impaired or enhanced by DNA methylation. We present MeDeMo, a toolbox for TF motif analysis that combines information about DNA methylation with models capturing intra-motif dependencies. In a large-scale study using ChIP-seq data for 335 TFs, we identify novel TFs that show a binding behaviour associated with DNA methylation. Overall, we find that the presence of CpG methylation decreases the likelihood of binding for the majority of methylation-associated TFs. For a considerable subset of TFs, we show that intra-motif dependencies are pivotal for accurately modelling the impact of DNA methylation on TF binding. We illustrate that the novel methylation-aware TF binding models allow to predict differential ChIP-seq peaks and improve the genome-wide analysis of TF binding. Our work indicates that simplistic models that neglect the effect of DNA methylation on DNA binding may lead to systematic underperformance for methylation-associated TFs.

Technologies and applications of single-cell DNA methylation sequencing

DNA methylation is the most stable epigenetic modification. In mammals, it usually occurs at the cytosine of CpG dinucleotides. DNA methylation is essential for many physiological and pathological processes. Aberrant DNA methylation has been observed in human diseases, particularly cancer. Notably, conventional DNA methylation profiling technologies require a large amount of DNA, often from a heterogeneous cell population, and provide an average methylation level of many cells. It is often not realistic to collect sufficient numbers of cells, such as rare cells and circulating tumor cells in peripheral blood, for bulk sequencing assays. It is therefore essential to develop sequencing technologies that can accurately profile DNA methylation using small numbers of cells or even single cells. Excitingly, many single-cell DNA methylation sequencing and single-cell omics sequencing technologies have been developed, and applications of these methods have greatly expanded our understanding of the molecular mechanism of DNA methylation. Here, we summaries single-cell DNA methylation and multi-omics sequencing methods, delineate their applications in biomedical sciences, discuss technical challenges, and present our perspective on future research directions.

Melatonin and cancer suppression: insights into its effects on DNA methylation

Melatonin is an important naturally occurring hormone in mammals. Melatonin-mediated biological effects include the regulation of circadian rhythms, which is important for optimal human health. Also, melatonin has a broad range of immunoenhancing actions. Moreover, its oncostatic properties, especially regarding breast cancer, involve a variety cancer-inhibitory processes and are well documented. Due to their promising effects on the prognosis of cancer patients, anti-cancer drugs with epigenetic actions have attracted a significant amount of attention in recent years. Epigenetic modifications of cancers are categorized into three major processes including non-coding RNAs, histone modification, and DNA methylation. Hence, the modification of the latter epigenetic event is currently considered an effective strategy for treatment of cancer patients. Thereby, this report summarizes the available evidence that investigated melatonin-induced effects in altering the status of DNA methylation in different cancer cells and models, e.g., malignant glioma and breast carcinoma. Also, we discuss the role of artificial light at night (ALAN)-mediated inhibitory effects on melatonin secretion and subsequent impact on global DNA methylation of cancer cells.

Experimental and Computational Approaches for Non-CpG Methylation Analysis

Cytosine methylation adjacent to adenine, thymine, and cytosine residues but not guanine of the DNA is distinctively known as non-CpG methylation. This CA/CT/CC methylation accounts for 15% of the total cytosine methylation and varies among different cell and tissue types. The abundance of CpG methylation has largely concealed the role of non-CpG methylation. Limitations in the early detection methods could not distinguish CpG methylation from non-CpG methylation. Recent advancements in enrichment strategies and high throughput sequencing technologies have enabled the detection of non-CpG methylation. This review discusses the advanced experimental and computational approaches to detect and describe the genomic distribution and function of non-CpG methylation. We present different approaches such as enzyme-based and antibody-based enrichment, which, when coupled, can also improve the sensitivity and specificity of non-CpG detection. We also describe the current bioinformatics pipelines and their specific application in computing and visualizing the imbalance of CpG and non-CpG methylation. Enrichment modes and the computational suites need to be further developed to ease the challenges of understanding the functional role of non-CpG methylation.

Epigenomics as Potential Tools for Enhancing Magnitude of Breeding Approaches for Developing Climate Resilient Chickpea

Epigenomics has become a significant research interest at a time when rapid environmental changes are occurring. Epigenetic mechanisms mainly result from systems like DNA methylation, histone modification, and RNA interference. Epigenetic mechanisms are gaining importance in classical genetics, developmental biology, molecular biology, cancer biology, epidemiology, and evolution. Epigenetic mechanisms play important role in the action and interaction of plant genes during development, and also have an impact on classical plant breeding programs, inclusive of novel variation, single plant heritability, hybrid vigor, plant-environment interactions, stress tolerance, and performance stability. The epigenetics and epigenomics may be significant for crop adaptability and pliability to ambient alterations, directing to the creation of stout climate-resilient elegant crop cultivars. In this review, we have summarized recent progress made in understanding the epigenetic mechanisms in plant responses to biotic and abiotic stresses and have also tried to provide the ways for the efficient utilization of epigenomic mechanisms in developing climate-resilient crop cultivars, especially in chickpea, and other legume crops.

Nucleosome-Omics: A Perspective on the Epigenetic Code and 3D Genome Landscape

Genetic information is loaded on chromatin, which involves DNA sequence arrangement and the epigenetic landscape. The epigenetic information including DNA methylation, nucleosome positioning, histone modification, 3D chromatin conformation, and so on, has a crucial impact on gene transcriptional regulation. Out of them, nucleosomes, as basal chromatin structural units, play an important central role in epigenetic code. With the discovery of nucleosomes, various nucleosome-level technologies have been developed and applied, pushing epigenetics to a new climax. As the underlying methodology, next-generation sequencing technology has emerged and allowed scientists to understand the epigenetic landscape at a genome-wide level. Combining with NGS, nucleosome-omics (or nucleosomics) provides a fresh perspective on the epigenetic code and 3D genome landscape. Here, we summarized and discussed research progress in technology development and application of nucleosome-omics. We foresee the future directions of epigenetic development at the nucleosome level.

DNA Methylation Malleability and Dysregulation in Cancer Progression: Understanding the Role of PARP1

Mammalian genomic DNA methylation represents a key epigenetic modification and its dynamic regulation that fine-tunes the gene expression of multiple pathways during development. It maintains the gene expression of one generation of cells; particularly, the mitotic inheritance of gene-expression patterns makes it the key governing mechanism of epigenetic change to the next generation of cells. Convincing evidence from recent discoveries suggests that the dynamic regulation of DNA methylation is accomplished by the enzymatic action of TET dioxygenase, which oxidizes the methyl group of cytosine and activates transcription. As a result of aberrant DNA modifications, genes are improperly activated or inhibited in the inappropriate cellular context, contributing to a plethora of inheritable diseases, including cancer. We outline recent advancements in understanding how DNA modifications contribute to tumor suppressor gene silencing or oncogenic-gene stimulation, as well as dysregulation of DNA methylation in cancer progression. In addition, we emphasize the function of PARP1 enzymatic activity or inhibition in the maintenance of DNA methylation dysregulation. In the context of cancer remediation, the impact of DNA methylation and PARP1 pharmacological inhibitors, and their relevance as a combination therapy are highlighted.

Single-molecule, hybridization-based strategies for short nucleic acids detection and recognition with nanopores

DNA nanotechnology has seen large developments over the last 30 years through the combination of detection and discovery of DNAs, and solid phase synthesis to increase the chemical functionalities on nucleic acids, leading to the emergence of novel and sophisticated in features, nucleic acids-based biopolymers. Arguably, nanopores developed for fast and direct detection of a large variety of molecules, are part of a revolutionary technological evolution which led to cheaper, smaller and considerably easier to use devices enabling DNA detection and sequencing at the single-molecule level. Through their versatility, the nanopore-based tools proved useful biomedicine, nanoscale chemistry, biology and physics, as well as other disciplines spanning materials science to ecology and anthropology. This mini-review discusses the progress of nanopore- and hybridization-based DNA detection, and explores a range of state-of-the-art applications afforded through the combination of certain synthetically-derived polymers mimicking nucleic acids and nanopores, for the single-molecule biophysics on short DNA structures.

A Luciferase-EGFP Reporter System for the Evaluation of DNA Methylation in Mammalian Cells

DNA methylation is an essential epigenetic modification involved in numerous biological processes. Here, we present a cell-based system pLTR-Luc2P-EGFP for evaluation of DNA methylation in mammalian cells. In this system, the expression of reporter gene luciferase2P (Luc2P)-EGFP is under the control of HIV-1 promoter 5' long terminal repeat (LTR), which contains multiple CpG sites. Once these sites are methylated, the expression of Luc2P-EGFP is turned off, which may be visualized under fluorescence microscopy, with quantification performed in luciferase activity assay. As a proof of principle, pLTR-Luc2P-EGFP was methylated in vitro, and transfected into 293T cells, where the reduction of Luc2P-EGFP expression was confirmed. Premixed reporter DNA samples with the methylation levels varying from 0 to 100% were used for quantitative measurements of DNA methylation. The resulting standard curves indicated the accuracy of luciferase activity exceeding that of the Western blotting against EGFP. The Bland–Altman analysis showed that data from luciferase activity assay were in good agreement with the actual DNA methylation levels. In summary, we have established a reporter system coupled with reliable detection technique capable of efficient quantifying the changes in methylation in mammalian cells. This system may be utilized as a high throughput screening tool for identifying molecules that modulate DNA methylation.

Interspecific Variation in One-Carbon Metabolism within the Ovarian Follicle, Oocyte, and Preimplantation Embryo: Consequences for Epigenetic Programming of DNA Methylation

One-carbon (1C) metabolism provides methyl groups for the synthesis and/or methylation of purines and pyrimidines, biogenic amines, proteins, and phospholipids. Our understanding of how 1C pathways operate, however, pertains mostly to the (rat) liver. Here we report that transcripts for all bar two genes (i.e., BHMT, MAT1A) encoding enzymes in the linked methionine-folate cycles are expressed in all cell types within the ovarian follicle, oocyte, and blastocyst in the cow, sheep, and pig; as well as in rat granulosa cells (GCs) and human KGN cells (a granulosa-like tumor cell line). Betaine-homocysteine methyltransferase (BHMT) protein was absent in bovine theca and GCs, as was activity of this enzyme in GCs. Mathematical modeling predicted that absence of this enzyme would lead to more volatile S-adenosylmethionine-mediated transmethylation in response to 1C substrate (e.g., methionine) or cofactor provision. We tested the sensitivity of bovine GCs to reduced methionine (from 50 to 10 µM) and observed a diminished flux of 1C units through the methionine cycle. We then used reduced-representation bisulfite sequencing to demonstrate that this reduction in methionine during bovine embryo culture leads to genome-wide alterations to DNA methylation in >1600 genes, including a cohort of imprinted genes linked to an abnormal fetal-overgrowth phenotype. Bovine ovarian and embryonic cells are acutely sensitive to methionine, but further experimentation is required to determine the significance of interspecific variation in BHMT expression.

Liquid Biopsy of Methylation Biomarkers in Cell-Free DNA

Liquid biopsies, in particular, analysis of cell-free DNA (cfDNA), have emerged as a promising noninvasive diagnostic approach in oncology. Abnormal distribution of DNA methylation is one of the hallmarks of many cancers and methylation changes occur early during carcinogenesis. Systemic analysis of cfDNA methylation profiles is being developed for cancer early detection, monitoring for minimal residual disease (MRD), predicting treatment response and prognosis, and tracing the tissue origin. This review highlights the advantages and disadvantages of ctDNA profiling for noninvasive diagnosis of early-stage cancers and explores recent advances in the clinical application of ctDNA methylation assays. We also summarize the technologies for ctDNA methylation analysis and provide a brief overview of the bioinformatic approaches for analyzing DNA methylation sequencing data.

Genome-Wide DNA Methylation Changes of Perirenal Adipose Tissue in Rabbits Fed a High-Fat Diet

DNA methylation is an epigenetic mechanism that plays an important role in gene regulation without an altered DNA sequence. Previous studies have demonstrated that diet affects obesity by partially mediating DNA methylation. Our study investigated the genome-wide DNA methylation of perirenal adipose tissue in rabbits to identify the epigenetic changes of high-fat diet-mediated obesity. Two libraries were constructed pooling DNA of rabbits fed a standard normal diet (SND) and DNA of rabbits fed a high-fat diet (HFD). Differentially methylated regions (DMRs) were identified using the option of the sliding window method, and online software DAVID Bioinformatics Resources 6.7 was used to perform Gene Ontology (GO) terms and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway enrichment analysis of DMRs-associated genes. A total of 12,230 DMRs were obtained, of which 2305 (1207 up-regulated, 1098 down-regulated) and 601 (368 up-regulated, 233 down-regulated) of identified DMRs were observed in the gene body and promoter regions, respectively. GO analysis revealed that the DMRs-associated genes were involved in developmental process (GO:0032502), cell differentiation (GO:0030154), and lipid binding (GO:0008289), and KEGG pathway enrichment analysis revealed the DMRs-associated genes were enriched in linoleic acid metabolism (KO00591), DNA replication (KO03030), and MAPK signaling pathway (KO04010). Our study further elucidates the possible functions of DMRs-associated genes in rabbit adipogenesis, contributing to the understanding of HFD-mediated obesity.

Expression Changes in Epigenetic Gene Pathways Associated With One-Carbon Nutritional Metabolites in Maternal Blood From Pregnancies Resulting in Autism and Non-Typical Neurodevelopment

The prenatal period is a critical window for the development of autism spectrum disorder (ASD). The relationship between prenatal nutrients and gestational gene expression in mothers of children later diagnosed with ASD or non-typical development (Non-TD) is poorly understood. Maternal blood collected prospectively during pregnancy provides insights into the effects of nutrition, particularly one-carbon metabolites, on gene pathways and neurodevelopment. Genome-wide transcriptomes were measured with microarrays in 300 maternal blood samples in Markers of Autism Risk in Babies-Learning Early Signs. Sixteen different one-carbon metabolites, including folic acid, betaine, 5'-methyltretrahydrofolate (5-MeTHF), and dimethylglycine (DMG) were measured. Differential expression analysis and weighted gene correlation network analysis (WGCNA) were used to compare gene expression between children later diagnosed as typical development (TD), Non-TD and ASD, and to one-carbon metabolites. Using differential gene expression analysis, six transcripts (TGR-AS1, SQSTM1, HLA-C, and RFESD) were associated with child outcomes (ASD, Non-TD, and TD) with genome-wide significance. Genes nominally differentially expressed between ASD and TD significantly overlapped with seven high confidence ASD genes. WGCNA identified co-expressed gene modules significantly correlated with 5-MeTHF, folic acid, DMG, and betaine. A module enriched in DNA methylation functions showed a suggestive protective association with folic acid/5-MeTHF concentrations and ASD risk. Maternal plasma betaine and DMG concentrations were associated with a block of co-expressed genes enriched for adaptive immune, histone modification, and RNA processing functions. These results suggest that the prenatal maternal blood transcriptome is a sensitive indicator of gestational one-carbon metabolite status and changes relevant to children's later neurodevelopmental outcomes. LAY SUMMARY: Pregnancy is a time when maternal nutrition could interact with genetic risk for autism spectrum disorder. Blood samples collected during pregnancy from mothers who had a prior child with autism were examined for gene expression and nutrient metabolites, then compared to the diagnosis of the child at age three. Expression differences in gene pathways related to the immune system and gene regulation were observed for pregnancies of children with autism and non-typical neurodevelopment and were associated with maternal nutrients.

Transcriptomic and epigenomic effects of insoluble particles on J774 macrophages

Here we report epigenomic and transcriptomic changes in a prototypical J774 macrophage after engulfing talc or titanium dioxide particles in presence of estrogen. Macrophages are the first immune cells to engage and clear particles of various nature. A novel paradigm is emerging, that exposure to so-called 'inert' particulates that are considered innocuous is not really free of consequences. We hypothesized that especially the insoluble, non-digestible particles that do not release a known hazardous chemical can be underappreciated agents acting to affect the regulation inside macrophages upon phagocytosis. We performed gene chip microarray profiling and found that talc alone, and especially with oestrogen, has induced a substantially more prominent gene expression change than titanium dioxide; the affected genes were involved in pathways of cell proliferation, immune response and regulation, and, unexpectedly, enzymes and proteins of epigenetic regulation. We therefore tested the DNA methylation profiles of these cells via epigenome-wide bisulphite sequencing and found vast epigenetic changes in hundreds of loci, remarkably after a very short exposure to particles; ELISA assay for methylcytosine levels determined the particles induced an overall decrease in DNA methylation. We found a few loci where both the transcriptional changes and epigenetic changes occurred in the pathways involving immune and inflammatory signalling. Some transcriptomic and epigenomic changes were shared between talc and titanium dioxide, however, it is especially interesting that each of the two particles of similar size and insoluble nature has also induced a specific pattern of gene expression and DNA methylation changes which we report here.

Perspectives on the Role of Histone Modification in Breast Cancer Progression and the Advanced Technological Tools to Study Epigenetic Determinants of Metastasis

Metastasis is a complex process that involved in various genetic and epigenetic alterations during the progression of breast cancer. Recent evidences have indicated that the mutation in the genome sequence may not be the key factor for increasing metastatic potential. Epigenetic changes were revealed to be important for metastatic phenotypes transition with the development in understanding the epigenetic basis of breast cancer. Herein, we aim to present the potential epigenetic drivers that induce dysregulation of genes related to breast tumor growth and metastasis, with a particular focus on histone modification including histone acetylation and methylation. The pervasive role of major histone modification enzymes in cancer metastasis such as histone acetyltransferases (HAT), histone deacetylases (HDACs), DNA methyltransferases (DNMTs), and so on are demonstrated and further discussed. In addition, we summarize the recent advances of next-generation sequencing technologies and microfluidic-based devices for enhancing the study of epigenomic landscapes of breast cancer. This feature also introduces several important biotechnologists for identifying robust epigenetic biomarkers and enabling the translation of epigenetic analyses to the clinic. In summary, a comprehensive understanding of epigenetic determinants in metastasis will offer new insights of breast cancer progression and can be achieved in the near future with the development of innovative epigenomic mapping tools.

Hypermethylation of Auxin-Responsive Motifs in the Promoters of the Transcription Factor Genes Accompanies the Somatic Embryogenesis Induction in Arabidopsis

The auxin-induced embryogenic reprogramming of plant somatic cells is associated with extensive modulation of the gene expression in which epigenetic modifications, including DNA methylation, seem to play a crucial role. However, the function of DNA methylation, including the role of auxin in epigenetic regulation of the SE-controlling genes, remains poorly understood. Hence, in the present study, we analysed the expression and methylation of the TF genes that play a critical regulatory role during SE induction (LEC1, LEC2, BBM, WUS and AGL15) in auxin-treated explants of Arabidopsis. The results showed that auxin treatment substantially affected both the expression and methylation patterns of the SE-involved TF genes in a concentration-dependent manner. The auxin treatment differentially modulated the methylation of the promoter (P) and gene body (GB) sequences of the SE-involved genes. Relevantly, the SE-effective auxin treatment (5.0 µM of 2,4-D) was associated with the stable hypermethylation of the P regions of the SE-involved genes and a significantly higher methylation of the P than the GB fragments was a characteristic feature of the embryogenic culture. The presence of auxin-responsive (AuxRE) motifs in the hypermethylated P regions suggests that auxin might substantially contribute to the DNA methylation-mediated control of the SE-involved genes.

Pharmacoepigenetics and Pharmacoepigenomics: An Overview

BACKGROUND

The rapid and major advances being made in epigenetics are impacting pharmacology, giving rise to new sub-disciplines in pharmacology, pharmacoepigenetics, the study of the epigenetic basis of variation in response to drugs; and pharmacoepigenomics, the application of pharmacoepigenetics on a genome-wide scale.

METHODS

This article highlights the following aspects of pharmacoepigenetics and pharmacoepigenomics: epigenetic therapy, the role of epigenetics in pharmacokinetics, the relevance of epigenetics to adverse drug reactions, personalized medicine, drug addiction, and drug resistance, and the use of epigenetic biomarkers in drug therapy.

RESULTS

Epigenetics is having an increasing impact on several areas of pharmacology.

CONCLUSION

Pharmacoepigenetics and pharmacoepigenomics are new sub-disciplines in pharmacology and are likely to have an increasing impact on the use of drugs in clinical practice.

The role of epigenetics and non-coding RNAs in autophagy: A new perspective for thorough understanding

Autophagy is a major self-degradative intracellular process required for the maintenance of homeostasis and promotion of survival in response to starvation. It plays critical roles in a large variety of physiological and pathological processes. On the other hand, aberrant regulation of autophagy can lead to various cancers and neurodegenerative diseases such as Alzheimer's disease, Parkinson's disease, and Crohn's disease. Emerging evidence strongly supports that epigenetic signatures, related non-coding RNA profiles, and their cross-talking are significantly associated with the control of autophagic responses. Therefore, it may be helpful and promising to manage autophagic processes by finding valuable markers and therapeutic approaches. Although there is a great deal of information on the components of autophagy in the cytoplasm, the molecular basis of the epigenetic regulation of autophagy has not been completely elucidated. In this review, we highlight recent research on epigenetic changes through the expression of autophagy-related genes (ATGs), which regulate autophagy, DNA methylation, histone modifications as well as non-coding RNAs, including long non-coding RNAs (lncRNAs), microRNAs (miRNAs) and their relationship with human diseases, that play key roles in causing autophagy-related diseases.

Epigenetic-sensitive pathways in personalized therapy of major cardiovascular diseases

The complex pathobiology underlying cardiovascular diseases (CVDs) has yet to be explained. Aberrant epigenetic changes may result from alterations in enzymatic activities, which are responsible for putting in and/or out the covalent groups, altering the epigenome and then modulating gene expression. The identification of novel individual epigenetic-sensitive trajectories at single cell level might provide additional opportunities to establish predictive, diagnostic and prognostic biomarkers as well as drug targets in CVDs. To date, most of studies investigated DNA methylation mechanism and miRNA regulation as epigenetics marks. During atherogenesis, big epigenetic changes in DNA methylation and different ncRNAs, such as miR-93, miR-340, miR-433, miR-765, CHROME, were identified into endothelial cells, smooth muscle cells, and macrophages. During man development, lipid metabolism, inflammation and homocysteine homeostasis, alter vascular transcriptional mechanism of fundamental genes such as ABCA1, SREBP2, NOS, HIF1. At histone level, increased HDAC9 was associated with matrix metalloproteinase 1 (MMP1) and MMP2 expression in pro-inflammatory macrophages of human carotid plaque other than to have a positive effect on toll like receptor signaling and innate immunity. HDAC9 deficiency promoted inflammation resolution and reverse cholesterol transport, which might block atherosclerosis progression and promote lesion regression. Here, we describe main human epigenetic mechanisms involved in atherosclerosis, coronary heart disease, ischemic stroke, peripheral artery disease; cardiomyopathy and heart failure. Different epigenetics mechanisms are activated, such as regulation by circular RNAs, as MICRA, and epitranscriptomics at RNA level. Moreover, in order to open new frontiers for precision medicine and personalized therapy, we offer a panoramic view on the most innovative bioinformatic tools designed to identify putative genes and molecular networks underlying CVDs in man.

The structure of the Thermococcus gammatolerans McrB N-terminal domain reveals a new mode of substrate recognition and specificity among McrB homologs

McrBC is a two-component, modification-dependent restriction system that cleaves foreign DNA-containing methylated cytosines. Previous crystallographic studies have shown that Escherichia coli McrB uses a base-flipping mechanism to recognize these modified substrates with high affinity. The side chains stabilizing both the flipped base and the distorted duplex are poorly conserved among McrB homologs, suggesting that other mechanisms may exist for binding modified DNA. Here we present the structures of the Thermococcus gammatolerans McrB DNA-binding domain (TgΔ185) both alone and in complex with a methylated DNA substrate at 1.68 and 2.27 Å resolution, respectively. The structures reveal that TgΔ185 consists of a YT521-B homology (YTH) domain, which is commonly found in eukaryotic proteins that bind methylated RNA and is structurally unrelated to the E. coli McrB DNA-binding domain. Structural superposition and co-crystallization further show that TgΔ185 shares a conserved aromatic cage with other YTH domains, which forms the binding pocket for a flipped-out base. Mutational analysis of this aromatic cage supports its role in conferring specificity for the methylated adenines, whereas an extended basic surface present in TgΔ185 facilitates its preferential binding to duplex DNA rather than RNA. Together, these findings establish a new binding mode and specificity among McrB homologs and expand the biological roles of YTH domains.

DNA Methylation of Candidate Genes (ACE II, IFN-γ, AGTR 1, CKG, ADD1, SCNN1B and TLR2) in Essential Hypertension: A Systematic Review and Quantitative Evidence Synthesis

Physical, chemical, and social environments adversely affect the molecular process and results in cell signal transduction and the subsequent transcription factor dysregulation, leading to impaired gene expression and abnormal protein synthesis. Stressful environments such as social adversity, isolation, sustained social threats, physical inactivity, and highly methylated diets predispose individuals to molecular level alterations such as aberrant epigenomic modulations that affect homeostasis and hemodynamics. With cardiovascular disease as the leading cause of mortality in the US and blacks/African Americans being disproportionately affected by hypertension (HTN) which contributes substantially to these deaths, reflecting the excess mortality and survival disadvantage of this sub-population relative to whites, understanding the molecular events, including epigenomic and socio-epigenomic modulations, is relevant to narrowing the black-white mortality risk differences. We aimed to synthesize epigenomic findings in HTN namely (a) angiotensin-converting enzyme 2 (ACE II) gene, (b) Toll-like receptor 2 (TLR2) gene, (c) interferon γ (IFN-γ) gene, and (d) Capping Actin Protein, Gelosin-Like (CAPG) gene, adducin 1(ADD1) gene, (e) Tissue inhibitor of metalloproteinase 3 (TIMP3), (f) mesoderm specific transcript (MEST) loci, (g) sodium channel epithelial 1 alpha subunit 2 (SCNN1B), (h) glucokinase (CKG) gene (i) angiotensin II receptor, type1 (AGTR1), and DNA methylation (mDNA). A systematic review and quantitative evidence synthesis (QES) was conducted using Google Scholar and PubMed with relevant search terms. Data were extracted from studies on: (a) Epigenomic modulations in HTN based on ACE II (b) TLR2, (c) IFN-γ gene, (d) CAPG, ADD1, TIMP3, MEST loci, and mDNA. The random-effect meta-analysis method was used for a pooled estimate of the common effect size, while z statistic and I^2 were used for the homogeneity of the common effect size and between studies on heterogeneity respectively. Of the 642 studies identified, five examined hypermethylation while seven studies assessed hypomethylation in association with HTN. The hypermethylation of ACE II, SCNN1B, CKG, IFN-γ gene, and miR-510 promoter were associated with hypertension, the common effect size (CES) = 6.0%, 95% CI, −0.002–11.26. In addition, the hypomethylation of TLR2, IFN-γ gene, ADD1, AGTR1, and GCK correlated with hypertension, the CES = 2.3%, 95% CI, −2.51–7.07. The aberrant epigenomic modulation of ACE II, TLR2, IFN-γ, AGTR1, and GCK correlated with essential HTN. Transforming the environments resulting from these epigenomic lesions will facilitate early intervention mapping in reducing HTN in the US population, especially among socially disadvantaged individuals, particularly racial/ethnic minorities.

Chemical Tools with Fluorescence Switches for Verifying Epigenetic Modifications

Epigenetic DNA and histone modifications alter chromatin conformation and regulate gene expression. A major DNA modification is methylation, which is catalyzed by DNA methyltransferase (Dnmt) and results in gene suppression. Compared to DNA, histones undergo a greater variety of modification types, one of which is the acetylation of lysine. While histone acetyltransferase (HAT) catalyzes acetylation and activates gene expression, histone deacetylase (HDAC) removes the modification and causes gene suppression. As precise regulation of these epigenetic marks on DNA and histones is critical for cellular functions, their dysregulation causes various diseases including cancer, metabolic syndromes, immune diseases, and psychiatric diseases. Therefore, elucidation of the epigenetic phenomena is important not only in the field of biology but also in medical and pharmaceutical sciences. Furthermore, this field is also attracting industrial interest, because small-molecule inhibitors modulate enzymatic activity for epigenetic modification and are used for cancer treatment. Under these circumstances, various methods for detecting epigenetic modifications have been developed. However, most methods require cell lysis, which is not suitable for real-time detection of enzymatic activity. Since fluorescent probes are attractive chemical tools to solve this issue, chemists made considerable efforts to create fluorescent probes for epigenetics. To date, we have particularly focused on HDAC activity and DNA methylation and have developed fluorescent probes for their detection. The first part of this review describes our recent efforts to develop fluorescent probes for detecting HDAC activity. Since the discovery of HDAC activity in the late 1960s, no fluorescent probe has been developed that can detect enzymatic reactions in a simple, one-step procedure despite its biological and medical importance. We designed fluorescent probes to overcome this limitation by devising two different types of fluorescence switching mechanisms, which are based on aggregation-induced emission (AIE) and intramolecular transesterification. Using these probes, we detected HDAC activity simply by mixing the probes and HDAC for the first time. In the second part, a hybrid approach using a protein-labeling system was employed to detect DNA methylation in living cells. So far, live-cell detection of DNA methylation was conducted by imaging the localization of Fluorescent Proteins (FPs) fused to a methylated DNA-binding domain. However, FP lacks a fluorescence switch and emits fluorescence without binding to methylated DNA. We created a hybrid probe that comprises a fluorogen and a protein and enhances fluorescence intensity upon binding to methylated DNA. To create the hybrid probe, we applied our protein labeling system using the PYP-tag that we previously developed. This method successfully visualized methylated DNA in living cells and verified its dynamics during cell division. Both of the above-mentioned fluorescent probes have great potential for use not only in HDAC and DNA methylation but also in other epigenetics-associated modifications. For example, the mechanism of the HDAC probes can be used to detect histone demethylation. The hybrid probe can be converted to a sensor for imaging acetylated or methylated histones. In this review, we mainly describe how we designed the probes using chemical principles and solved the current obstacles with the probe design and discuss the future prospects of these probes.

Hexameric assembly of the AAA+ protein McrB is necessary for GTPase activity

McrBC is one of the three modification-dependent restriction enzymes encoded by the Escherichia coli K12 chromosome. Amongst restriction enzymes, McrBC and its close homologues are unique in employing the AAA+ domain for GTP hydrolysis-dependent activation of DNA cleavage. The GTPase activity of McrB is stimulated by the endonuclease subunit McrC. It had been reported previously that McrB and McrC subunits oligomerise together into a high molecular weight species. Here we conclusively demonstrate using size exclusion chromatography coupled multi-angle light scattering (SEC-MALS) and images obtained by electron cryomicroscopy that McrB exists as a hexamer in solution. Furthermore, based on SEC-MALS and SAXS analyses of McrBC and the structure of McrB, we propose that McrBC is a complex of two McrB hexamers bridged by two subunits of McrC, and that the complete assembly of this complex is integral to its enzymatic activity. We show that the nucleotide-dependent oligomerisation of McrB precedes GTP hydrolysis. Mutational studies show that, unlike other AAA+ proteins, the catalytic Walker B aspartate is required for oligomerisation.

Earlier demethylation of myogenic genes contributes to embryonic precocious terminal differentiation of myoblasts in miniature pigs

Here, we performed whole-genome bisulfite sequencing of longissimus dorsi muscle from Landrace and Wuzhishan (WZS) miniature pigs during 18, 21, and 28 d postcoitum. It was uncovered that in regulatory regions only around transcription start sites (TSSs), gene expression and methylation showed negative correlation, whereas in gene bodies, positive correlation occurred. Furthermore, earlier myogenic gene demethylation around TSSs and earlier hypermethylation of myogenic genes in gene bodies were considered to trigger their earlier expression in miniature pigs. Furthermore, by analyzing the methylation pattern of the myogenic differentiation 1(MyoD) promoter and distal enhancer, we found that earlier demethylation of the MyoD distal enhancer in WZSs contributes to its earlier expression. Moreover, DNA demethylase Tet1 was found to be involved in the demethylation of the myogenin promoter and promoted immortalized mouse myoblast cell line (C2C12) and porcine embryonic myogenic cell differentiation. This study reveals that earlier demethylation of myogenic genes contributes to precocious terminal differentiation of myoblasts in miniature pigs.-Zhang, X., Nie, Y., Cai, S., Ding, S., Fu, B., Wei, H., Chen, L., Liu, X., Liu, M., Yuan, R., Qiu, B., He, Z., Cong, P., Chen, Y., Mo, D. Earlier demethylation of myogenic genes contributes to embryonic precocious terminal differentiation of myoblasts in miniature pigs.

Entering the post-epigenomic age: back to epigenetics

It is undeniably one of the greatest findings in biology that (with some very minor exceptions) every cell in the body possesses the whole genetic information needed to generate a complete individual. Today, this concept has been so thoroughly assimilated that we struggle to still see how surprising this finding actually was: all cellular phenotypes naturally occurring in one person are generated from genetic uniformity, and thus are per definition epigenetic. Transcriptional mechanisms are clearly critical for developing and protecting cell identities, because a mis-expression of few or even single genes can efficiently induce inappropriate cellular programmes. However, how transcriptional activities are molecularly controlled and which of the many known epigenomic features have causal roles remains unclear. Today, clarification of this issue is more pressing than ever because profiling efforts and epigenome-wide association studies (EWAS) continuously provide comprehensive datasets depicting epigenomic differences between tissues and disease states. In this commentary, we propagate the idea of a widespread follow-up use of epigenome editing technology in EWAS studies. This would enable them to address the questions of which features, where in the genome, and which circumstances are essential to shape development and trigger disease states.

DNA Methylation Analysis

DNA methylation is a process by which methyl groups are added to cytosine or adenine. DNA methylation can change the activity of the DNA molecule without changing the sequence. Methylation of 5-methylcytosine (5mC) is widespread in both eukaryotes and prokaryotes, and it is a very important epigenetic modification event, which can regulate gene activity and influence a number of key processes such as genomic imprinting, cell differentiation, transcriptional regulation, and chromatin remodeling. Profiling DNA methylation across the genome is critical to understanding the influence of methylation in normal biology and diseases including cancer. Recent discoveries of 5-methylcytosine (5mC) oxidation derivatives including 5-hydroxymethylcytosine (5hmC), 5-formylcytsine (5fC), and 5-carboxycytosine (5caC) in mammalian genome further expand our understanding of the methylation regulation. Genome-wide analyses such as microarrays and next-generation sequencing technologies have been used to assess large fractions of the methylome. A number of different quantitative approaches have also been established to map the DNA epigenomes with single-base resolution, as represented by the bisulfite-based methods, such as classical bisulfite sequencing, pyrosequencing etc. These methods have been used to generate base-resolution maps of 5mC and its oxidation derivatives in genomic samples. The focus of this chapter is to provide the methodologies that have been developed to detect the cytosine derivatives in the genomic DNA.

DNA methylation and gene expression alterations in zebrafish early-life stages exposed to the antibacterial agent triclosan

There is increasing evidence that toxicant exposure can alter DNA methylation profile, one of the main epigenetic mechanisms, particularly during embryogenesis when DNA methylation patterns are being established. In order to investigate the effects of the antibacterial agent Triclosan on DNA methylation and its correlation with gene expression, zebrafish embryos were exposed during 7 days post-fertilization (starting at maximum 8-cells stage) to 50 and 100 μg/l, two conditions for which increased sensitivity and acclimation have been respectively reported. Although global DNA methylation was not significantly affected, a total of 171 differentially methylated fragments were identified by Reduced Representation Bisulfite Sequencing. The majority of these fragments were found between the two exposed groups, reflecting dose-dependant specific responses. Gene ontology analysis revealed that pathways involved in TGF-β signaling were enriched in larvae exposed to 50 μg/l, while de novo pyrimidine biosynthesis functions were overrepresented in fish exposed to 100 μg/l. In addition, gene expression analysis revealed a positive correlation between mRNA levels and DNA methylation patterns in introns, together with significant alterations of the transcription of genes involved in nervous system development, transcriptional factors and histone methyltransferases. Overall this work provides evidence that Triclosan alters DNA methylation in zebrafish exposed during embryogenesis as well as related genes expression and proposes concentration specific modes of action. Further studies will investigate the possible long-term consequences of these alterations, i.e. latent defects associated with developmental exposure and transgenerational effects, and the possible implications in terms of fitness and adaptation to environmental pollutants.

Next-generation sequencing approaches for the study of genome and epigenome toxicity induced by sulfur mustard

Sulfur mustard (SM) is an extensive nucleophilic and alkylating agent that targets different tissues. The genotoxic property of SM is the most threatening effect, because it is associated with detrimental inflammations and susceptibility to several kinds of cancer. Moreover, SM causes a wide variety of adverse effects on DNA which result in accumulation of DNA adducts, multiple mutations, aneuploidies, and epigenetic aberrations in the genome. However, these adverse effects are still not known well, possibly because no valid biomarkers have been developed for detecting them. The advent of next-generation sequencing (NGS) has provided opportunities for the characterization of these alterations with a higher level of molecular detail and cost-effectivity. The present review introduces NGS approaches for the detection of SM-induced DNA adducts, mutations, chromosomal structural variation, and epigenetic aberrations, and also comparing and contrasting them with regard to which might be most advantageous.

A smoothed EM-algorithm for DNA methylation profiles from sequencing-based methods in cell lines or for a single cell type

We consider the assessment of DNA methylation profiles for sequencing-derived data from a single cell type or from cell lines. We derive a kernel smoothed EM-algorithm, capable of analyzing an entire chromosome at once, and to simultaneously correct for experimental errors arising from either the pre-treatment steps or from the sequencing stage and to take into account spatial correlations between DNA methylation profiles at neighbouring CpG sites. The outcomes of our algorithm are then used to (i) call the true methylation status at each CpG site, (ii) provide accurate smoothed estimates of DNA methylation levels, and (iii) detect differentially methylated regions. Simulations show that the proposed methodology outperforms existing analysis methods that either ignore the correlation between DNA methylation profiles at neighbouring CpG sites or do not correct for errors. The use of the proposed inference procedure is illustrated through the analysis of a publicly available data set from a cell line of induced pluripotent H9 human embryonic stem cells and also a data set where methylation measures were obtained for a small genomic region in three different immune cell types separated from whole blood.

Genome-wide DNA methylation profiles of porcine ovaries in estrus and proestrus

DNA methylation is an important epigenetic modification involved in the estrous cycle and the regulation of reproduction. Here, we investigated the genome-wide profiles of DNA methylation in porcine ovaries in proestrus and estrus using methylated DNA immunoprecipitation sequencing. The results showed that DNA methylation was enriched in intergenic and intron regions. The methylation levels of coding regions were higher than those of the 5'- and 3'-flanking regions of genes. There were 4,813 differentially methylated regions (DMRs) of CpG islands in the estrus vs. proestrus ovarian genomes. Additionally, 3,651 differentially methylated genes (DMGs) were identified in pigs in estrus and proestrus. The DMGs were significantly enriched in biological processes and pathways related to reproduction and hormone regulation. We identified 90 DMGs associated with regulating reproduction in pigs. Our findings can serve as resources for DNA methylome research focused on porcine ovaries and further our understanding of epigenetically regulated reproduction in mammals.

Synthetic-Molecule/Protein Hybrid Probe with Fluorogenic Switch for Live-Cell Imaging of DNA Methylation

Hybrid probes consisting of synthetic molecules and proteins are powerful tools for detecting biological molecules and signals in living cells. To date, most targets of the hybrid probes have been limited to pH and small analytes. Although biomacromolecules are essential to the physiological function of cells, the hybrid-probe-based approach has been scarcely employed for live-cell detection of biomacromolecules. Here, we developed a hybrid probe with a chemical switch for live-cell imaging of methylated DNA, an important macromolecule in the repression of gene expression. Using a protein labeling technique, we created a hybrid probe containing a DNA-binding fluorogen and a methylated-DNA-binding domain. The hybrid probe enhanced fluorescence intensity upon binding to methylated DNA and successfully monitored methylated DNA during mitosis. The hybrid probe offers notable advantages absent from probes based on small molecules or fluorescent proteins and is useful for live-cell analyses of epigenetic phenomena and diseases related to DNA methylation.

Microdroplet PCR for Highly Multiplexed Targeted Bisulfite Sequencing

Many methods exist for examining CpG DNA methylation. However, many of these are qualitative, laborious to apply to a large number of genes simultaneously, or are not easy to target to specific regions of interest. Microdroplet PCR-based bisulfite sequencing allows for quantitative single base resolution analysis of investigator selected regions of interest. Following bisulfite conversion of genomic DNA, targeted microdroplet PCR is conducted with custom primer libraries. Samples are then fragmented, concatenated, and sequenced by high-throughput sequencing. The most recent technology allows for this method to be conducted with as little as 250 ng of bisulfite-converted DNA. The primary advantage of this method is the ability to hand-select the targeted regions covered by up to 10,000 amplicons of 500-600 bp. Moreover, the nature of microdroplet PCR virtually eliminates PCR bias and allows for the amplification of all targets simultaneously in a single tube.

A Versatile Assay for Detection of Aberrant DNA Methylation in Bladder Cancer

Urothelial carcinoma of the bladder is one of the most common malignancies in the industrialized world, mainly caused by smoking and occupational exposure to chemicals. The favorable prognosis of early stage bladder cancer underscores the importance of early detection for the treatment of this disease. The high recurrence rate of this malignancy also highlights the need for close post-diagnosis monitoring of bladder cancer patients. As for other malignancies, aberrant DNA methylation has been shown to play a crucial role in the initiation and progression of bladder cancer, and thus holds great promise as a diagnostic and prognostic biological marker. Here, we describe a protocol for a versatile DNA methylation enrichment method, the Methylated CpG Island Recovery Assay (MIRA), which enables analysis of the DNA methylation status in individual genes or across the entire genome. MIRA is based on the ability of the methyl-binding domain (MBD) proteins, the MBD2B/MBD3L1 complex, to specifically bind methylated CpG dinucleotides. This easy-to-perform method can be used to analyze the methylome of bladder cancer or urothelial cells shed in the urine to elucidate the evolution of bladder carcinogenesis and/or identify epigenetic signatures of chemicals known to cause this malignancy.

Comparative analysis of MBD-seq and MeDIP-seq and estimation of gene expression changes in a rodent model of schizophrenia

We conducted a comparative study of multiplexed affinity enrichment sequence methodologies (MBD-seq and MeDIP-seq) in a rodent model of schizophrenia, induced by in utero methylazoxymethanol acetate (MAM) exposure. We also examined related gene expression changes using a pooled sample approach. MBD-seq and MeDIP-seq identified 769 and 1771 differentially methylated regions (DMRs) between F2 offspring of MAM-exposed rats and saline control rats, respectively. The assays showed good concordance, with ~56% of MBD-seq-detected DMRs being identified by or proximal to MeDIP-seq DMRs. There was no significant overlap between DMRs and differentially expressed genes, suggesting that DNA methylation regulatory effects may act upon more distal genes, or are too subtle to detect using our approach. Methylation and gene expression gene ontology enrichment analyses identified biological processes important to schizophrenia pathophysiology, including neuron differentiation, prepulse inhibition, amphetamine response, and glutamatergic synaptic transmission regulation, reinforcing the utility of the MAM rodent model for schizophrenia research.

Current trends in electrochemical sensing and biosensing of DNA methylation

DNA methylation plays an important role in physiological and pathological processes. Several genetic diseases and most malignancies tend to be associated with aberrant DNA methylation. Among other analytical methods, electrochemical approaches have been successfully employed for characterisation of DNA methylation patterns that are essential for the diagnosis and treatment of particular diseases. This article discusses current trends in the electrochemical sensing and biosensing of DNA methylation. Particularly, it provides an overview of applied electrode materials, electrode modifications and biorecognition elements applications with an emphasis on strategies that form the core DNA methylation detection approaches. The three main strategies as (i) bisulfite treatment, (ii) cleavage by restriction endonucleases, and (iii) immuno/affinity reaction were described in greater detail. Additionally, the availability of the reviewed platforms for early cancer diagnosis and the approval of methylation inhibitors for anticancer therapy were discussed.

DNA methylation and its role in the pathogenesis of diabetes

Although the factors responsible for the recent increase in the prevalence of diabetes worldwide are not entirely known, the morbidity associated with this disease results in substantial health and economic burden on society. Epigenetic modifications, including DNA methylation have been identified as one mechanism by which the environment interacts with the genome and there is evidence that alterations in DNA methylation may contribute to the increased prevalence of both type 1 and type 2 diabetes. This review provides a summary of DNA methylation and its role in gene regulation, and includes descriptions of various techniques to measure site-specific and genome-wide DNA methylation changes. In addition, we review current literature highlighting the complex relationship between DNA methylation, gene expression, and the development of diabetes and related complications. In studies where both DNA methylation and gene expression changes were reported, DNA methylation status had a strong inverse correlation with gene expression, suggesting that this interaction may be a potential future therapeutic target. We highlight the emerging use of genome-wide DNA methylation profiles as a biomarker to predict patients at risk of developing diabetes or specific complications of diabetes. The development of a predictive model that incorporates both genetic sequencing and DNA methylation data may be an effective diagnostic approach for all types of diabetes and could lead to additional innovative therapies.

RNAi-based targeted gene knockdown in the model oleaginous microalgae Nannochloropsis oceanica

Microalgae are promising feedstock for renewable fuels such as biodiesel, yet development of industrial oleaginous strains has been hindered by the paucity and inefficiency of reverse genetics tools. Here we established an efficient RNAi-based targeted gene-knockdown method for Nannochloropsis spp., which are emerging model organisms for industrial microalgal oil production. The method achieved a 40-80% success rate in Nannochloropsis oceanica strain IMET1. When transcript level of one carbonic anhydrase (CA) was inhibited by 62-83% via RNAi, mutant cells exhibited photosynthetic oxygen evolution (POE) rates that were 68-100% higher than wild-type (WT) at pH 6.0, equivalent to WT at pH 8.2, yet 39-45% lower than WT at pH 9.0. Moreover, the mutant POE rates were negatively correlated with the increase of culture pH, an exact opposite of WT. Thus, a dynamic carbon concentration mechanism (CCM) that is highly sensitive to pH homeostasis was revealed, where the CA inhibition likely partially abrogated the mechanism that normally deactivates CCM under a high level of dissolved CO₂ . Extension of the method to another sequenced N. oceanica strain of CCMP 1779 demonstrated comparable performance. Finally, McrBC-PCR followed by bisulfite sequencing revealed that the gene knockdown is mediated by the CG, CHG and CHH types of DNA methylation at the coding region of the targeted gene. The efficiency, robustness and general applicability of this reverse genetics approach suggested the possibility of large-scale RNAi-based gene function screening in industrial microalgae.

Procaine Induces Epigenetic Changes in HCT116 Colon Cancer Cells

Colon cancer is the third most commonly diagnosed cancer in the world, and it is the major cause of morbidity and mortality throughout the world. The present study aimed at treating colon cancer cell line (HCT116) with different chemotherapeutic drug/drug combinations (procaine, vorinostat “SAHA,” sodium phenylbutyrate, erlotinib, and carboplatin). Two different final concentrations were applied: 3 μM and 5 μM. Trypan blue test was performed to assess the viability of the cell before and after being treated with the drugs. The data obtained showed that there was a significant decrease in the viability of cells after applying the chemotherapeutic drugs/drug combinations. Also, DNA fragmentation assay was carried out to study the effect of these drugs on the activation of apoptosis-mediated DNA degradation process. The results indicated that all the drugs/drug combinations had a severe effect on inducing DNA fragmentation. Global DNA methylation quantification was performed to identify the role of these drugs individually or in combination in hypo- or hypermethylating the CpG dinucleotide all over the genome of the HCT116 colon cancer cell line. Data obtained indicated that different combinations had different effects in reducing or increasing the level of methylation, which might indicate the effectiveness of combining drugs in treating colon cancer cells.

Genome-wide analysis of DNA methylation in obese, lean, and miniature pig breeds

DNA methylation is a crucial epigenetic modification involved in diverse biological processes. There is significant phenotypic variance between Chinese indigenous and western pig breeds. Here, we surveyed the genome-wide DNA methylation profiles of blood leukocytes from three pig breeds (Tongcheng, Landrace, and Wuzhishan) by methylated DNA immunoprecipitation sequencing. The results showed that DNA methylation was enriched in gene body regions and repetitive sequences. LINE/L1 and SINE/tRNA-Glu were the predominant methylated repeats in pigs. The methylation level in the gene body regions was higher than in the 5' and 3' flanking regions of genes. About 15% of CpG islands were methylated in the pig genomes. Additionally, 2,807, 2,969, and 5,547 differentially methylated genes (DMGs) were identified in the Tongcheng vs. Landrace, Tongcheng vs. Wuzhishan, and Landrace vs. Wuzhishan comparisons, respectively. A total of 868 DMGs were shared by the three contrasts. The DMGs were significantly enriched in development- and metabolism-related biological processes and pathways. Finally, we identified 32 candidate DMGs associated with phenotype variance in pigs. Our research provides a DNA methylome resource for pigs and furthers understanding of epigenetically regulated phenotype variance in mammals.

The promise of epigenomic therapeutics in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is often viewed to arise primarily by genetic alterations. However, today we know that many aspects of the cancer phenotype require a crosstalk among these genetic alterations with epigenetic changes. Indeed, aberrant gene expression patterns, driven by epigenetics are fixed by altered signaling from mutated oncogenes and tumor suppressors to define the PDAC phenotype. This conceptual framework may have significant mechanistic value and could offer novel possibilities for treating patients affected with PDAC. In fact, extensive investigations are leading to the development of small molecule drugs that reversibly modify the epigenome. These new ‘epigenetic therapeutics’ discussed herein are promising to fuel a new era of studies, by providing the medical community with new tools to treat this dismal disease.

Epigenetic Modifications in Essential Hypertension

Essential hypertension (EH) is a complex, polygenic condition with no single causative agent. Despite advances in our understanding of the pathophysiology of EH, hypertension remains one of the world’s leading public health problems. Furthermore, there is increasing evidence that epigenetic modifications are as important as genetic predisposition in the development of EH. Indeed, a complex and interactive genetic and environmental system exists to determine an individual’s risk of EH. Epigenetics refers to all heritable changes to the regulation of gene expression as well as chromatin remodelling, without involvement of nucleotide sequence changes. Epigenetic modification is recognized as an essential process in biology, but is now being investigated for its role in the development of specific pathologic conditions, including EH. Epigenetic research will provide insights into the pathogenesis of blood pressure regulation that cannot be explained by classic Mendelian inheritance. This review concentrates on epigenetic modifications to DNA structure, including the influence of non-coding RNAs on hypertension development.

Epigenetic regulation of mitochondrial function in neurodegenerative disease: New insights from advances in genomic technologies

The field of mitochondrial epigenetics has received increased attention in recent years and changes in mitochondrial DNA (mtDNA) methylation has been implicated in a number of diseases, including neurodegenerative diseases such as amyotrophic lateral sclerosis. However, current publications have been limited by the use of global or targeted methods of measuring DNA methylation. In this review, we discuss current findings in mitochondrial epigenetics as well as its potential role as a regulator of mitochondria within the brain. Finally, we summarize the current technologies best suited to capturing mtDNA methylation, and how a move towards whole epigenome sequencing of mtDNA may help to advance our current understanding of the field.

DNA methylation analysis in constitutional disorders: Clinical implications of the epigenome

Genomic, chromosomal, and gene-specific changes in the DNA sequence underpin both phenotypic variations in populations as well as disease associations, and the application of genomic technologies for the identification of constitutional (inherited) or somatic (acquired) alterations in DNA sequence forms a cornerstone of clinical and molecular genetics. In addition to the disruption of primary DNA sequence, the modulation of DNA function by epigenetic phenomena, in particular by DNA methylation, has long been known to play a role in the regulation of gene expression and consequent pathogenesis. However, these epigenetic factors have been identified only in a handful of pediatric conditions, including imprinting disorders. Technological advances in the past decade that have revolutionized clinical genomics are now rapidly being applied to the emerging discipline of clinical epigenomics. Here, we present an overview of epigenetic mechanisms with a focus on DNA modifications, including the molecular mechanisms of DNA methylation and subtypes of DNA modifications, and we describe the classic and emerging genomic technologies that are being applied to this study. This review focuses primarily on constitutional epigenomic conditions associated with a spectrum of developmental and intellectual disabilities. Epigenomic disorders are discussed in the context of global genomic disorders, imprinting disorders, and single gene disorders. We include a section focused on integration of genetic and epigenetic mechanisms together with their effect on clinical phenotypes. Finally, we summarize emerging epigenomic technologies and their impact on diagnostic aspects of constitutional genetic and epigenetic disorders.