Combined chromatin immunoprecipitation and bisulfite methylation sequencing analysis

Temporally discordant chromatin accessibility and DNA demethylation define short and long-term enhancer regulation during cell fate specification

Epigenetic mechanisms govern the transcriptional activity of lineage-specifying enhancers; but recent work challenges the dogma that joint chromatin accessibility and DNA demethylation are prerequisites for transcription. To understand this paradox, we established a highly-resolved timeline of DNA demethylation, chromatin accessibility, and transcription factor occupancy during neural progenitor cell differentiation. We show thousands of enhancers undergo rapid, transient accessibility changes associated with distinct periods of transcription factor expression. However, most DNA methylation changes are unidirectional and delayed relative to chromatin dynamics, creating transiently discordant epigenetic states. Genome-wide detection of 5-hydroxymethylcytosine further revealed active demethylation begins ahead of chromatin and transcription factor activity, while enhancer hypomethylation persists long after these activities have dissipated. We demonstrate that these timepoint specific methylation states predict past, present and future chromatin accessibility using machine learning models. Thus, chromatin and DNA methylation collaborate on different timescales to mediate short and long-term enhancer regulation during cell fate specification.

Genome-wide methylation analysis of treatment resistant schizophrenia

Various studies have investigated the relationship between genetic polymorphisms of antipsychotic drug-metabolizing agents and drug response. DNA methylation is a form of epigenetic modification that regulates gene expression. Few studies have analyzed the relationship between genome-wide methylation patterns and treatment resistance schizophrenia. The primary aim of this pilot study is to investigate the association between treatment resistance status and genome-wide DNA methylation in schizophrenia patients. Treatment resistance status was determined for 109 patients with schizophrenia. Treatment resistance was the primary outcome variable in a model, including methylation status of white blood cells using the Illumina 450 array. The genome-wide DNA methylation levels in 109 Schizophrenia subjects did not show that DNA methylation sties were associated with resistance status. From our study, it is evident the importance of continuing to investigate the relationship between DNA methylation and antipsychotic response to personalize treatment in schizophrenia. Future studies require larger prescription databases to build on the results presented in this pilot study.

Genome-wide methylation analysis of early-onset schizophrenia

OBJECTIVE

Schizophrenia (SCZ) is a debilitating disease with a complex genetic cause in which age at onset may reflect genetic vulnerability. Though there has been some association between genetic polymorphisms and age of onset, there has been little exploration of the role of epigenetic processes. We sought to explore the influence of DNA methylation, a key epigenetic mechanism, and its association with the age of onset of illness.

METHODS

One hundred thirty-eight participants aged 18-75 years and previously diagnosed with SCZ spectrum disorders by the Structured Clinical Interview for the Diagnostic and Statistical Manual of Mental Disorders (SCID DSM-5) were recruited. Venous blood was collected and genome-wide DNA methylation was quantified using the Illumina Infinium HumanMethylation450 BeadChip array. Individual CpG sites and regions of differential methylation were explored by the age of onset; covariates included age, sex, as well as white blood cell composition.

RESULTS

Binary grouping (early vs. late onset) revealed four intergenic CpG sites on chromosome 2 that were above the expected P-value threshold, with hypermethylation of the CpG site cg10392614 most strongly associated with early-onset SCZ. The four most strongly associated CpG sites, including cg 10392614, were intergenic. Continuous analysis revealed the top CpG site to be cg11723066 , which is linked to the JAM3 gene, with hypomethylation associated with earlier onset; however, results were below the expected P-value threshold.

CONCLUSION

Studies on DNA methylation in the first-episode psychosis population may help further our understanding of the role of epigenetics in the age of onset of SCZ.

Expanding studies of chromosome structure and function in the era of T2T genomics

The recent accomplishment of a truly complete human genome has afforded a new view of chromosome structure and function that was limited 30 years ago. Here, we discuss the expansion of knowledge from the early cytological studies of the genome to the current high-resolution genomic, epigenetic and functional maps that have been achieved by recent technology and computational advances. These studies have revealed unexpected complexities of genome organization and function and uncovered new views of fundamental chromosomal elements. Comprehensive genomic maps will enable accurate diagnosis of human diseases caused by altered chromosome structure and function, facilitate development of chromosome-based therapies and shape the future of preventative medicine and healthcare.

Genomics Armed With Diversity Leads the Way in Brassica Improvement in a Changing Global Environment

Meeting the needs of a growing world population in the face of imminent climate change is a challenge; breeding of vegetable and oilseed Brassica crops is part of the race in meeting these demands. Available genetic diversity constituting the foundation of breeding is essential in plant improvement. Elite varieties, land races, and crop wild species are important resources of useful variation and are available from existing genepools or genebanks. Conservation of diversity in genepools, genebanks, and even the wild is crucial in preventing the loss of variation for future breeding efforts. In addition, the identification of suitable parental lines and alleles is critical in ensuring the development of resilient Brassica crops. During the past two decades, an increasing number of high-quality nuclear and organellar Brassica genomes have been assembled. Whole-genome re-sequencing and the development of pan-genomes are overcoming the limitations of the single reference genome and provide the basis for further exploration. Genomic and complementary omic tools such as microarrays, transcriptomics, epigenetics, and reverse genetics facilitate the study of crop evolution, breeding histories, and the discovery of loci associated with highly sought-after agronomic traits. Furthermore, in genomic selection, predicted breeding values based on phenotype and genome-wide marker scores allow the preselection of promising genotypes, enhancing genetic gains and substantially quickening the breeding cycle. It is clear that genomics, armed with diversity, is set to lead the way in Brassica improvement; however, a multidisciplinary plant breeding approach that includes phenotype = genotype × environment × management interaction will ultimately ensure the selection of resilient Brassica varieties ready for climate change.

Modern epigenetics methods in biological research

The definition of epigenetics refers that molecular modifications on DNA that can regulate gene activity are independent of DNA sequence and mitotically stable. Notably, epigenetics studies have grown exponentially in the past few years. Recent progresses that lead to exciting discoveries and groundbreaking nature of this area demand thorough methodologies and advanced technologies to move epigenetics to the forefront of molecular biology. The most recognized epigenetic regulations are DNA methylation, histone modifications, and non-coding RNAs (ncRNAs). This review will discuss the modern techniques that are available to detect locus-specific and genome-wide changes for all epigenetic codes. Furthermore, updated analysis of technologies, newly developed methods, recent breakthroughs and bioinformatics pipelines in epigenetic analysis will be presented. These methods, as well as many others presented in this specific issue, provide comprehensive guidelines in the area of epigenetics that facilitate further developments in this promising and rapidly developing field.

ATAC-Me Captures Prolonged DNA Methylation of Dynamic Chromatin Accessibility Loci during Cell Fate Transitions

DNA methylation of enhancers is dynamic, cell-type specific, and vital for cell fate progression. However, current models inadequately define its role within the hierarchy of gene regulation. Analysis of independent datasets shows an unanticipated overlap between DNA methylation and chromatin accessibility at enhancers of steady-state stem cells, suggesting that these two opposing features might exist concurrently. To define their temporal relationship, we developed ATAC-Me, which probes accessibility and methylation from single DNA library preparations. We identified waves of accessibility occurring rapidly across thousands of myeloid enhancers in a monocyte-to-macrophage cell fate model. Prolonged methylation states were observed at a majority of these sites, while transcription of nearby genes tracked closely with accessibility. ATAC-Me uncovers a significant disconnect between chromatin accessibility, DNA methylation status, and gene activity. This unexpected observation highlights the value of ATAC-Me in constructing precise molecular timelines for understanding the role of DNA methylation in gene regulation.

Sequencing in High Definition Drives a Changing Worldview of the Epigenome

Single-molecule sequencing approaches have transformed the study of the human epigenome, accelerating efforts to describe genome function beyond the sequences that encode proteins. The post-genome era has ignited strong interest in the noncoding genome and profiling epigenetic signatures genome-wide have been critical for the identification and characterization of noncoding gene-regulatory sequences in various cellular and developmental contexts. These technologies enable quantification of epigenetic marks through digital assessment of DNA fragments. With the capacity to probe both the DNA sequence and count DNA molecules at once with unparalleled throughput and sensitivity, deep sequencing has been especially transformative to the study of DNA methylation. This review will discuss advances in epigenome profiling with a particular focus on DNA methylation, highlighting how deep sequencing has generated new insights into the role of DNA methylation in gene regulation. Technical aspects of profiling DNA methylation, remaining challenges, and the future of DNA methylation sequencing are also described.

Promoter Methylation Pattern Controls Corticotropin Releasing Hormone Gene Activity in Human Trophoblasts

Placental CRH production increases with advancing pregnancy in women and its course predicts gestational length. We hypothesized that CRH gene expression in the placenta is epigenetically controlled setting gestational trajectories characteristic of normal and pathological pregnancies. Here we determined histone modification and DNA methylation levels and DNA methylation patterns at the CRH promoter in primary trophoblast cultures by chromatin immunoprecipitation combined with clonal bisulfite sequencing and identified the transcriptionally active epialleles that associate with particular histone modifications and transcription factors during syncytialisation and cAMP-stimulation. CRH gene expression increased during syncytial differentiation and cAMP stimulation, which was associated with increased activating and decreased repressive histone modification levels at the promoter. DNA methylation levels remained unchanged. The nine CpGs of the CRH proximal promoter were partially and allele-independently methylated displaying many (>100) epialleles. RNA-polymerase-II (Pol-II) bound only to three particular epialleles in cAMP-stimulated cells, while phospho-cAMP response element-binding protein (pCREB) bound to only one epiallele, which was different from those selected by Pol-II. Binding of TATA-binding protein increased during syncytial differentiation preferentially at epialleles compatible with Pol-II and pCREB binding. Histone-3 acetylation was detected only at epialleles targeted by Pol-II and pCREB, while gene activating histone-4 acetylation and histone-3-lysine-4 trimethylation occurred at CRH epialleles not associated with Pol-II or pCREB. The suppressive histone-3-lysine-27 trimethyl and-lysine-9 trimethyl modifications showed little or no epiallele preference. The epiallele selectivity of activating histone modifications and transcription factor binding demonstrates the epigenetic and functional diversity of the CRH gene in trophoblasts, which is controlled predominantly by the patterns, not the overall extent, of promoter methylation. We propose that conditions impacting on epiallele distribution influence the number of transcriptionally active CRH gene copies in the trophoblast cell population determining the gestational trajectory of placental CRH production in normal and pathological pregnancies.

Advances in the profiling of DNA modifications: cytosine methylation and beyond

Chemical modifications of DNA have been recognized as key epigenetic mechanisms for maintenance of the cellular state and memory. Such DNA modifications include canonical 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxycytosine (5caC). Recent advances in detection and quantification of DNA modifications have enabled epigenetic variation to be connected to phenotypic consequences on an unprecedented scale. These methods may use chemical or enzymatic DNA treatment, may be targeted or non-targeted and may utilize array-based hybridization or sequencing. Key considerations in the choice of assay are cost, minimum sample input requirements, accuracy and throughput. This Review discusses the principles behind recently developed techniques, compares their respective strengths and limitations and provides general guidelines for selecting appropriate methods for specific experimental contexts.

Real-time analysis and selection of methylated DNA by fluorescence-activated single molecule sorting in a nanofluidic channel

Epigenetic modifications, such as DNA and histone methylation, are responsible for regulatory pathways that affect disease. Current epigenetic analyses use bisulfite conversion to identify DNA methylation and chromatin immunoprecipitation to collect molecules bearing a specific histone modification. In this work, we present a proof-of-principle demonstration for a new method using a nanofluidic device that combines real-time detection and automated sorting of individual molecules based on their epigenetic state. This device evaluates the fluorescence from labeled epigenetic modifications to actuate sorting. This technology has demonstrated up to 98% accuracy in molecule sorting and has achieved postsorting sample recovery on femtogram quantities of genetic material. We have applied it to sort methylated DNA molecules using simultaneous, multicolor fluorescence to identify methyl binding domain protein-1 (MBD1) bound to full-duplex DNA. The functionality enabled by this nanofluidic platform now provides a workflow for color-multiplexed detection, sorting, and recovery of single molecules toward subsequent DNA sequencing.

Bisulfite sequencing of chromatin immunoprecipitated DNA (BisChIP-seq) directly informs methylation status of histone-modified DNA

The complex relationship between DNA methylation, chromatin modification, and underlying DNA sequence is often difficult to unravel with existing technologies. Here, we describe a novel technique based on high-throughput sequencing of bisulfite-treated chromatin immunoprecipitated DNA (BisChIP-seq), which can directly interrogate genetic and epigenetic processes that occur in normal and diseased cells. Unlike most previous reports based on correlative techniques, we found using direct bisulfite sequencing of Polycomb H3K27me3-enriched DNA from normal and prostate cancer cells that DNA methylation and H3K27me3-marked histones are not always mutually exclusive, but can co-occur in a genomic region-dependent manner. Notably, in cancer, the co-dependency of marks is largely redistributed with an increase of the dual repressive marks at CpG islands and transcription start sites of silent genes. In contrast, there is a loss of DNA methylation in intergenic H3K27me3-marked regions. Allele-specific methylation status derived from the BisChIP-seq data clearly showed that both methylated and unmethylated alleles can simultaneously be associated with H3K27me3 histones, highlighting that DNA methylation status in these regions is not dependent on Polycomb chromatin status. BisChIP-seq is a novel approach that can be widely applied to directly interrogate the genomic relationship between allele-specific DNA methylation, histone modification, or other important epigenetic regulators.