Whole-genome DNA Methylation Profiles Research Articles

Genome-wide DNA methylation profile in mungbean

DNA methylation on cytosine residues is known to affect gene expression and is potentially responsible for the phenotypic variations among different crop cultivars. Here, we present the whole-genome DNA methylation profiles and assess the potential effects of single nucleotide polymorphisms (SNPs) for two mungbean cultivars, Sunhwanogdu (VC1973A) and Kyunggijaerae#5 (V2984). By measuring the DNA methylation levels in leaf tissue with the bisulfite sequencing (BSseq) approach, we show both the frequencies of the various types of DNA methylation and the distribution of weighted gene methylation levels. SNPs that cause nucleotide changes from/to CHH – where C is cytosine and H is any other nucleotide – were found to affect DNA methylation status in VC1973A and V2984. In order to better understand the correlation between gene expression and DNA methylation levels, we surveyed gene expression in leaf tissues of VC1973A and V2984 using RNAseq. Transcript expressions of paralogous genes were controlled by DNA methylation within the VC1973A genome. Moreover, genes that were differentially expressed between the two cultivars showed distinct DNA methylation patterns. Our mungbean genome-wide methylation profiles will be valuable resources for understanding the phenotypic variations between different cultivars, as well as for molecular breeding.

Whole-Genome DNA Methylation Analysis of Peripheral Blood Mononuclear Cells in Multiple Sclerosis Patients with Different Disease Courses

Multiple sclerosis (MS) is a severe neurodegenerative disease of polygenic etiology affecting the central nervous system. In addition to genetic factors, epigenetic mechanisms, primarily DNA methylation, which regulate gene expression, play an important role in MS development and progression. In this study, we have performed the first whole-genome DNA methylation profiling of peripheral blood mononuclear cells in relapsing-remitting MS (RRMS) and primary-progressive MS (PPMS) patients and compared them to those of healthy individuals in order to identify the differentially methylated CpG-sites (DMSs) associated with these common clinical disease courses. In addition, we have performed a pairwise comparison of DNA methylation profiles in RRMS and PPMS patients. All three pairwise comparisons showed significant differences in methylation profiles. Hierarchical clustering of the identified DMS methylation levels and principal component analysis for data visualization demonstrated a clearly defined aggregation of DNA samples of the compared groups into separate clusters. Compared with the control, more DMSs were identified in PPMS patients than in RRMS patients (67 and 30, respectively). More than half of DMSs are located in genes, exceeding the expected number for random distribution of DMSs between probes. RRMS patients mostly have hypomethylated DMSs, while in PPMS patients DMSs are mostly hypermethylated. CpG-islands and CpG-shores contain 60% of DMSs, identified by pairwise comparison of RRMS and control groups, and 79% of those identified by pairwise comparison of PPMS and control groups. Pairwise comparison of patients with two clinical MS courses revealed 51 DMSs, 82% of which are hypermethylated in PPMS. Overall, it was demonstrated that there are more changes in the DNA methylation profiles in PPMS than in RRMS. The data confirm the role of DNA methylation in MS development. We have shown, for the first time, that DNA methylation as an epigenetic mechanism is involved in the formation of two distinct clinical courses of MS: namely, RRMS and PPMS.

Whole-genome DNA methylation and hydroxymethylation profiling for HBV-related hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a common solid tumor worldwide with a poor prognosis. Accumulating evidence has implicated important regulatory roles of epigenetic modifications in the occurrence and progression of HCC. In the present study, we analyzed 5-methylcytosine (5-mC) and 5-hydroxymethylcytosine (5-hmC) levels in the tumor tissues and paired adjacent peritumor tissues (APTs) from four individual HCC patients using a (hydroxy)methylated DNA immunoprecipitation approach combined with deep sequencing [(h)MeDIP-Seq]. Bioinformatics analysis revealed that the 5-mC levels in the promoter regions of 2796 genes and the 5-hmC levels in 507 genes differed significantly between HCC tissues and APTs. These differential genes were grouped into various clusters and pathways and found to be particularly enriched in the 'metabolic pathways' that include 'Glycolysis/gluconeogenesis', 'Oxidative phosphorylation' and 'Citrate cycle (TCA cycle)', implicating a potential role of metabolic alterations in HCC. Furthermore, 144 genes had both 5-mC and 5-hmC changes in HCC patients, and 10 of them (PCNA, MDM2, STAG1, E2F4, FGF4, FGF19, RHOBTB2, UBE2QL1, DCN and HSP90AA1) were enriched and interconnected in five pathways including the 'Cell cycle', 'Pathway in cancer', 'Ubiquitin mediated proteolysis', 'Melanoma' and 'Prostate cancer' pathways. The genome-wide mapping of 5-mC and 5-hmC in HCC tissues and APTs indicated that both 5-mC and 5-hmC epigenetic modifications play important roles in the regulation of HCC, and there may be some interconnections between them. Taken together, in the present study we conducted the first genome-wide mapping of DNA methylation combined with hydroxymethylation in HBV-related HCC and provided a series of potential novel epigenetic biomarkers for HCC.

Genome-wide DNA methylation analyses in lung adenocarcinomas: Association with EGFR, KRAS and TP53 mutation status, gene expression and prognosis

BackgroundDNA methylation alterations are early events in tumorigenesis and important in the regulation of gene expression in cancer cells. Lung cancer patients have in general a poor prognosis, and a deeper insight into the epigenetic landscape in lung adenocarcinoma tumors and its prognostic implications is needed. ResultsWe determined whole-genome DNA methylation profiles of 164 fresh frozen lung adenocarcinoma samples and 19 samples of matched normal lung tissue using the Illumina Infinium 450K array. A large number of differentially methylated CpGs in lung adenocarcinoma tissue were identified, and specific methylation profiles were observed in tumors with mutations in the EGFR-, KRAS- or TP53 genes and according to the patients' smoking status. The methylation levels were correlated with gene expression and both positive and negative correlations were seen. Methylation profiles of the tumor samples identified subtypes of tumors with distinct prognosis, including one subtype enriched for TP53 mutant tumors. A prognostic index based on the methylation levels of 33 CpGs was established, and was significantly associated with prognosis in the univariate analysis using an independent cohort of lung adenocarcinoma patients from The Cancer Genome Atlas project. CpGs in the HOX B and HOX C gene clusters were represented in the prognostic signature. ConclusionsMethylation differences mirror biologically important features in the etiology of lung adenocarcinomas and influence prognosis.

Investigating DNA methylation dynamics and safety of human embryonic stem cell differentiation toward striatal neurons.

The potential use of human embryonic stem cells (hESCs) in cell-based therapies points out the critical importance of epigenomic evaluation for cell-based therapies. Specifically, DNA methylation appears to be a crucial player in establishing cell fate commitment and lineage choices. In this study, we report the global changes observed on the CpG islands distributed in promoters, gene bodies, and intergenic regions and the major biochemical pathways and genes involved in methylation changes as H9-hESCs turn into a neuronal culture containing medium-sized spiny striatal neurons (MSNs). Using an ontogeny-recapitulating protocol of striatal neuron differentiation, we analyzed DNA methylation profiles during the conversion from pluripotency to neuropotency up to the acquisition of a mature neuronal phenotype. H9-hESCs changed the methylation pattern both through de novo methylation and hypomethylation of specific gene promoters. Bioinformatic analysis allowed us to identify a panel of striatal-associated genes, which were regulated by DNA methylation and differentially expressed during striatal commitment. Importantly, DNA methylation analysis revealed that H9-hESCs did not acquire methylation-based oncogenic properties after differentiation. Indeed, hypermethylation of cancer-associated genes that characterize transformed cells, such as Polycomb repressive complex-associated genes, was not detected in the neuronal cultures. However, the oncosuppressor gene, BCL2L11, became hypermethylated in H9-hESC-derived mature neurons. Whole-genome DNA methylation profiling could become a technological platform to predict the differentiative potential of hESC-derived cultures and establish further biosafety assessment quality control tools of the cell-based products.

Whole-genome DNA methylation profiling with nucleotide resolution.

In many eukaryotic organisms, methylation at the fifth carbon of cytosine (5mC) is a stable epigenetic mark crucial for many biological processes, including cell differentiation, X-chromosome inactivation, transposon silencing, and genomic imprinting. DNA methylation can be stably inherited to the subsequent generation. It can also change dynamically in response to developmental cues or environmental stimuli, and is an important regulator for developmental switch and cell fate determination. Consequently, many human diseases are associated with aberrant DNA methylation. Gene-specific methylation analysis by sequencing of bisulfite-treated genomic DNA has been instrumental in understanding how DNA methylation affects gene transcription. In recent years, techniques have been developed for genome-wide 5mC detection, and complete methylome at single base resolution has been reported for several organisms, providing unprecedented details on the dynamic nature of DNA methylation during development. With the advance in high-throughput sequencing and the availability of genome sequences, mapping the methylome for species with complex genomes has become increasingly feasible.

Abstract IA05: Targeting the oxidative stress pathway in rhabdomyosarcoma

Abstract Rhabdomyosarcoma is a soft-tissue sarcoma with molecular and cellular features of developing skeletal muscle. Histologically, there are two major subtypes of rhabdomyosarcoma, embryonal and alveolar, which have distinct clinical, molecular, and genetic features. Patients with resected localized disease are highly curable, but patients with recurrent, metastatic or large unresectable tumors have a poor clinical outcome. In this study, we performed whole-genome sequencing, exome sequencing, RNA-sequencing and DNA methylation profiling of embryonal and alveolar rhabdomyosarcomas. The embryonal tumors had more structural and copy number variations than did alveolar tumors and those lesions result from the accumulation of chromosomal lesions over time. Mutations in the RAS/NF1 pathway were significantly associated with intermediate- and high-risk embryonal rhabdomyosarcoma. In contrast, alveolar rhabdomyosarcoma had fewer genetic lesions overall and there were no known cancer consensus genes that were recurrently mutated other than the PAX3/7-FOXO1translocation that is a hallmark of alveolar rhabdomyosarcoma. DNA methylation profiling and RNA-seq analysis showed that embryonal and alveolar rhabdomyosarcomas are distinct and the alveolar tumors more closely resemble normal myoblasts and myotubes. To identify novel therapeutics for embryonal rhabdomyosarcomas, we developed and characterized 6 orthotopic xenografts of tumors in our discovery cohort. High throughput screening of primary cultures derived from those xenografts identified oxidative stress as a pathway of therapeutic relevance for embryonal rhabdomyosarcoma. Citation Format: Michael A. Dyer. Targeting the oxidative stress pathway in rhabdomyosarcoma. [abstract]. In: Proceedings of the AACR Special Conference on Pediatric Cancer at the Crossroads: Translating Discovery into Improved Outcomes; Nov 3-6, 2013; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2013;74(20 Suppl):Abstract nr IA05.

Genome-wide DNA methylation profiling reveals parity-associated hypermethylation of FOXA1.

Early pregnancy in women by the age of 20 is known to have a profound effect on reduction of lifelong breast cancer risk as compared to their nulliparous counterparts. Additional pregnancies further enhance the protection against breast cancer development. Nationwide trend of delayed pregnancy may contribute to the recently reported increase in the incidence of advanced breast cancer among young women in this country. The underlying mechanism for the parity-associated reduction of breast cancer risk is not clearly understood. The purpose of the current study is to use whole-genome DNA methylation profiling to explore a potential association between parity and epigenetic changes in breast tissue from women with early parity and nulliparity. Breast tissue was collected from age-matched cancer-free women with early parity (age < 20; n = 15) or nulliparity (n = 13). The methyl-CpG binding domain-based capture-sequencing technology was used for whole-genome DNA methylation profiling. Potential parity-associated hypermethylated genes were further verified by locus-specific pyrosequencing, using an expanded cohort of parous (n = 19) and nulliparous (n = 16) women that included the initial samples used in the global analysis. Our study identified six genes that are hypermethylated in the parous group (P < 0.05). Pyrosequencing confirmed parity-associated hypermethylation at multiple CpG islands of the FOXA1 gene, which encodes a pioneer factor that facilitates chromatin binding of estrogen receptor α. Our work identifies several potential methylation biomarkers for parity-associated breast cancer risk assessment. In addition, the results are consistent with the notion that parity-associated epigenetic silencing of FOXA1 contributes to long-term attenuation of the estrogenic impact on breast cancer development.

MethylomeDB: a database of DNA methylation profiles of the brain

MethylomeDB (http://epigenomics.columbia.edu/methylomedb/index.html) is a new database containing genome-wide brain DNA methylation profiles. DNA methylation is an important epigenetic mark in the mammalian brain. In human studies, aberrant DNA methylation alterations have been associated with various neurodevelopmental and neuropsychiatric disorders such as schizophrenia, and depression. In this database, we present methylation profiles of carefully selected non-psychiatric control, schizophrenia, and depression samples. We also include data on one mouse forebrain sample specimen to allow for cross-species comparisons. In addition to our DNA methylation data generated in-house, we have and will continue to include published DNA methylation data from other research groups with the focus on brain development and function. Users can view the methylation data at single-CpG resolution with the option of wiggle and microarray formats. They can also download methylation data for individual samples. MethylomeDB offers an important resource for research into brain function and behavior. It provides the first source of comprehensive brain methylome data, encompassing whole-genome DNA methylation profiles of human and mouse brain specimens that facilitate cross-species comparative epigenomic investigations, as well as investigations of schizophrenia and depression methylomes.

Whole-genome DNA methylation profiling using MethylCap-seq

MethylCap-seq is a robust procedure for genome-wide profiling of DNA methylation. The approach consists of the capture of methylated DNA using the MBD domain of MeCP2, and subsequent next-generation sequencing of eluted DNA. Elution of the captured methylated DNA is done in steps using a salt gradient, which stratifies the genome into fractions with different CpG density. The enrichment reached within the individual eluates allows for cost-effective deep sequence coverage. The profiles together yield a detailed genome-wide map of methylated regions and readily allows detection of DNA methylation in known and novel regions. Here, we describe principles and details of the MethylCap-seq procedure using different sources of starting material.

Genome-wide analysis of aberrant methylation in human breast cancer cells using methyl-DNA immunoprecipitation combined with high-throughput sequencing

BackgroundCancer cells undergo massive alterations to their DNA methylation patterns that result in aberrant gene expression and malignant phenotypes. However, the mechanisms that underlie methylome changes are not well understood nor is the genomic distribution of DNA methylation changes well characterized.ResultsHere, we performed methylated DNA immunoprecipitation combined with high-throughput sequencing (MeDIP-seq) to obtain whole-genome DNA methylation profiles for eight human breast cancer cell (BCC) lines and for normal human mammary epithelial cells (HMEC). The MeDIP-seq analysis generated non-biased DNA methylation maps by covering almost the entire genome with sufficient depth and resolution. The most prominent feature of the BCC lines compared to HMEC was a massively reduced methylation level particularly in CpG-poor regions. While hypomethylation did not appear to be associated with particular genomic features, hypermethylation preferentially occurred at CpG-rich gene-related regions independently of the distance from transcription start sites. We also investigated methylome alterations during epithelial-to-mesenchymal transition (EMT) in MCF7 cells. EMT induction was associated with specific alterations to the methylation patterns of gene-related CpG-rich regions, although overall methylation levels were not significantly altered. Moreover, approximately 40% of the epithelial cell-specific methylation patterns in gene-related regions were altered to those typical of mesenchymal cells, suggesting a cell-type specific regulation of DNA methylation.ConclusionsThis study provides the most comprehensive analysis to date of the methylome of human mammary cell lines and has produced novel insights into the mechanisms of methylome alteration during tumorigenesis and the interdependence between DNA methylome alterations and morphological changes.