Epigenomes, Volume 1, Issue 3 (December 2017) – 11 articles

Environmental factors are playing a central role in triggering inflammatory responses in the intestine. There is increasing evidence that the development of inflammatory bowel disease (IBD) is deriving from an aberrant immune response to the commensal gut microbiota triggered by various environmental factors in a susceptible host. A vitamin A derivate used in acne therapy (isotretinoin) has been inconsistently associated with the onset of IBD. However, what needs to be considered is the previous treatment of acne patients with antibiotics that are also associated with the development of IBD, thus representing a crucial confounding factor. Here, we studied whether doxycycline (acne therapy), metronidazole (IBD therapy) or isotretinoin are able to induce alterations in DNA methylation and microRNA expression patterns in murine colonic intestinal epithelial cells (IECs). Additionally, we analyzed time-dependent changes in the aforementioned epigenetic mechanisms to study how epigenetic signatures evolve over time. As for changes in DNA methylation, we found isotretinoin to have strong demethylating effects, while antibiotic treatment had only a moderate impact. Isotretinoin-mediated demethylation resolved after a washout phase, not supporting an association between isotretinoin treatment and IBD. Regarding microRNA and mRNA expression, isotretinoin and doxycycline, but not metronidazole, potentially induce long-term changes in microRNA/mRNA expression profiles towards the down-regulation of immune responses. Analysis of time-dependent DNA methylation showed stable marks over a time frame of 4 weeks. Furthermore, novel microRNAs were identified (e.g., microRNA-877-3p), which might be of relevance in IEC development. Full article

Background: Epigenetic epidemiology has proven an important research discipline in the delineation of diseases of complex etiology. The approach, in such studies, is often to use bio-banked clinical material, however, many such samples were collected for purposes other than epigenetic studies and, thus, potentially not processed and stored appropriately. The Danish National Birth Cohort (DNBC) includes more than 100,000 peripheral and umbilical cord blood samples shipped from maternity wards by ordinary mail in EDTA tubes. While this and other similar cohorts hold great promises for DNA methylation studies the potential systematic changes prompted by storage at ambient temperatures have never been assessed on a genome-wide level. Methods and Results: In this study, matched EDTA whole blood samples were stored up to three days at room temperature prior to DNA extraction and methylated DNA immunoprecipitation coupled with deep sequencing (MeDIP-seq). We established that the quality of the MeDIP-seq libraries was high and comparable across samples; and that the methylation profiles did not change systematically during the short-time storage at room temperature. Conclusion: The global DNA methylation profile is stable in whole blood samples stored for up to three days at room temperature in EDTA tubes making genome-wide methylation studies on such material feasible. Full article

Transit amplification (TA), a state of combined, rapid proliferative expansion and differentiation of stem cell-descendants, remains poorly defined at the molecular level. The Polycomb Repressive Complex 1 (PRC1) protein BMI1 has been localized to TA compartments, yet its exact role in TA is unclear. PRC1 proteins control gene expression, cell proliferation and DNA-damage repair. Coordination of such DNA-templated activities during TA is predicted to be crucial to support DNA replication and differentiation-associated transcriptional programming. We here examined whether chondrogenesis provides a relevant biological context for synchronized coordination of these chromatin-based tasks by BMI1. Taking advantage of a prominently featuring TA-phase during chondrogenesis in vitro and in vivo, we here report that TA is completely dependent on intact PRC1 function. BMI1-depleted chondrogenic progenitors rapidly accumulate double strand DNA breaks during DNA replication, present massive non-H3K27me3-directed transcriptional deregulation and fail to undergo chondrogenic TA. Genome-wide accumulation of Topoisomerase 2α and Geminin suggests a model in which PRC1 synchronizes replication and transcription during rapid chondrogenic progenitor expansion. Our combined data reveals for the first time a vital cell-autonomous role for PRC1 during chondrogenesis. We provide evidence that chondrocyte hyper-replication and hypertrophy represent a unique example of programmed senescence in vivo. These findings provide new perspectives on PRC1 function in development and disease. Full article

Polycomb Group (PcG) proteins are best-known for maintaining repressive or active chromatin states that are passed on across multiple cell divisions, and thus sustain long-term memory of gene expression. PcG proteins engage different, partly gene- and/or stage-specific, mechanisms to mediate spatiotemporal gene expression during central nervous system development. In the course of this, PcG proteins bind to various cis-regulatory sequences (e.g., promoters, enhancers or silencers) and coordinate, as well the interactions between distantly separated genomic regions to control chromatin function at different scales ranging from compaction of the linear chromatin to the formation of topological hubs. Recent findings show that PcG proteins are involved in switch-like changes in gene expression states of selected neural genes during the transition from multipotent to differentiating cells, and then to mature neurons. Beyond neurodevelopment, PcG proteins sustain mature neuronal function and viability, and prevent progressive neurodegeneration in mice. In support of this view, neuropathological findings from human neurodegenerative diseases point to altered PcG functions. Overall, improved insight into the multiplicity of PcG functions may advance our understanding of human neurodegenerative diseases and ultimately pave the way to new therapies. Full article

Over the years, farmed birds have been selected on various performance traits mainly through genetic selection. However, many studies have shown that genetics may not be the sole contributor to phenotypic plasticity. Gene expression programs can be influenced by environmentally induced epigenetic changes that may alter the phenotypes of the developing animals. Recently, high-throughput sequencing techniques became sufficiently affordable thanks to technological advances to study whole epigenetic landscapes in model plants and animals. In birds, a growing number of studies recently took advantage of these techniques to gain insights into the epigenetic mechanisms of gene regulation in processes such as immunity or environmental adaptation. Here, we review the current gain of knowledge on the chicken epigenome made possible by recent advances in high-throughput sequencing techniques by focusing on the two most studied epigenetic modifications, DNA methylation and histone post-translational modifications. We discuss and provide insights about designing and performing analyses to further explore avian epigenomes. A better understanding of the molecular mechanisms underlying the epigenetic regulation of gene expression in relation to bird phenotypes may provide new knowledge and markers that should undoubtedly contribute to a sustainable poultry production. Full article

Epigenetic modes of gene regulation are important for physiological conditions and its aberrant changes can lead to disease like cancer. 5-hydroxymethylcytosine (5hmC) is an oxidized form of 5-methylcytosine (5mC) catalyzed by Ten Eleven Translocation (TET) enzymes. 5hmC is considered to be a demethylation intermediate and is emerging as a stable and functional base modification. The global loss of 5hmC level is commonly observed in cancers and tumorigenic germline mutations in IDH, SDH and FH are found to be inhibiting TET activity. Although a global loss of 5hmC is characteristic in cancers, locus-specific 5hmC gain implicates selective gene expression control. The definitive role of 5hmC as a tumor suppressing or promoting modification can be deduced by identifying locus-specific 5hmC modification in different types of cancer. Determining the genes carrying 5hmC modifications and its selective variation will open up new therapeutic targets. This review outlines the role of global and locus-specific changes of 5hmC in cancers and the possible mechanisms underlying such changes. We have described major cellular factors that influence 5hmC levels and highlighted the significance of 5hmC in tumor micro environmental condition like hypoxia. Full article

The enhancer of zeste homolog 2 (EZH2) gene encodes a histone methyltransferase that is a catalytic subunit of the Polycomb repressive complex 2 (PRC2) group of proteins that act to repress gene expression. The EZH2 locus is rarely mutated in solid tumors and there is no comprehensive study of EZH2 single nucleotide variants (SNVs) associated with cancer susceptibility, prognosis and response to therapy. Here, for the first time, we review the functional roles of EZH2 DNA variants and propose a putative etiological role in 10 various solid tumors including: esophageal, hepatocellular, oral, urothelial, colorectal, lung and gastric cancers. In particular, we found that the C allele of the EZH2 variant rs3757441 is associated with increased EZH2 RNA expression and poorer prognosis (advanced stage) in at least two malignancies such as colorectal and hepatocellular carcinoma. This suggests that the C allele may be a functional risk variant in multiple malignant tumors. We therefore propose that the rs3757441 single nucleotide variant (SNV) be genotyped and real-time PCR assays be performed in large cohort studies in order to confirm this preliminary finding that could be useful for clinical practice. Full article

Consolidation of contextual memories after a stressful encounter is essential for the survival of an organism and in allowing a more appropriate response to be elicited should the perceived threat reoccur. Recent evidence has explored the complex role that epigenetic mechanisms play in the formation of such memories, and the underlying signaling pathways are becoming more apparent. The glucocorticoid receptor (GR) has been shown to play a key role in these events having both genomic and non-genomic actions in the brain. GR has been shown to interact with the extracellular signal-regulated kinase mitogen-activated protein kinase (ERK MAPK) signaling pathway which, in concert, drives epigenetic modifications and chromatin remodeling, resulting in gene induction and memory consolidation. Evidence indicates that stressful events can have an effect on the offspring in utero, and that epigenetic marks altered early in life may persist into adulthood. A new and controversial area of research, however, suggests that epigenetic modifications could be inherited through the germline, a concept known as transgenerational epigenetics. This review explores the role that epigenetic processes play in the central nervous system, specifically in the consolidation of stress-induced memories, the concept of transgenerational epigenetic inheritance, and the potential role of epigenetics in revolutionizing the treatment of stress-related disorders through the emerging field of pharmacoepigenetics and personalized medical treatment. Full article

Experimental alteration of DNA methylation is a suitable tool to infer the relationship between phenotypic and epigenetic variation in plants. A detailed analysis of the genome-wide effect of demethylating agents, such as 5-azacytidine (5azaC), and zebularine is only available for the model species Arabidopsis thaliana, which suggests that 5azaC may have a slightly larger effect. In this study, global methylation estimates obtained by high-performance liquid chromatography (HPLC) analyses were conducted to investigate the impact of 5azaC treatment on leaf and root tissue in Erodium cicutarium (Geraniaceae), which is an annual herb native to Mediterranean Europe that is currently naturalized in all continents, sometimes becoming invasive. We used seeds collected from two natural populations in SE Spain. Root tissue of the second generation (F2) greenhouse-grown seedlings had a significantly lower global cytosine methylation content than leaf tissue (13.0 vs. 17.7% of all cytosines). Leaf tissue consistently decreased methylation after treatment, but the response of root tissue varied according to seed provenance, suggesting that genetic background can mediate the response to experimental demethylation. We also found that both leaf number and leaf length were reduced in treated seedlings supporting a consistent phenotypic effect of the treatment regardless of seedling provenance. These findings suggest that, although the consequences of experimental demethylation may be tissue- and background-specific, this method is effective in altering early seedling development, and can thus be useful in ecological epigenetic studies that are aiming to investigate the links between epigenetic and phenotypic variation in non-model plant species. Full article

The gene EHMT1 that encodes the Euchromatic Histone Methyltransferase-1, also known as GLP (G9a-like protein), has been associated with a number of neurodevelopmental and neurodegenerative disorders. GLP is a member of the euchromatic lysine histone methyltransferase family, along with EHMT2 or G9A. As its name implies, Ehmt1/GLP is involved in the addition of methyl groups to histone H3 lysine 9, a generally repressive mark linked to classical epigenetic process such as genomic imprinting, X-inactivation, and heterochromatin formation. However, GLP also plays both a direct and indirect role in regulating DNA-methylation. Here, we discuss what is currently known about the biochemical function of Ehmt1/GLP and its association, via various genetic studies, with brain disorders. Full article

Abstract: Background: Interrogation of DNA methylation profiles hold promise for improved diagnostics, as well as the delineation of the aetiology for common human diseases. However, as the primary tissue of the disease is often inaccessible without complicated and inconvenient interventions, there is an increasing interest in peripheral surrogate tissues. Whereas most work has been conducted on blood, saliva is now becoming recognized as an interesting alternative due to the simple and non-invasive manner of collection allowing for self-sampling. Results: In this study we have evaluated if saliva samples are suitable for DNA methylation studies using methylated DNA immunoprecipitation coupled to next-generation sequencing (MeDIP-seq). This was done by comparing the DNA methylation profile in saliva against the benchmark profile of peripheral blood from three individuals. We show that the output, quality, and depth of paired-end 50 bp sequencing reads are comparable between saliva and peripheral blood and, moreover, that the distribution of reads along genomic regions are similar and follow canonical methylation patterns. Conclusion: In summary, we show that high-quality MeDIP-seq data can be generated using saliva, thus supporting the future use of saliva in the generation of DNA methylation information at annotated genes, non-RefSeq genes, and repetitive elements relevant to human disease. Full article