Unknown,Transcriptomics,Genomics,Proteomics

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DNA Methylation Predictors of Gene Expression in the 1st Trimester Chorionic Villus: Implications for Prenatal Diagnosis

ABSTRACT: Placental gene expression is a finely controlled process, yet little is known about the factors that regulate it, including epigenetic factors such as DNA methylation. In this study, we quantified the effects of DNA methylation on placental gene expression. Using targeted high throughput sequencing, we generated methylation profiles of 3.7 million CpG dinucleotides from 6 karyotypically normal CVS samples and compared these to gene expression data obtained from a publically available database. We found a broad association between methylation and gene expression at both the chromosome and individual gene levels. At the chromosome level, we found alternating domains of high and low methylation. Within each gene, we found distinct methylation patterns at different regulatory genetic elements. For example, the promoters of highly expressed genes were neither highly methylated, nor completely unmethylated. Rather, they had < 50% of the CG dinucleotides in their sequences in the methylated state. In contrast, promoters of unexpressed genes tended to be either highly methylated or fully unmethylated. Similarly, patterns of methylation in exons and introns differed between highly expressed and unexpressed genes. Our data show that the relationship between DNA methylation and gene expression is nuanced: highly expressed and unexpressed genes differ, not only by their extent of methylation, but also by minute changes in the locations of their methylation sites. DNA methylation analysis of placental genes may help predict abnormal placental gene expression and pregnancy complications, making it a possible tool for prenatal diagnosis. DNA from 6 chorionic villus samples from the 1st trimester (from 3 male and 3 female fetuses) as well as 3 maternal blood cell samples was extracted, hybridized to probes in the Agilent SureSelectXT Methyl-Seq Target Enrichment kit, targeting 84Mb of the genome and then bisulfite converted before sequencing.

ORGANISM(S): Homo sapiens

SUBMITTER: Varsha Shridhar

PROVIDER: E-GEOD-58826 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Methylation of DNA at CpG dinucleotides represents one of the most important epigenetic mechanisms involved in the control of gene expression in vertebrate cells. In this report, we conducted high-throughput nucleosome reconstitution experiments on 572 KB of human DNA and 668 KB of mouse DNA that was unmethylated or methylated in order to investigate the effects of this epigenetic modification on the positioning and stability of nucleosomes. The DNA loci from both species contained the genes that encode the serum albumin family, the MYC protein, and the tumor suppressor p53. The results demonstrated that a small subset of nucleosomes positioned by nucleotide sequence was sensitive to methylation where the modification increased the affinity of these sequences for the histone octamer. The features that distinguished these nucleosomes from the bulk of the methylation-insensitive nucleosomes were an increase in the frequency of CpG dinucleotides and a unique rotational orientation of CpGs such that their minor grooves tended to face toward the histones in the nucleosome rather than away. We propose that these features serve to enhance the affinity of methylated DNA for the histone octamer and that this effect could be involved in gene regulatory mechanisms such as silencing. These methylation-sensitive nucleosomes were preferentially associated with exons as compared to introns while unmethylated CpG islands near transcription start sites became enriched in nucleosomes upon methylation. The results of this study suggest that the effects of DNA methylation on nucleosome stability in vitro can recapitulate what has been observed in the cell and provide a direct link between DNA methylation and the structure and function of chromatin. For the human data, there were 3 unmethylated nucleosome replicates, 2 methylated nucleosome replicates, an unmethylated MNase control, and an unmethylated sonicated control. For the mouse data, there were 2 unmethylated nucleosome replicates, 2 methylated nucleosome replicates, an unmethylated MNase control, a methylated MNase control, and an unmethylated sonicated control.

Project description:The activation-induced cytidine deaminase enzyme (AID) is required in germinal center (GC) B cells for somatic hyper-mutation and class switch recombination at the immunoglobulin locus. In GC-B cells, AID is highly expressed, with inherent mutator activity that helps generate antibody diversity. However, AID may also regulate gene expression epigenetically, irrespective of mutator activity, by directly deaminating 5-methylcytosine (5mC) in concert with base excision repair glycosylases to exchange unmethylated cytosine. This pathway promotes gene demethylation, thereby removing epigenetic memory. For example, AID promotes active demethylation of the genome in primordial germ cells. However, the range and mechanism by which AID promotes pluripotency is not known. Different studies have suggested either a requirement or a lack of function for promoting pluripotency in somatic nuclei following fusion with embryonic stem cells (ESC). Here we tested directly whether AID regulates epigenetic memory, by comparing the relative ability of cells lacking AID to reprogram from a differentiated cell type to an induced pluripotent stem cell (iPSC). We show that loss of AID impacts two distinct steps of reprogramming: First, AID-null cells are transiently hyper-responsive to the reprogramming process. Second, although they initiate expression of pluripotency genes, they fail to stabilize the pluripotent state. The genome of AID-null cells remains hypermethylated in reprogramming cells, and hypermethylated genes associated with pluripotency fail to be stably up-regulated. MYC target genes are highly enriched in the set of genes hypermethylated and under-expressed in reprogramming cells lacking AID. Recent studies identified a distinctive late step of reprogramming associated with methylation status. AID appears to regulate this step to stabilize the pluripotent state, removing epigenetic memory to promote expression of secondary pluripotency network genes. Transcriptome sequencing of AID-null tail fibroblasts, wildtype tail fibroblasts, AID-null and wildtype tail fibroblasts reprogrammed for three weeks by ectopic expression of transcription factors Oct4, Sox2, KLf4 and cMyc. Methylation profiling by reduced representation bisulphite seuencing of AID-null tail fibroblasts, wildtype tail fibroblasts, AID-null and wildtype tail fibroblasts reprogrammed for three weeks and AID-null and wildtype clones after three weeks of reprogramming (Picked at two weeks)

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DNA Methylation Predictors of Gene Expression in the 1st Trimester Chorionic Villus: Implications for Prenatal Diagnosis

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