Project description:X chromosome inactivation (XCI) is a dosage compensation mechanism that silences the majority of genes on one X chromosome in each female cell. In order to characterize epigenetic changes that accompany this process, we measured DNA methylation levels in both 45,X Turner syndrome patients, who carry a single active X chromosome (Xa) and normal 46,XX females, who carry one Xa and one inactive X (Xi). Methylated DNA was immunoprecipitated and hybridized to tiling oligonucleotide arrays, generating epigenetic profiles of active and inactive X chromosomes. We observed that XCI is accompanied by changes in DNA methylation specifically at CpG islands. While the majority of CpG islands show increased methylation levels on the Xi, XCI results in reduced methylation at ~20% of CpG islands. Both intra- and inter-genic CpG islands are epigenetically modified, with the biggest increase in methylation occuring at the promoters of genes silenced by XCI. In contrast, genes escaping XCI have low levels of promoter methylation, while genes that undergo polymorphic silencing show intermediate increases in methylation proportionate to their frequency of inactivation. Thus promoter methylation and susceptibility to XCI are correlated. We observed a global correlation between CpG island methylation and the evolutionary age of different X chromosome strata, and that genes escaping XCI show increased methylation within gene bodies. We utilized our epigenetic map to predict both novel genes escaping XCI, and to identify sequence features that may contribute to the XCI process. Finally, as our study included Turner syndrome patients with single X chromosomes of both maternal and paternal origin we searched for parent-of-origin specific methylation differences, but found no evidence to support imprinting on the human X chromosome. Our study provides the first epigenetic profile of active and inactive X chromosomes, giving novel insights into the phenomenon of dosage compensation. Methylated DNA was enriched by immunoprecipitation using antibodies against 5-methylcytosine. meDIP and input DNA was labeled with cy5 and cy3 respectively and hybridized to Nimblegen arrays comprising 2.1 million 50-85mers covering human chromosomes 20, 21, 22, X and Y at a mean density of ~1 probe per 100bp. Resulting log2 fluorescence ratios correspond to methylation levels. Seven patients with Turner syndrome (45,X karyotype), and three normal females (46,XX karyotype) were analyzed. Of the Turner syndrome cases, four had a maternally-derived X, and three had a paternally-derived X chromosome.

Project description:Graves’ ophthalmopathy (GO) is an extrathyroidal complication of Graves’ hyperthyroidism. Orbital fibroblast, an important cell in the pathogenesis of GO, is responsible for GO characteristics during active and inactive stages; however, information on the extensive profiles and the mechanistic regulations behind orbital fibroblast phenotypes are currently limited. The aim of this study was to compare the proteome profile of orbital fibroblasts isolated from inactive GO, active GO and healthy control. The proteome profile was further integrated with global DNA methylation data to identify this epigenetics regulation involved in the pathogenesis of GO. Methods Orbital fibroblasts culture isolated from five inactive GO, four active GO and five controls were cultured for total protein and DNA extraction. The labelled and fractionated proteins were analyzed with a liquid chromatography tandem-mass spectrometer (LC-MS/MS). On the other hand, the bisulphite-treated DNA was measured with the Illumina Infinium Human Methylation 450K beadchip. Proteome and methylation data were validated by real-time quantitative (RQ)-PCR. Network, pathway and functional analysis were performed by Ingenuity (Qiagen). Results Orbital fibroblasts from active GO displayed overexpression of proteins typically involved with inflammation, cellular proliferation, hyaluronan synthesis and adipogenesis, while several proteins linked to extracellular matrix (ECM) biology and fibrotic disease were overexpressed in orbital fibroblasts from inactive GO. The DNA methylation patterns were similar in healthy control and inactive GO orbital fibroblasts which were distinct from active GO orbital fibroblasts. In orbital fibroblasts from active GO hypermethylated genes link to inflammation while those genes hypomethylated are involved in adipogenesis and autoimmune-related genes. For the network analysis, overlapped between hypermethylated and hypomethylated genes were observed including NF-B, ERK1/2, Alp, RNA polymerase II, Akt and IFNα. In addition, NF-κB, Akt and IFNα were also identified in networks from the differentially expressed proteins. In general, poor correlation between protein expression, DNA methylation and mRNA expression in our study was observed.

Project description:X chromosome inactivation (XCI) is a dosage compensation mechanism that silences the majority of genes on one X chromosome in each female cell. In order to characterize epigenetic changes that accompany this process, we measured DNA methylation levels in both 45,X Turner syndrome patients, who carry a single active X chromosome (Xa) and normal 46,XX females, who carry one Xa and one inactive X (Xi). Methylated DNA was immunoprecipitated and hybridized to tiling oligonucleotide arrays, generating epigenetic profiles of active and inactive X chromosomes. We observed that XCI is accompanied by changes in DNA methylation specifically at CpG islands. While the majority of CpG islands show increased methylation levels on the Xi, XCI results in reduced methylation at ~20% of CpG islands. Both intra- and inter-genic CpG islands are epigenetically modified, with the biggest increase in methylation occuring at the promoters of genes silenced by XCI. In contrast, genes escaping XCI have low levels of promoter methylation, while genes that undergo polymorphic silencing show intermediate increases in methylation proportionate to their frequency of inactivation. Thus promoter methylation and susceptibility to XCI are correlated. We observed a global correlation between CpG island methylation and the evolutionary age of different X chromosome strata, and that genes escaping XCI show increased methylation within gene bodies. We utilized our epigenetic map to predict both novel genes escaping XCI, and to identify sequence features that may contribute to the XCI process. Finally, as our study included Turner syndrome patients with single X chromosomes of both maternal and paternal origin we searched for parent-of-origin specific methylation differences, but found no evidence to support imprinting on the human X chromosome. Our study provides the first epigenetic profile of active and inactive X chromosomes, giving novel insights into the phenomenon of dosage compensation.

Dataset Information

Homo sapiens

Similar Datasets

OmicsDI is part of the ELIXIR infrastructure