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: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.

Project description:Approximately 25% of all head and neck cancers (HNC), and up to 60% of oropharyngeal cancers (OPC) are associated with human papillomavirus (HPV), predominantly HPV16. HPV-associated OPC have better prognosis and a more favorable response to therapy as compared to HPV-negative tumors. Viral oncoproteins are capable of transforming primary human keratinocytes from either genital or oral epithelia in vitro and most likely play the same role in vivo, by disrupting cell-cycle regulatory pathways leading to a genetic progression to ano-genital cancer and OPC. However, the precise mechanisms by which HPV mediates malignant transformation of keratinocytes in the upper digestive tract epithelia are not entirely clear. HPV E7-mediated inactivation of pRb results in overexpression of p16INK4A, which is commonly used as a clinical surrogate marker for HPV positivity/activity. However, high p16INK4A alone has insufficient sensitivity and specificity as a biomarker of HPV positivity in different mucosal sub-sites of HNC. Therefore, increasing emphasis is being placed on the assessment of viral load and E7 oncogene expression, resulting in further classification of HPV positive OPC as HPV-active and HPV-inactive. Differences in risk factors, age of presentation, clinical behavior and gene expression profiles indicate that HPV-positive and HPV-negative tumors develop via different molecular mechanisms and are biologically distinct. According to some reports, the rate of HPV-associated tumors is much lower in AA patients as compared to EA patients in United States. This study aimed to compare the gene expression profiles of HPV-active, -inactive and -negative OPCs from european american patients, and determine their biological differences. ANALYSIS 3: Three-condition, one-color experiment: HPV-active, HPV-inactive and HPV-negative oropharyngeal tumor samples from european american patients. Biological replicates: 8 HPV Negative Tumors. 4 HPV Inactive Tumors. 11 HPV Active Tumors.

Project description:Transcription factors (TFs) bind to thousands of DNA sequences in mammalian genomes, but most of these binding events appear to have no direct effect on gene expression. It is unclear why only a subset of transcription factor bound sites are actively involved in transcriptional regulation, nor are the key genomic features known that discriminate between active and inactive TF binding events. Recent studies have identified promoter-distal RNA polymerase II (RNAP2) binding at enhancer elements, suggesting that these interactions may serve as a potential marker for active regulatory sequences. Despite these correlative analyses, a thorough functional validation of these genomic co-occupancies is still lacking. To characterize systematically the gene regulatory activity of DNA sequences underlying promoter-distal TF binding events that co-occur with RNAP2 and TF sites devoid of RNAP2 occupancy using a functional assay, we performed cis-regulatory element sequencing (CRE-seq) reporter assays. We tested more than 1,000 promoter-distal CCAAT/enhancer-binding protein beta (CEBPB) bound sites in two human cell types, HepG2 and K562. We found that CEBPB bound sites that co-occur with RNAP2 were more likely to exhibit enhancer activity in our reporter assay and these active sequences display significantly stronger RNAP2 read enrichment and local enhancer RNA (eRNA) activity compared to inactive sites. CEBPB-bound sites further maintained substantial cell type specificity, indicating that DNA sequence information at such sites can accurately convey cell type-specific regulatory information, supporting a strong role for local DNA sequence in distinguishing active from inactive TF-bound loci. By comparing our CRE-seq results to a comprehensive set of over 1,000 genome annotations, we identified a variety of genomic features that are strong predictors of regulatory element activity as well as cell type-specific activity. Collectively, our functional assay results indicate that RNAP2 occupancy can be used as a key genomic marker that can discriminate active versus inactive transcription factor bound sites.

Dataset Information

Expression data from active human umbilical cord mesenchymal stem cell (active HUMSC) and inactive human umbilical cord mesenchymal stem cell (inactive HUMSC)

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