Project description:A Cartes d'Identite des Tumeurs (CIT) project from the french Ligue Nationale Contre le Cancer (http://cit.ligue-cancer.net: Oligodendroglial tumours (OT) are a heterogeneous group of gliomas. Three molecular subgroups are currently distinguished based on the IDH mutation and the 1p/19q co-deletion. Here we performed an integrated analysis of the transcriptome, genome and methylome of 156 OT. Beyond the 3 well-known molecular classes, our multi-omics classification revealed 3 subgroups within 1p/19q co-deleted tumours, associated with different expression patterns of oligodendroglial progenitor cell (OPC), astrocytic, oligodendrocytic and neuronal lineage genes. The validity of these 3 subgroups was confirmed on public datasets. The OPC-like group was associated with a more aggressive histological and genomic profile and with MYC activation that occurred through various alterations including MYC locus genomic gain, MYC exon 3 hypo-methylation and down-regulation of microRNA-34b/c. In the lower grade glioma TCGA dataset, the OPC-like group was associated with a poorer outcome independently from histological grade. Our study unravels previously unrecognized heterogeneity among 1p/19q co-deleted tumours.
Project description:Several organisms belonging to diverse animal groups have retained Dnmt2 as their only bona fide DNA methyltransferase gene. However, recent studies have shown that Dnmt2 functions as a tRNA methyltransferase, which prompted us to analyze the methylomes of Dnmt2-only organisms at single-base resolution. Using whole-genome bisulfite sequencing we show here that the genomes of Schistosoma mansoni and Drosophila melanogaster lack detectable DNA methylation patterns. Residual unconverted cytosine residues shared many attributes with bisulfite deamination artifacts and were observed at comparable levels in a Dnmt2-deficient fly strain. Furthermore, genetically modified mouse embryonic stem cells that had retained Dnmt2 as their only bona fide DNA methyltransferase gene, did not show any detectable DNA methylation patterns. Our results thus uncover fundamental differences among animal methylomes and suggest that Dnmt2-only organisms lack biologically relevant DNA methylation patterns. Whole methylome analysis of Mus musculus. One sample was analyzed containing DNA from Dnmt1-/-, Dnmt3a-/- and Dnmt3b-/- mice.
Project description:Pancreatic adenocarcinoma (PDAC) is one of the most lethal human malignancies and a major health problem. Patient-derived xenografts (PDX) are appearing as a prime approach for preclinical studies despite being insufficiently characterized as a model of the human disease and its diversity. We generated subcutaneous PDX from PDAC samples obtained either surgically or using diagnostic biopsies (endoscopic ultrasound guided fine needle aspirate). The extensive multiomics characterization of the xenografts demonstrated that PDX is a suitable model for preclinical studies, representing the diversity of the primary cancers. the variable MultiOmicsClassification indicates the resulting sample's group. Whole-genome DNA methylation was analyzed using the Illumina Infinium HumanMethylation450 Beadchips. Integragen SA (Evry, France) carried out microarray experiments and hybridized to the BeadChip arrays following the manufacturer’s instructions. Illumina GenomeStudio software was used to extract the beta value DNA methylation score for each locus. We removed data from probes that contained SNPs or overlapped with a repetitive element that was not uniquely aligned to the human genome or regions of insertions and deletions in the human genome. The CpG Island Methylator Phenotype (CIMP) index was determined using methylation Illumina Infinium HumanMethylation450 BeadChips based on previous low throughput work (Toyota, 1999). In brief, all island CpG found to be unmethylated (<20% Beta-value) in all 25 normal pancreatic samples from the ICGC consortium (Nones, 2014) were selected. The CIMP index was calculated independently for each sample as the proportion of methylated (>30% Beta-value) CpGs among the selected normally unmethylated island CpG.
Project description:Serrated adenocarcinoma (SAC) is a recently recognized colorectal cancer (CRC) subtype accounting for 7.5 - 8.7% of CRCs. It has been shown that SAC has a worse prognosis and has different molecular and immunohistochemical features compared to conventional carcinoma (CC) but, to date, there is no study analysing its methylome profile. We have investigated the methylation status of 450,000 CpG sites using the Infinium Human Methylation 450 BeadChip array in 103 colorectal specimens from Spanish and Finnish patients. The comparison between the epigenetic signature of 36 SACs and 34 matched CCs was established with the aim of identifying the functions which characterize SAC biology and also the most differentially methylated genes for subsequent validatation by pyrosequencing, methylation-specific PCR, qPCR and immunohistochemistry, including additional cases. Microarray data showed a higher representation of morphogenesis-, neurogenesis-, cytoskeleton- and vesicle-transport-related functions and also significant differential methylation of 15 genes, including the iodothyronine deiodinase DIO3 and the forkhead family transcription factor FOXD2 genes which were validated at the CpG, mRNA and protein level. A quantification study of the methylation status of CpG sequences in FOXD2 demonstrated a novel region controlling gene expression. Moreover, differences in these markers were also evident when comparing SAC with CRC showing molecular and histological features of high level microsatellite instability. This methylome study demonstrates that SAC has a distinct epigenetic regulation pattern resulting in different biological functions and that DIO3 and FOXD2 might be molecular targets for a specific histology-oriented treatment of CRC. HumanMethylation450K BeadChip (Illumina, Inc, San Diego, CA), using Infinium HD Methylation assay for genome-wide DNA methylation screening, was employed. In brief, genomic DNA (1000 ng) from each sample was bisulfite converted with the EZ DNA Methylation Kit (Zymo Research, Orange, CA) according to the manufacturer´s recommendations. Bisulfite-treated DNA was isothermally amplified at 37°C (20-24h) and the DNA product was fragmented by an endpoint enzymatic process, then precipitated, resuspended, applied to an Infinium Human Methylation450K BeadChip (Illumina, San Diego, CA, USA) and hybridized at 48°C (16-24h). The fluorescently-stained chip was imaged by the Illumina i-SCAN and Illumina's Genome Studio program (Methylation Module) was used to analyze BeadArray data to assign site-specific DNA methylation β-values to each CpG site.
Project description:Epigenetic methyl-CpG silencing of the ribosomal RNA (rRNA) genes is thought to down-regulate rRNA synthesis in mammals. In contrast, we now show that CpG methylation in fact positively influences rRNA synthesis and processing. Human HCT116 cells, inactivated for DNMT1 and DNMT3b or treated with aza-dC, lack CpG methylation and reactivate a large fraction of normally silent rRNA genes. Unexpectedly, these cells display reduced rRNA synthesis and processing, and accumulate unprocessed 45S rRNA. Reactivation of the rRNA genes is associated with their cryptic transcription by RNA polymerase II. Ectopic expression of cryptic rRNA gene transcripts recapitulates the defects associated with loss of CpG methylation. The data demonstrate that rRNA gene silencing prevents cryptic RNA polymerase II transcription of these genes. Lack of silencing leads to the partial disruption of rRNA synthesis and rRNA processing, providing an unexpected explanation for the cytotoxic effects of loss of CpG methylation. Agilent custom microarray analyses of transcripts from sense and antisense strands of the human rRNA genes present in total nuclear RNA from HCT116-DNMT1-/-;DNMT3b-/- (DKO) and HCT116 (PS) cells. The DKO/PS RNA ratio was normalized within the 5’ region of the 45S ribosomal RNA, since this sense coding region was found by quantitative Northern and S1-mapping analyses to equally present in the RNA pools from both cells (as compared to total RNA levels and 18S and 28S levels). The distribution for sense RNAs from the coding region is strongly influenced by the predominant RPI 45S rRNA transcript and hence peaks at 0, the DKO and PS 45S rRNA signals having been normalized. 60-mer probes were designed to tile Human rDNA (GenBank accession U13369) on both strands using ArrayOligoSelector (Wardle et al., 2006). A total of 1,146 different non-overlapping probes (573 for each DNA strand) were designed to cover the 43 kb of human rDNA and each printed in triplicate on the array. The experiment was performed using a dye-swap duplicate analysis. The microarrays were scanned on a G2565CA DNA microarray scanner (Agilent Technologies) and the quantification performed using the Feature Extraction software (Agilent technologies). The data were analyzed using the LIMMA software package in R (Smyth and Speed, 2003).