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Base-resolution analyses of sequence and parent-of-origin dependent DNA methylation in the mouse genome.

ABSTRACT: Differential methylation of the two parental genomes in placental mammals is essential for genomic imprinting and embryogenesis. To systematically study this epigenetic process, we have generated a base-resolution, allele-specific DNA methylation (ASM) map in the mouse genome. We find parent-of-origin dependent (imprinted) ASM at 1,952 CG dinucleotides. These imprinted CGs form 55 discrete clusters including virtually all known germline differentially methylated regions (DMRs) and 23 previously unknown DMRs, with some occurring at microRNA genes. We also identify sequence-dependent ASM at 131,765 CGs. Interestingly, methylation at these sites exhibits a strong dependence on the immediate adjacent bases, allowing us to define a conserved sequence preference for the mammalian DNA methylation machinery. Finally, we report a surprising presence of non-CG methylation in the adult mouse brain, with some showing evidence of imprinting. Our results provide a resource for understanding the mechanisms of imprinting and allele-specific gene expression in mammalian cells.

SUBMITTER: Xie W

PROVIDER: S-EPMC3343639 | biostudies-literature | 2012 Feb

REPOSITORIES: biostudies-literature

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Base-resolution analyses of sequence and parent-of-origin dependent DNA methylation in the mouse genome.

Xie Wei W Barr Cathy L CL Kim Audrey A Yue Feng F Lee Ah Young AY Eubanks James J Dempster Emma L EL Ren Bing B

Cell 20120201 4

Differential methylation of the two parental genomes in placental mammals is essential for genomic imprinting and embryogenesis. To systematically study this epigenetic process, we have generated a base-resolution, allele-specific DNA methylation (ASM) map in the mouse genome. We find parent-of-origin dependent (imprinted) ASM at 1,952 CG dinucleotides. These imprinted CGs form 55 discrete clusters including virtually all known germline differentially methylated regions (DMRs) and 23 previously ...[more]

PMID: 22341451

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Project description:Allele specific DNA methylation (ASM) is crucial for genomic imprinting and mammalian development. Here we present a base-resolution, genome-wide allelic DNA methylation map for both CG and non-CG sites in the mouse brain. We found parent-of-origin dependent (imprinted) ASM at 1,952 CGs which form 55 discrete clusters. This uncovers 31 reported differentially methylated regions (DMRs), including virtually all known germline DMRs, and 24 novel candidate DMRs with some occurring at microRNA genes. In the same adult tissue we also report a surprising presence of non-CG methylation with some showing evidence of imprinting. Finally, we identified sequence dependent ASM at 131,765 CGs. Interestingly, methylation at these sites exhibits a strong dependence on the immediate adjacent bases, allowing us to define a conserved sequence preference for the mammalian DNA methylation machinery. Our genome-wide ASM map should help with understanding the epigenetic differences between two parental genomes in mammals. The crosses of the two mouse strains 129x1/SvJ (129) and Cast/EiJ (Cast) were performed at Jackson Laboratories (http://jaxmice.jax.org/) and the male mice F1 offspring and males of each of the two parental strains were shipped to investigator laboratories at 8 to 9 weeks of age. The frontal cortex from the F1 crosses of the two mouse lines was dissected and the RNA was isolated followed by two DNAseI treatments to remove DNA contaminant. The presence of DNA in the RNA was tested using quantitative PCR and probes designed to span exons. The quality of the RNA was determined by the Agilent 2100 Bioanalyzer prior to the construction of the libraries. RNA was treated with RiboMinus (Invitrogen, Carlsbad CA) to remove the ribosomal RNA. The methods for the preparation of the libraries are outlined in the Whole Transcriptome library preparation for SOLiD sequencing protocol (https://www3.appliedbiosystems.com/cms/groups/mcb_support/documents/generaldocuments/cms_065852.pdf). Briefly, RNA depleted of ribosomal RNA was fragmented using RNAseIII. Purified RNA was hybridized and ligated to primers then converted to cDNA using reverse transcriptase. The cDNA was size selected to contain 50 to 150 bp inserts then purified and amplified prior to sequencing. Libraries were constructed with RNA from three independent mice (3 biological replicates) for each of the experimental crosses. Sequencing was performed at EdgeBio (http://www.edgebio.com/) and the data from the 3 mice for each experimental cross line were combined given the high correlation between each of the libraries (R >0.98).

Project description:The supernumerary chromosome 21 in Down syndrome differentially affects the methylation statuses at CpG dinucleotide sites and creates genome-wide transcriptional dysregulation of parental alleles, ultimately causing diverse pathologies. At present, it is unknown whether those effects are dependent or independent of the parental origin of the nondisjoined chromosome 21. Linkage analysis is a standard method for the determination of the parental origin of this aneuploidy, although it is inadequate in cases with deficiency of samples from the progenitors. Here, we assessed the reliability of the epigenetic 5mCpG imprints resulting in the maternally (oocyte)-derived allele methylation at a differentially methylated region (DMR) of the candidate imprinted WRB gene for asserting the parental origin of chromosome 21. We developed a methylation-sensitive restriction enzyme-specific PCR assay, based on the WRB DMR, across single nucleotide polymorphisms (SNPs) to examine the methylation statuses in the parental alleles. In genomic DNA from blood cells of either disomic or trisomic subjects, the maternal alleles were consistently methylated, while the paternal alleles were unmethylated. However, the supernumerary chromosome 21 did alter the methylation patterns at the RUNX1 (chromosome 21) and TMEM131 (chromosome 2) CpG sites in a parent-of-origin-independent manner. To evaluate the 5mCpG imprints, we conducted a computational comparative epigenomic analysis of transcriptome RNA sequencing (RNA-Seq) and histone modification expression patterns. We found allele fractions consistent with the transcriptional biallelic expression of WRB and ten neighboring genes, despite the similarities in the confluence of both a 17-histone modification activation backbone module and a 5-histone modification repressive module between the WRB DMR and the DMRs of six imprinted genes. We concluded that the maternally inherited 5mCpG imprints at the WRB DMR are uncoupled from the parental allele expression of WRB and ten neighboring genes in several tissues and that trisomy 21 alters DNA methylation in parent-of-origin-dependent and -independent manners.

Dataset Information

Base-resolution analyses of sequence and parent-of-origin dependent DNA methylation in the mouse genome.

Publications

Base-resolution analyses of sequence and parent-of-origin dependent DNA methylation in the mouse genome.

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