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Reduced representation bisulphite sequencing of ten bovine somatic tissues reveals DNA methylation patterns and their impacts on gene expression [RRBS-Seq]

ABSTRACT: As a key epigenetic modification, DNA methylation is essential for normal development by regulating processes like gene expression, genomic imprinting, and suppression of repetitive elements. However, DNA methylation in the cattle genome is not well understood. Here we presented the first single-base-resolution maps of DNA methylation in 10 diversely somatic tissues harvested from the sequenced Hereford cow L1 Dominette 01449 and her relatives using reduced representation bisulphite sequencing (RRBS). In total, we observed 1,868,049 high accuracy cytosines that located in the CG enriched regions. Similar to the methylation patterning in other species, the CG context was predominant methylated. Widespread differences were identified between the methylation patterns of CG and non-CG contexts. They were distributed differentially among the genomic features, including the genic regions, CpG islands, and repetitive sequences. Autocorrelation analysis among adjacent residues illustrated that methylation level of CGs were highly correlated in a region. In contrast, weak or no correlation was found among non-CGs or between CGs and non-CGs. The distinct distribution and low correlation of CG and non-CG methylation suggested that non-CG methylation may be independent from CG methylation and may be mediated by different mechanisms. We also detected 798 tissue-specific differentially methylated cytosines (tDMC) and 131 tissue-specific differentially methylated CpG islands. Combined analysis with the RNA-seq data, we discovered several non-CGs in tDMCs also highly correlated with gene expression, which implied the potential function of non-CG methylation in somatic cells in addition to pluripotent cells. In summary, we showed that non-CGs exist in bovine tissues and some of them were correlated with tissue-specific functions. This study provided essential information for the cytosine methylation patterning in bovine somatic tissues.

ORGANISM(S): Bos taurus

PROVIDER: GSE76346 | GEO | 2017/02/14

SECONDARY ACCESSION(S): PRJNA306952

REPOSITORIES: GEO

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Project description:Methylation is a repressive modification of DNA prevalent throughout mammalian genomes yet mostly absent at CG rich stretches referred to as CGI. Here we identify their building principles by parallel genomic targeting of sequence libraries. Iterative insertions generated over 3,000 variants of genome-derived and artificial sequences at the same genomic site. Single molecule profiling of the methylation status of this collection allowed modeling the contribution of CG content and DNA binding factors towards the unmethylated state. It made the surprising prediction that the majority of CGs within endogenous islands are susceptible to methylation changes modulated by the presence of transcription factors, which is indeed confirmed by genome-wide methylation dynamics during multiple cellular differentiations. Our model further predicts blocks of constitutively unmethylated CGs independent from TF binding, which have a median size of ~300bp but are only present in half of all islands. Their constitutively unmethylated state is a hallmark of untransformed cells but their increased methylation is a specific and predictive feature of cancer. This study quantifies the two principal mechanisms governing methylation patterns in mammalian genomes. It provides a framework to interpret methylation data across normal and cancer samples and refines the concept of CpG islands. Methylation is a repressive modification of DNA prevalent throughout mammalian genomes yet mostly absent at CG rich stretches referred to as CGI. Here we identify their building principles by parallel genomic targeting of sequence libraries. Iterative insertions generated over 3,000 variants of genome-derived and artificial sequences at the same genomic site. Single molecule profiling of the methylation status of this collection allowed modeling the contribution of CG content and DNA binding factors towards the unmethylated state. It made the surprising prediction that the majority of CGs within endogenous islands are susceptible to methylation changes modulated by the presence of transcription factors, which is indeed confirmed by genome-wide methylation dynamics during multiple cellular differentiations. Our model further predicts blocks of constitutively unmethylated CGs independent from TF binding, which have a median size of ~300bp but are only present in half of all islands. Their constitutively unmethylated state is a hallmark of untransformed cells but their increased methylation is a specific and predictive feature of cancer. This study quantifies the two principal mechanisms governing methylation patterns in mammalian genomes. It provides a framework to interpret methylation data across normal and cancer samples and refines the concept of CpG islands. Libraries of DNA sequences were constructed either by mouse genome (129S6) or E.coli genome (NC_010473.1) subrepresentation or custom synthesis. DNA fragments were inserted into the genome of mouse embryonic stem cells by recombination mediated casette exchange (RMCE) at the B-globin locus. Methylation status of the inserted DNA sequences was profiled by bisulfite sequencing using a pair of universal primers flanking the fragments.

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Reduced representation bisulphite sequencing of ten bovine somatic tissues reveals DNA methylation patterns and their impacts on gene expression [RRBS-Seq]

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