Mirror bisulfite sequencing – a method for single-base resolution of hydroxymethylcytosine
ABSTRACT: While the role of 5-methylcytosine has been well studied, the biological role of 5-hydroxymethylcytosine still remains unclear due to the limited methods available for single-base detection of 5-hydroxymethylcytosine (5hmC). Here we present Mirror bisulfite sequencing for the detection of 5hmC at a single CpG site by synthesizing a DNA strand to mirror the parental strand. This semi-conservative duplex is sequentially treated with β-glucosyltransferase and M.SssI methylase. A glucosyl-5hmCpG in the parental strand inhibits methylation of the mirroring CpG site, and after bisulfite conversion, a thymine in the mirroring strand indicates a 5hmCpG site in the parental strand whereas a cytosine indicates a non-5hmC site. Using this method, the 5hmC levels of various human tissues and paired tumor liver tissues were mapped genome-wide. Overall design: developing a new assay for genomic profiling of 5hmC
Project description:Mapping genome-wide 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC) at single-base resolution is important to understand their biological functions. We present a cost-efficient mapping method that combines 5hmC-specific restriction enzyme PvuRts1I with a 5hmC enrichment method. The sensitive method enables detection of low abundant 5hmC sites, providing a more complete 5hmC landscape than available bisulfite-based methods. This method generated the first genome-wide 5fC map at single-base resolution. Parallel analyses revealed that 5hmC and 5fC existed with lower abundance and more dynamically in non-CpG context than in CpG context. In the genic region, distribution of 5hmCpG and 5fCpG differed from 5hmCH and 5fCH (H=A, T, C). 5hmC and 5fC were distributed distinctly at regulatory protein-DNA binding sites, depleted in permissive transcription factor binding sites, and enriched at active and poised enhancers. This sensitive bisulfite-conversion free method can be applied to biological samples with limited starting material or low abundance of cytosine modifications. Sensitive mapping of genome-wide 5-hydroxymethylcytosine and 5-formylcytosine in mouse embryonic stem cell at single-base resolution by combining 5-hydroxymethylcytosine specific restriction enzyme PvuRts1I and 5-hydroxymethylcytosine enrichment method (selective chemical labeling or SEAL)
Project description:The epigenetic DNA modification 5-hydroxymethylcytosine (5hmC) has crucial roles in development and gene regulation. Quantifying the abundance of this epigenetic mark at the single-cell level could enable us to understand its roles. We present a single-cell, genome-wide and strand-specific 5hmC sequencing technology based on 5hmC glucosylation and glucosylation-dependent digestion of DNA, that reveals pronounced cell-to-cell variability in the abundance of 5hmC on the two DNA strands of a given chromosome. We develop a mathematical model that reproduces the strand bias and use this model to make two main predictions. First, the variation in strand bias should decrease when 5hmC turnover increases. Second, the strand bias of two sister cells should be strongly anti-correlated. We validate these predictions experimentally, and use our model to reconstruct lineages of 2- and 4-cell mouse embryos, showing that single-cell 5hmC sequencing can be used as a lineage reconstruction tool. Overall design: In this study, 5-hydroxymethylcytosine (5hmC) was detected on a genome-wide level in single cells from E14tg2a (E14) mouse embryonic stem cells, Vitamin C treated E14 cells, B6/CBA mouse oocytes, 2-cell mouse embryos and 4-cell mouse embryos using a new method called as scAba-seq.
Project description:In human and mouse stem cells and brain, 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) can occur outside of CG dinucleotides. Using protein binding microarrays (PBMs) containing 60-mer DNA probes, we evaluated the effect of 5mC and 5hmC on one DNA strand on the double-stranded DNA binding of the mouse B-ZIP transcription factors (TFs) CREB1, ATF1, and JUND. 5mC inhibited CREB1 binding to the canonical CRE half-site |GTCA, but increased binding to the C/EBP half-site |GCAA. 5hmC inhibited CREB1 binding to all 8-mers except TGAT|GCAA, where binding is enhanced. We observed similar DNA binding patterns with the closely related TF: ATF1. In contrast, both 5mC and 5hmC inhibited binding of JUND. These results identify new DNA sequences that are well-bound by CREB1 and ATF1 only when they contain 5mC or 5hmC. Analysis of two x-ray structures examines the consequences of 5mC and 5hmC on DNA binding by CREB and FOS|JUN. Overall design: Protein binding microarray (PBM) experiments were performed for a set of 3 mouse B-ZIP transcription factors, CREB1, ATF1, and JUND. Briefly, the PBMs involved binding GST-tagged DNA-binding proteins to double-stranded 44K Agilent microarrays (Berger et al., Nature Biotechnology 2006) in order to determine their binding preferences to sequences containing modified cytosines. We modified the double stranding step of the PBM protocol in which the nucleotide mixture contained 5-methylcytosine or 5-hydroxymethylcytosine. Details of the modified cytosine PBM protocol are described in Khund-Sayeed S et al., Integrative Biology, 2016.
Project description:Active DNA demethylation in mammals involves TET-mediated iterative oxidation of 5-methylcytosine (5mC)/5-hydroxymethylcytosine (5hmC) and subsequent excision repair of highly oxidized cytosine bases 5-formylcytosine (5fC)/5-carboxylcytosine (5caC) by Thymine DNA glycosylase (TDG). However, quantitative and high-resolution analysis of active DNA demethylation activity remains challenging. Here we describe M.SssI methylase-assisted bisulfite sequencing (MAB-seq), a method that directly maps 5fC/5caC at single-base resolution. Genome-wide MAB-seq allows systematic identification of 5fC/5caC in Tdg-depleted embryonic stem cells, thereby generating a base-resolution map of active DNA demethylome. A comparison of 5fC/5caC and 5hmC distribution maps indicates that catalytic processivity of TET enzymes correlates with local chromatin accessibility. MAB-seq also reveals strong strand asymmetry of active demethylation within palindromic CpGs. Integrating MAB-seq with other base-resolution mapping methods enables quantitative measurement of cytosine modification states at key transitioning steps of active demethylation pathway, and reveals a regulatory role of 5fC/5caC excision repair in active DNA demethylation cascade. Analysis of 5fC/5caC excision repair-dependent active DNA demethylome by MAB-seq in mouse embryonic stem cells.
Project description:We present here a novel approach called Reduced Representation 5-Hydroxymethylcytosine Profiling (RRHP), which exploits β-glucosyltransferase (β-GT) to inhibit restriction digestion at adapters ligated to a genomic library, such that only fragments presenting glucosylated 5hmC residues at adapter junctions will be amplified and sequenced. This assay profiles 5hmC sites with single-base resolution in a strand-specific manner. The absence of harsh chemical conversion steps allows for sequencing of native DNA with less inputs, enhancing both sequencing quality and mapping efficiency. Most importantly, the method proves highly reproducible and is a positive display method, sensitive enough to interrogate 5hmC sites with low abundance. When combined with existing RRBS data, it allows simultaneous comparison of 5mC and 5hmC at specific site. developing a new assay for genomic profiling of 5hmC
Project description:The study of 5-hydroxylmethylcytosines (5hmC), the sixth base of the mammalian genome, as an epigenetic mark has been hampered by a lack of method to map it at single-base resolution. Previous affinity purification-based methods could not precisely locate 5hmC nor accurately determine its relative abundance at each modified site. We here present a genome-wide approach for mapping 5hmC at base resolution. Application of this new method to the embryonic stem cells not only confirms widespread distribution of 5hmC in mammalian genome, but also reveals a strong sequence bias and strand asymmetry at sites of 5hmC. Additionally, the relative abundance of 5hmC varies significantly depending on the types of functional sequences, suggesting different mechanisms for 5hmC deposition and maintenance. Furthermore, we observe high levels of 5hmC and reciprocally low levels of 5mC at transcription factor binding sites, revealing a dynamic DNA methylation process at cis-regulatory elements. Base resolution sequencing of 5 hydroxymethylcytosine in human and mouse embryonic stem cells
Project description:We performed a meta analysis of publicly available TET1, 5mC, 5hmC and genome wide bisulfite profiling data mostly from mouse embryonic stem cells (ESC). Genome wide chromatin immunoprecipitation combined with deep sequencing (ChIP-seq) has revealed binding of the TET1 protein at CpG-island (CGI) promoters and at bivalent promoters. We show that TET1 also coincides with DNAseI hypersensitive sites (HS). Presence of TET1 at these THREE locations suggests that it may play a dual role: an active role at CpG-islands and DNAseI hypersensitive sites and a repressive role at bivalent loci. In line with the presence of TET1, significant enrichment of 5hmC but not 5mC is detected at bivalent promoters and DNaseI HS. Surprisingly, 5hmC is not detected or present at very low levels at CGI promoters notwithstanding the presence of TET1 at these loci. Our meta analysis suggest that asymmetric methylation is present at CA- and CT-repeats in the genome of some human ESC. Examination of the distribution of 5-methylcytosine and 5-hydroxymethylcytosine in the genome of mouse embryonic stem cells.
Project description:Cytosine base modifications 5-methylcytosine (5mC), 5-hydroxymethylcytosine (5hmC) and 5-formylcytosine (5fC) are present in mammalian DNA. Here, reduced bisulfite sequencing is developed for quantitatively sequencing 5fC at single-base resolution. This method is then applied with oxidative bisulfite sequencing to gain a map of 5mC, 5hmC and 5fC in mouse embryonic stem cells. 12 samples, reduced representation bisulphite treatment: 4 replicates each for bisulphite (BS), oxidative BS (oxBS) and reduced BS (redBS) for the detection of 5mC, 5hmC and 5fC. Mouse (strain B6C) embryonic stem cells.
Project description:DNA methylation of C5-cytosine (5mC) in the mammalian genome is a key epigenetic event that is critical for various cellular processes. However, how the genome-wide 5mC pattern is dynamically regulated remains a fundamental question in epigenetic biology. The TET family of 5mC hydroxylases, which convert 5mC to 5-hydroxymethylcytosine (5hmC), have provided a new potential mechanism for the dynamic regulation of DNA methylation. The extent to which individual Tet family members contribute to the genome-wide 5mC and 5hmC patterns and associated gene network remains largely unknown. Here we report genome-wide mapping of Tet1 and 5hmC in mESCs and reveal a mechanism of action by which Tet1 controls 5hmC and 5mC levels in mESCs. In combination with microarray and mRNA-seq expression profiling, we identify a comprehensive yet intricate gene network influenced by Tet1. We propose a model whereby Tet1 controls DNA methylation both by binding to CpG-rich regions to prevent unwanted DNA methyltransferase activity, and by converting the existing 5mC to 5hmC through its enzymatic activity. This Tet1-mediated antagonism of CpG methylation imparts differential maintenance of DNA methylation status at Tet1 target loci, thereby providing a new regulatory mechanism for establishing the epigenetic landscape of mESCs, which ultimately contributes to mESC differentiation and the onset of embryonic development. To determine the genome-wide DNA methylation changes caused by Tet1 depletion in mouse ES cells. Tet1 protein was depleted by specific siRNA treatment. The DNA methylation levels in control and Tet1 siRNA-transfected ES cells were determined by targeted bisulfite sequencing.
Project description:Hydroxymethylcytosine (5hmC) was recently found to be abundantly present in certain cell types including embryonic stem cells. The function of 5hmC is poorly understood. Here we have generated a genome-wide map of 5hmC in human embryonic stem cells (hESCs) by hydroxymethyl-DNA immunoprecipitation followed by massively parallel sequencing (hmeDIP-seq). We found that 5hmC is enriched over enhancers as well as gene bodies, suggesting a potential role of 5hmC in gene regulation. Consistent with localization of 5hmC at enhancers, 5hmC was significantly enriched in histone modifications associated with enhancers such as H3K4me1 and H3K27ac. 5hmC was enriched in other protein-DNA interaction sites such as OCT4 and NANOG binding sites. Furthermore we found that 5hmC regions tend to be GC-skewed (excess G over C on one strand of DNA). These findings suggest that 5hmC may be targeted to certain genomic regions based both on gene expression and sequence composition. Overall design: 2 experiments, 2 controls