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Robust bisulfite free SMRT Sequencing of mdC based on a novel hpTet3-enzyme

ABSTRACT: Genomic DNA contains next to the four canonical nucleosides dA, dC, dG and T the additional base 5-methyldeoxycytidine (mdC). The presence of this methylated cytidine nucleoside in promoter regions or gene bodies has an instrumental effect on the transcriptional activity of the corresponding gene. The methylation patterns of genes are therefore responsible for either silencing or activation of genes. Sequencing of mdC positions in the genome is consequently of paramount importance for early cancer diagnostics in order to determine incorrect expression of genes. Today, the bisulfite method is the gold standard for mdC-sequencing, which has however the caveat that the majority of the input DNA is degraded during the bisulfite treatment. In addition, bisulfite sequencing is rather error prone. Here we report a benign, bisulfite free mdC sequencing method based on 3rd generation single molecule SMRT sequencing. The fundament of the technology is a new Tet3 enzyme that oxidizes mdCs with high efficiency to 5-carboxycytidine (cadC). caC in turn provides and excellent read out by SMRT sequencing using specially trained AI-based algorithms.

ORGANISM(S): Escherichia phage Lambda

PROVIDER: GSE256446 | GEO | 2024/11/20

REPOSITORIES: GEO

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Project description:It has widely accepted that 5-methylcytosine is the only form of DNA methylation in mammalian genomes, whereas the other forms, such as N6-methyladenine, primarily exist in prokaryotes and only a few eukaryotes. Herein, we demonstrated the surprising presence of N6-methyladenine in mammalian genomes, especially, mouse embryonic stem cells. This modification is enriched at histone variant H2A.X-deposited genomic regions in wild type embryonic stem cells. Our work also showed that a previously unknown DNA demethylase, Alkbh1, is the major demethylase for N6-methyladenine in embryonic stem cells. Increase of N6-methyladenine levels in Alkbh1 deficient cells leads to silencing of genes that regulate embryonic development. Surprisingly, genes located on the X-chromosome, but not the Y-chromosome or autosomes are preferentially silenced by N6-methyladenine. Strikingly, N6-methyladenine in Alkbh1 deficient cells are specifically deposition at young, full-length subfamilies of LINE1 transposons that are strongly enriched on the X chromosome. Furthermore, N6-methyladenine deposition on LINE1s pattern is inversely correlated with their evolutionary age. The deposition of N6-methyladenine results in epigenetic silencing of such L1s, which are otherwise actively transcribed in wild type embryonic stem cells, and the neighboring enhancers and genes. Furthermore, N6-methyladenine induced-silencing resists gene activation signals during embryonic stem cell differentiation. Thus, N6-methyladenine adopts a new function in epigenetic silencing in evolution, distinct from its role in gene activation in other organisms. In summary, our results demonstrate that N6-methyladenine unexpectedly constitutes a crucial component of the epigenetic regulation repertoire in mammalian genomes. First, we used a native-ChIP approach to enrich for DNA molecules residing in H2A.X-deposition regions in mouse ESCs as previously described. Then, co-purified DNA molecules from WT or KO ESCs were subject to SMRT sequencing and data analysis for DNA modifications (Pacific Biosciences). H2A.X Native ChIP coupling with SMRT sequencing (separate the short "S" and long "L" part to sequencing)

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Robust bisulfite free SMRT Sequencing of mdC based on a novel hpTet3-enzyme

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