Project description:Enzymatic erasure of DNA methylation in mammals involves iterative 5-methylcytosine (5mC) oxidation by the ten-eleven translocation (TET) family of DNA dioxygenase proteins. As the most abundant form of oxidized 5mC, the prevailing model considers 5-hydroxymethylcytosine (5hmC) as a key nexus in active DNA demethylation that can either indirectly facilitate replication-dependent depletion of 5mC by inhibiting maintenance DNA methylation machinery (UHRF1/DNMT1), or directly be iteratively oxidized to 5-formylcytosine (5fC) and 5-carboxycytosine (5caC) and restored to cytosine (C) through thymine DNA glycosylase (TDG)-mediated 5fC/5caC excision repair. In proliferative somatic cells, to what extent TET-dependent removal of 5mC entails indirect DNA demethylation via 5hmC-induced replication-dependent dilution or direct iterative conversion of 5hmC to 5fC/5caC is unclear. Here we leverage a catalytic processivity stalling variant of human TET1 (TET1.var: T1662E) to decouple the stepwise generation of 5hmC from subsequent 5fC/5caC generation, excision and repair. By using a CRISPR/dCas9-based epigenome-editing platform, we demonstrate that 5fC/5caC excision repair (by wild-type TET1, TET1.wt), but not 5hmC generation alone (by TET1.var), is requisite for robust restoration of unmodified cytosines and reversal of somatic silencing of the methylation-sensitive, germline-specific RHOXF2B gene promoter. Furthermore, integrated whole-genome multi-modal epigenetic sequencing reveals that hemi-hydroxymethylated CpG dyads predominantly resist replication-dependent depletion of 5mC on the opposing strand in TET1.var-expressing cells. Notably, TET1.var-mediated 5hmC generation is sufficient to induce similar levels of differential gene expression (compared to TET1.wt) without inducing major changes in unmodified cytosine profiles across the genome. Our study suggests 5hmC alone plays a limited role in driving replication-dependent DNA demethylation in the presence of functional DNMT1/UHRF1 mechanisms, but can regulate gene expression as a bona fide epigenetic mark in proliferative somatic cells.

Project description:Differentiation of CD4+T-cells into effector subsets is a critical component of the adaptive immune system and an incorrect response can lead to autoimmunity or immune deficiency. Cellular differentiation including T-cell differentiation is accompanied by large-scale epigenetic remodeling, including changes in DNA methylation at key regulators of T-cell differentiation. The TET family of enzymes were recently shown to be able to catalyse methylated cytosine (5mC) into 5-hydroxymethylcytosine (5hmC) enabling a pathway of active removal of DNA methylation. Here, we characterize 5hmC, 5mC and transcriptional dynamics during human CD4+T-cell polarisation in a time series approach and relate these changes to profiles in ex-vivo CD4+memory subsets. We observed large-scale remodelling during early CD4+T-cell differentiation which was predictive of subsequent changes during late time points, these changes were also related to disease associated regions which we show can act as functional regulatory elements. This dataset was designed to assess how TET1 affects gene expression during human CD4+T-cell differentiation. We observed that TET1 was highly expressed in primary lymphocytes compared to other human tissues and loss of TET1 gene expression was seen within 6 hours of naÃ¯ve CD4+T-cell activation. Primary human naÃ¯ve T-cells were transfected with different TET1 containing plasmids and polarized towards Th1 for 24h. When comparing cells transfected with full length TET1 to catalytically inactive TET1, we observed mis-expression of several cytokine/chemokine genes related to T-cell differentiation. This was not observed for cells expressing the catalytic domain of TET1. Note that the expression array only targets the DNA binding domain of the TET1 gene, therefore we validated ectopic expression of TET1 by qPCR targeting the catalytic domain. This submission contains data from Transcription profiling by array of primary human CD4+T-cells overexpressing TET1 polarized towards Th1. See related experiments: E-MTAB-4686, E-MTAB-4687, E-MTAB-4688, E-MTAB-4689.

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TET1 catalytic activity is required for reprogrammign of imprinting control regions and the patterning of sperm-specific hypomethylated regions [RNA-Seq]

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