Project description:Enzymes catalysing the methylation of the 5-position of cytosine (mC) have essential roles in regulating gene expression and maintaining cellular identity. Recently, TET1 was found to hydroxylate the methyl group of mC, converting it to 5-hydroxymethyl cytosine (hmC). Here we show that TET1 binds throughout the genome of embryonic stem cells, with the majority of binding sites located at transcription start sites (TSSs) of CpG-rich promoters and within genes. The hmC modification is found in gene bodies and in contrast to mC is also enriched at CpG-rich TSSs. We provide evidence further that TET1 has a role in transcriptional repression. TET1 binds a significant proportion of Polycomb group target genes. Furthermore, TET1 associates and colocalizes with the SIN3A co-repressor complex. We propose that TET1 fine-tunes transcription, opposes aberrant DNA methylation at CpG-rich sequences and thereby contributes to the regulation of DNA methylation fidelity.
Project description:We analyzed the genome-wide binding of Tet1 in control (shScr) and Tet1 knockdown (shTet1) mouse ES cells using two different Tet1 antibodies (Tet1-C and Tet1-N). Furthermore, we generated genome-wide mapping of hydroxymethyl cytosine (hmC) and methyl cytosine (mC). We find that hmC, in contrast to mC, is also found at transcription start sites (TSSs), and that there is a significant overlap between Tet1 binding and hmC positive regions. Surprisingly, our results also suggest, that Tet1 has a role in transcriptional repression. We showed that Tet1 associates with Sin3A co-repressor complex, and by performing ChIP-sequencing of Sin3A, we find co-localisation of Tet1 and Sin3a throughout the genome
Project description:Enzymes catalyzing the methylation of the 5-position of cytosine (mC) have essential roles in regulating gene expression, genome stability, and maintaining cellular identity. Recently Tet1, which is highly expressed in embryonic stem (ES) cells, was found to oxidize the methyl group of mC converting it to 5-hydroxymethyl cytosine (hmC)3. Here, we present the genome-wide mapping of Tet1 and hmC in mouse ES cells. We show that Tet1 binds throughout the genome with the majority of binding sites located at transcription start sites (TSSs) and within genes. Similar to Tet1 and mC, also hmC is found throughout the genome and in particular in gene bodies. However, in contrast to mC, hmC is enriched at TSSs. Tet1 and hmC are associated with genes critical for the control of development and differentiation, which become methylated during differentiation. Surprisingly our results also suggest that Tet1 has a role in transcriptional repression. We show that Tet1 binds to a significant proportion of target genes that are positive for the Polycomb repressive histone mark H3K27me3, and that downregulation of Tet1 also leads to increased expression of a group of Tet1 target genes. In agreement with a potential repressive function, we show that Tet1 associates with the Sin3A co-repressor complex, which also co-localises with Tet1 throughout the genome. We propose that Tet1 fulfils dual functions in transcriptional regulation, where it fine-tunes DNA methylation and associates with the Sin3A co-repressor complex to prevent transcriptional activation.