Project description:To study the role of tet3 and 5-hydroxymethylation in mouse intestine homeostasis our objectives are: To determine the cell types that show a 5hmC reduction level in the absence of Tet3. Identify the role of Tet3 on transcriptional regulation in the small intestinal epithelium. Define the physiological functions impaired in Tet3 -/- small intestine epithelium.
Project description:To define TET3 function in cell differentiation, we profiled the intestinal epithelium at the single-cell level from wild-type and Tet3 knockout mice. Our works shows that, in the absence of TET3, enterocytes exhibit an aberrant differentiation trajectory and do not acquire a physiological cell identity due to an impairment in oxidative phosphorylation, specifically due to the reduced expression of genes encoding for ATP synthase membrane domain subunits. To assess whether the downregulation of ATP synthase subunits upon TET3 loss was due to a TET3 catalytic or non-catalytic activity, we examined global DNA methylation patterns in wild-type and Tet3 knockout intestinal epithelium by whole-genome bisulfite sequencing (WGBS). Our results show that these critical ATP synthase subunits coding-genes did not show any hyperDMR in their regulatory regions, excluding TET3 catalytic activity as the mechanism underlying their decreased gene expression and, pointing thus to TET3 non-catalytic activity.
Project description:Ten-eleven-translocation (TET) proteins catalyze DNA hydroxylation, playing an important role in demethylation of DNA in mammals. Remarkably, although hydroxymethylation levels are high in the mouse brain, the potential role of TET proteins in adult neurogenesis is unknown. We show here that a non-catalytic action of TET3 is essentially required for the maintenance of the neural stem cell (NSC) pool in the adult subventricular zone (SVZ) niche by preventing premature differentiation of NSCs into non-neurogenic astrocytes. This occurs through direct binding of TET3 to the paternal transcribed allele of the imprinted gene Small nuclear ribonucleoprotein-associated polypeptide N (Snrpn), contributing to transcriptional repression of the gene. The study also identifies BMP2 as an effector of the astrocytic terminal differentiation mediated by SNRPN. Our work describes a novel mechanism of control of an imprinted gene in the regulation of adult neurogenesis through an unconventional role of TET3.
Project description:Ten-eleven translocation (Tet) hydroxylases (Tet1-3) oxidize 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC). In neurons increased 5hmC levels within gene bodies correlate positively with gene expression. The mechanisms controlling Tet activity and 5hmC levels are poorly understood. In particular, it is not known how the neuronal Tet3 isoform lacking a DNA binding domain is targeted to the DNA. To identify factors binding to Tet3 we screened for proteins that co-precipitate with Tet3 from mouse retina and identified the transcriptional repressor Rest as a highly enriched Tet3-specific interactor. Rest was able to enhance Tet3 hydroxylase activity after co-expression and overexpression of Tet3 activated transcription of Rest-target genes. Moreover, we found that Tet3 also interacts with Nsd3 and two other H3K36 methyltransferases and is able to induce H3K36 trimethylation. We propose a mechanism for transcriptional activation in neurons that involves Rest-guided targeting of Tet3 to the DNA for directed 5hmC-generation and Nsd3-mediated H3K36 trimethylation.
Project description:Tet3 is an Fe2+-dependent enzyme that oxidizes genomic 5-methylcytosine to 5-hydroxymethylcytosine with the help of alpha-ketoglutarate and oxygen. It is the most abundant Tet enzyme in differentiated tissues including brain. Adult brain contains the highest 5-hydroxymethylcytosine levels. How alpha-ketoglutarate is made available for the oxidation of mC in brain cells and how the Tet activity is linked to neural activity are unsolved questions. Our experiments with full mouse brains show that Tet3 interacts in the nucleus directly with selected enzymes of the mitochondrial citric acid cycle. This leads to the formation of isocitrate. Tet3 also interacts with aspartate aminotransferase, which produces oxaloacetate. Although oxaloacetate and isocitrate are biosynthetic alpha-ketoglutarate precursors, they function as inhibitors of Tet3 and are needed to protect the reactive Fe2+ center from degrading DNA. The supply of Tet3 with alpha-ketoglutarate is established by a direct interaction of Tet3 with glutamate dehydrogenase (Glud1), which converts the neurotransmitter glutamate directly into alpha-ketoglutarate. This links Tet3 function to neural activity.
Project description:To further investigate the gene expression at different courses in MEFs and Tet3 induced neurons, we have employed whole genome microarray expression profiling as a discovery platform to identify the expression level of specific genes, such as neuronal specific genes, fibrobalst specific genes. The gene expression in mouse embryonic fibroblasts and Tet3 induced neurons at 1, 3, 5, 7 dpi.
Project description:TET enzymes oxidize 5-methylcytosine (5mC) into 5-hydroxymethylcytosine (5hmC), a process thought to be intermediary in an active DNA demethylation mechanism. Notably, 5hmC is highly abundant in the brain and in neuronal cells. Here we show that Tet3 is highly upregulated during neuronal differentiation and necessary to maintain silencing of pluripotency-associated genes in neural precursor cells (NPCs). Indeed, Tet3 knockdown (KD) in NPCs led to a significant increase in Oct4 and Nanog gene expression, with OCT4-positive cells appearing as cellular aggregates. Moreover, Tet3 KD led to a genome-scale loss of DNA methylation and hypermethylation of a small number of CpGs that are notably located at neurogenesis-related genes and at imprinting control regions (ICRs) of three imprinted genes (Peg10, Zrsr1 and Mcts2). Our results suggest that TET3 plays a pivotal role in maintaining neural stem cell identity and DNA methylation levels in neural precursor cells, and point to a non-catalytic role for TET3 in neural differentiation.
Project description:Tet3 converts 5-methylcyotsine to 5-hydroxymethylcytosine (5hmC), although it remains unclear how its functions can be regulated. We showed that Tet3 is phosphorylated by cyclin-dependent kinase 5 at a highly conserved serine residue within its catalytic domain, which leads to an increase in its dioxygenase activity in vitro. Interestingly, when stably expressed in Tet triple-knockout mouse embryonic stem cells (mESCs), wild-type Tet3 elicited higher 5hmC enrichment and expression of genes involved in neurogenesis whereas phosphor-mutant Tet3 caused elevated 5hmC and expression of metabolic pathways genes. Expression of wild-type, but not phosphor-mutant Tet3 in Tet3-knockout mESCs, causes optimal expression of BRN2, Hes1 and Hey2 transcription factors which lead to robust terminal differentiation measured by MAP2 expression. Taken together, our results suggest that cdk5-mediated phosphorylation of Tet3 ensures robust activation of neuronal transcriptional programs during differentiation.