TET Enzymes in the Immune System: From DNA Demethylation to Immunotherapy, Inflammation, and Cancer.

Ten-eleven translocation (TET) proteins are iron-dependent and α-ketoglutarate-dependent dioxygenases that sequentially oxidize the methyl group of 5-methylcytosine (5mC) to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC) and 5-carboxylcytosine (5caC). All three epigenetic modifications are intermediates in DNA demethylation. TET proteins are recruited by transcription factors and by RNA polymerase II to modify 5mC at enhancers and gene bodies, thereby regulating gene expression during development, cell lineage specification, and cell activation. It is not yet clear, however, how the established biochemical activities of TET enzymes in oxidizing 5mC and mediating DNA demethylation relate to the known association of TET deficiency with inflammation, clonal hematopoiesis, and cancer. There are hints that the ability of TET deficiency to promote cell proliferation in a signal-dependent manner may be harnessed for cancer immunotherapy. In this review, we draw upon recent findings in cells of the immune system to illustrate established as well as emerging ideas of how TET proteins influence cellular function. Expected final online publication date for the Annual Review of Immunology, Volume 42 is April 2024. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

OGT prevents DNA demethylation and suppresses the expression of transposable elements in heterochromatin by restraining TET activity genome-wide.

The O- GlcNAc transferase OGT interacts robustly with all three mammalian TET methylcytosine dioxygenases. We show here that deletion of the Ogt gene in mouse embryonic stem cells (mESC) results in a widespread increase in the TET product 5-hydroxymethylcytosine (5hmC) in both euchromatic and heterochromatic compartments, with concomitant reduction of the TET substrate 5-methylcytosine (5mC) at the same genomic regions. mESC engineered to abolish the TET1-OGT interaction likewise displayed a genome-wide decrease of 5mC. DNA hypomethylation in OGT-deficient cells was accompanied by de-repression of transposable elements (TEs) predominantly located in heterochromatin, and this increase in TE expression was sometimes accompanied by increased cis -expression of genes and exons located 3' of the expressed TE. Thus, the TET-OGT interaction prevents DNA demethylation and TE expression in heterochromatin by restraining TET activity genome-wide. We suggest that OGT protects the genome against DNA hypomethylation and impaired heterochromatin integrity, preventing the aberrant increase in TE expression observed in cancer, autoimmune-inflammatory diseases, cellular senescence and ageing.

Cellular reprogramming by protein degradation: The next frontier in cancer immunotherapy.

In this issue of Cell Chemical Biology, Lane et al.1 introduce a transgene-based system to express fusion proteins that recruit transcription factors to E3 ligases. This approach expands the target repertoire for engineered cell therapies as exemplified by the targeting of SMAD proteins to overcome a TGFß-mediated suppressive mechanism that weakens anti-tumor responses.

Addressing Perinatal Opioid Use at a Local Health Department in Florida.

PURPOSE: Perinatal substance use disorders (SUDs) remain an urgent public health concern in the United States and are associated with increased maternal and infant morbidity and mortality. Establishing holistic prenatal care among this population allows for engaging or re-engaging the pregnant population in appropriate medical care, including treatment for SUD. DESCRIPTION: The Florida Department of Health in Citrus County (DOH-Citrus) noticed an increase in SUD among their pregnant population and developed a pilot program that incorporates Medication for Opioid Use Disorder (MOUD) and mental health services during routine prenatal care appointments. ASSESSMENT: Since the launch of the pilot program, DOH-Citrus has provided prenatal programs with buprenorphine assistance to 23 members of the community. CONCLUSION: A growing number of local health departments (LHDs) provide harm reduction supplies, overdose prevention education, and local resources for treatment and other life-saving services. In many communities, LHDs are typically the most accessible sources of public health information and health care services. By framing the pilot program as a prenatal care center that incorporates SUD treatment as the prescribed standard of care, DOH-Citrus has implemented a holistic model for treating SUD and reducing barriers while improving continuity of care. LHDs are uniquely positioned to implement harm reduction strategies that address perinatal SUDs, treatment, and recovery within maternal and child health populations. As a health department located in a state without expanded Medicaid and with high rates of uninsured people, this pilot program has the potential to be replicated in other states facing similar challenges.

TET3-mediated DNA oxidation is essential for intestinal epithelial cell response to stressors.

DNA methylation functions as a repressive epigenetic mark that can be reversed by the Ten-eleven translocation (TET) family of DNA dioxygenases that sequentially oxidize 5-methylcytosine into 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). Both 5fC and 5caC can be excised by DNA base-excision repair factors leading to unmodified cytosines. TET enzymes were recently implicated as potential risk factors for inflammatory bowel disease (IBD), but the contribution of TET-mediated DNA oxidation to intestinal homeostasis and response to environmental stressors are unknown. Here, we show prominent roles of TET3 in regulating mouse intestinal epithelial differentiation and response to luminal stressors. Compared with wild-type littermates, mice with intestinal epithelial cell-specific ablation of Tet3 (Tet3ΔIEC) demonstrated a decreased transcriptome involved in innate immune response, Paneth cell differentiation, and epithelial regeneration. Tet3IEC mice exhibited an elevated susceptibility to enteric pathogen infection that is correlated with a decreased epithelial 5hmC abundance. Infection of human enterocytes or mice with the pathogenic bacteria acutely increased 5hmC abundance. Genome-wide 5hmC profiling revealed a shift of genomic enrichment of 5hmC toward genes involved in activating Notch, Wnt, and autophagy pathways. Furthermore, chemical stressor dextran sulfate sodium (DSS) represses epithelial 5hmC abundance in a temporal fashion, and Tet3IEC mice exhibited increased susceptibility to DSS experimental colitis with reduced regenerative capacity. TET3 is a critical regulator of gut epithelial DNA methylome and transcriptome, especially in response to luminal stressors, for the maintenance of tissue homeostasis.

Inducible disruption of Tet genes results in myeloid malignancy, readthrough transcription, and a heterochromatin-to-euchromatin switch.

The three mammalian TET dioxygenases oxidize the methyl group of 5-methylcytosine in DNA, and the oxidized methylcytosines are essential intermediates in all known pathways of DNA demethylation. To define the in vivo consequences of complete TET deficiency, we inducibly deleted all three Tet genes in the mouse genome. Tet1/2/3-inducible TKO (iTKO) mice succumbed to acute myeloid leukemia (AML) by 4 to 5 wk. Single-cell RNA sequencing of Tet iTKO bone marrow cells revealed the appearance of new myeloid cell populations characterized by a striking increase in expression of all members of the stefin/cystatin gene cluster on mouse chromosome 16. In patients with AML, high stefin/cystatin gene expression correlates with poor clinical outcomes. Increased expression of the clustered stefin/cystatin genes was associated with a heterochromatin-to-euchromatin compartment switch with readthrough transcription downstream of the clustered stefin/cystatin genes as well as other highly expressed genes, but only minor changes in DNA methylation. Our data highlight roles for TET enzymes that are distinct from their established function in DNA demethylation and instead involve increased transcriptional readthrough and changes in three-dimensional genome organization.

PSGL-1 attenuates early TCR signaling to suppress CD8+ T cell progenitor differentiation and elicit terminal CD8+ T cell exhaustion.

PSGL-1 (P-selectin glycoprotein-1) is a T cell-intrinsic checkpoint regulator of exhaustion with an unknown mechanism of action. Here, we show that PSGL-1 acts upstream of PD-1 and requires co-ligation with the T cell receptor (TCR) to attenuate activation of mouse and human CD8+ T cells and drive terminal T cell exhaustion. PSGL-1 directly restrains TCR signaling via Zap70 and maintains expression of the Zap70 inhibitor Sts-1. PSGL-1 deficiency empowers CD8+ T cells to respond to low-affinity TCR ligands and inhibit growth of PD-1-blockade-resistant melanoma by enabling tumor-infiltrating T cells to sustain an elevated metabolic gene signature supportive of increased glycolysis and glucose uptake to promote effector function. This outcome is coupled to an increased abundance of CD8+ T cell stem cell-like progenitors that maintain effector functions. Additionally, pharmacologic blockade of PSGL-1 curtails T cell exhaustion, indicating that PSGL-1 represents an immunotherapeutic target for PD-1-blockade-resistant tumors.

OGT controls mammalian cell viability by regulating the proteasome/mTOR/ mitochondrial axis.

O-GlcNAc transferase (OGT) modifies serine and threonine residues on nuclear and cytosolic proteins with O-linked N-acetylglucosamine (GlcNAc). OGT is essential for mammalian cell viability, but the underlying mechanisms are still enigmatic. We performed a genome-wide CRISPR-Cas9 screen in mouse embryonic stem cells (mESCs) to identify candidates whose depletion rescued the block in cell proliferation induced by OGT deficiency. We show that the block in cell proliferation in OGT-deficient cells stems from mitochondrial dysfunction secondary to mTOR (mechanistic target of rapamycin) hyperactivation. In normal cells, OGT maintains low mTOR activity and mitochondrial fitness through suppression of proteasome activity; in the absence of OGT, increased proteasome activity results in increased steady-state amino acid levels, which in turn promote mTOR lysosomal translocation and activation, and increased oxidative phosphorylation. mTOR activation in OGT-deficient mESCs was confirmed by an independent phospho-proteomic screen. Our study highlights a unique series of events whereby OGT regulates the proteasome/ mTOR/ mitochondrial axis in a manner that maintains homeostasis of intracellular amino acid levels, mitochondrial fitness, and cell viability. A similar mechanism operates in CD8+ T cells, indicating its generality across mammalian cell types. Manipulating OGT activity may have therapeutic potential in diseases in which this signaling pathway is impaired.

Active DNA demethylation damages DNA.

Active DNA demethylation maintains enhancer activity in nonproliferating cells but can damage DNA.

Acute deletion of TET enzymes results in aneuploidy in mouse embryonic stem cells through decreased expression of Khdc3.

TET (Ten-Eleven Translocation) dioxygenases effect DNA demethylation through successive oxidation of the methyl group of 5-methylcytosine (5mC) in DNA. In humans and in mouse models, TET loss-of-function has been linked to DNA damage, genome instability and oncogenesis. Here we show that acute deletion of all three Tet genes, after brief exposure of triple-floxed, Cre-ERT2-expressing mouse embryonic stem cells (mESC) to 4-hydroxytamoxifen, results in chromosome mis-segregation and aneuploidy; moreover, embryos lacking all three TET proteins showed striking variation in blastomere numbers and nuclear morphology at the 8-cell stage. Transcriptional profiling revealed that mRNA encoding a KH-domain protein, Khdc3 (Filia), was downregulated in triple TET-deficient mESC, concomitantly with increased methylation of CpG dinucleotides in the vicinity of the Khdc3 gene. Restoring KHDC3 levels in triple Tet-deficient mESC prevented aneuploidy. Thus, TET proteins regulate Khdc3 gene expression, and TET deficiency results in mitotic infidelity and genome instability in mESC at least partly through decreased expression of KHDC3.

HMCES protects immunoglobulin genes specifically from deletions during somatic hypermutation.

Somatic hypermutation (SHM) produces point mutations in immunoglobulin (Ig) genes in B cells when uracils created by the activation-induced deaminase are processed in a mutagenic manner by enzymes of the base excision repair (BER) and mismatch repair (MMR) pathways. Such uracil processing creates DNA strand breaks and is susceptible to the generation of deleterious deletions. Here, we demonstrate that the DNA repair factor HMCES strongly suppresses deletions without significantly affecting other parameters of SHM in mouse and human B cells, thereby facilitating the production of antigen-specific antibodies. The deletion-prone repair pathway suppressed by HMCES operates downstream from the uracil glycosylase UNG and is mediated by the combined action of BER factor APE2 and MMR factors MSH2, MSH6, and EXO1. HMCES's ability to shield against deletions during SHM requires its capacity to form covalent cross-links with abasic sites, in sharp contrast to its DNA end-joining role in class switch recombination but analogous to its genome-stabilizing role during DNA replication. Our findings lead to a novel model for the protection of Ig gene integrity during SHM in which abasic site cross-linking by HMCES intercedes at a critical juncture during processing of vulnerable gapped DNA intermediates by BER and MMR enzymes.

TET deficiency perturbs mature B cell homeostasis and promotes oncogenesis associated with accumulation of G-quadruplex and R-loop structures.

Enzymes of the TET family are methylcytosine dioxygenases that undergo frequent mutational or functional inactivation in human cancers. Recurrent loss-of-function mutations in TET proteins are frequent in human diffuse large B cell lymphoma (DLBCL). Here, we investigate the role of TET proteins in B cell homeostasis and development of B cell lymphomas with features of DLBCL. We show that deletion of Tet2 and Tet3 genes in mature B cells in mice perturbs B cell homeostasis and results in spontaneous development of germinal center (GC)-derived B cell lymphomas with increased G-quadruplexes and R-loops. At a genome-wide level, G-quadruplexes and R-loops were associated with increased DNA double-strand breaks (DSBs) at immunoglobulin switch regions. Deletion of the DNA methyltransferase DNMT1 in TET-deficient B cells prevented expansion of GC B cells, diminished the accumulation of G-quadruplexes and R-loops and delayed B lymphoma development, consistent with the opposing functions of DNMT and TET enzymes in DNA methylation and demethylation. Clustered regularly interspaced short palindromic repeats (CRISPR)-mediated depletion of nucleases and helicases that regulate G-quadruplexes and R-loops decreased the viability of TET-deficient B cells. Our studies suggest a molecular mechanism by which TET loss of function might predispose to the development of B cell malignancies.

5-Hydroxymethylcytosine-mediated active demethylation is required for mammalian neuronal differentiation and function.

Although high levels of 5-hydroxymethylcytosine (5hmC) accumulate in mammalian neurons, our knowledge of its roles in terminal differentiation or as an intermediate in active DNA demethylation is incomplete. We report high-resolution mapping of DNA methylation and hydroxymethylation, chromatin accessibility, and histone marks in developing postmitotic Purkinje cells (PCs) in Mus musculus. Our data reveal new relationships between PC transcriptional and epigenetic programs, and identify a class of genes that lose both 5-methylcytosine (5mC) and 5hmC during terminal differentiation. Deletion of the 5hmC writers Tet1, Tet2, and Tet3 from postmitotic PCs prevents loss of 5mC and 5hmC in regulatory domains and gene bodies, and hinders transcriptional and epigenetic developmental transitions. Our data demonstrate that Tet-mediated active DNA demethylation occurs in vivo, and that acquisition of the precise molecular properties of adult PCs require continued oxidation of 5mC to 5hmC during the final phases of differentiation.

At birth, the mammalian brain contains tens of billions of neurons. Although the number does not increase much as the animal grows, there are many dramatic changes to their size and structure. These changes allow the neurons to communicate with one another, develop into networks, and learn the tasks of the adult brain. One way that these changes occur is by the accumulation of chemical marks on each neuron's DNA that help dictate which genes switch on, and which turn off. One of the most common ways that DNA can be marked is through the addition of a chemical group called a methyl group to one of the four DNA bases, cytosine. This process is called methylation. When methylation occurs, cytosine becomes 5-methylcytosine, or 5mC for short. In 2009, researchers found another modification present in the DNA in the brain: 5-hydroxymethylcytosine, or 5hmC. This modification appears when a group of proteins called the Tet hydroxylases turn 5mC into 5hmC. Converting 5mC to 5hmC normally helps cells remove marks on their DNA before they divide and expand. This is important because the newly generated cells need to be able to accumulate their own methylation marks to perform their roles properly. However, neurons in the brain accumulate 5hmC after birth, when the cells are no longer dividing, indicating that 5hmC may be required for the neurons to mature. Stoyanova et al. set out to determine whether mouse neurons need 5hmC to get their adult characteristics by tracking the chemical changes that occur in DNA from birth to adulthood. Some of the mice they tested produced 5hmC normally, while others lacked the genes necessary to make the Tet proteins in a specific class of neurons, preventing them from converting 5mC to 5hmC as they differentiate. The results reveal that neurons do not mature properly if 5hmC is not produced continuously following the first week of life. This is because neurons need to have the right genes switched on and off to differentiate correctly, and this only happens when 5hmC accumulates in some genes, while 5hmC and 5mC are removed from others. The data highlight the role of the Tet proteins, which convert 5mC into 5hmC, in preparing the marks for removal and demonstrate that active removal of these marks is essential for neuronal differentiation. Given the role of 5hmC in the development of neurons, it is possible that problems in this system could contribute to brain disorders. Further studies aimed at understanding how cells control 5hmC levels could lead to new ways to improve brain health. Research has also shown that if dividing cells lose the ability to make 5hmC, they can become cancerous. Future work could explain more about how and why this happens.

Nano-optogenetic engineering of CAR T cells for precision immunotherapy with enhanced safety.

Chimeric antigen receptor (CAR) T cell-based immunotherapy, approved by the US Food and Drug Administration, has shown curative potential in patients with haematological malignancies. However, owing to the lack of control over the location and duration of the anti-tumour immune response, CAR T cell therapy still faces safety challenges arising from cytokine release syndrome and on-target, off-tumour toxicity. Herein, we present the design of light-switchable CAR (designated LiCAR) T cells that allow real-time phototunable activation of therapeutic T cells to precisely induce tumour cell killing. When coupled with imaging-guided, surgically removable upconversion nanoplates that have enhanced near-infrared-to-blue upconversion luminescence as miniature deep-tissue photon transducers, LiCAR T cells enable both spatial and temporal control over T cell-mediated anti-tumour therapeutic activity in vivo with greatly mitigated side effects. Our nano-optogenetic immunomodulation platform not only provides a unique approach to interrogate CAR-mediated anti-tumour immunity, but also sets the stage for developing precision medicine to deliver personalized anticancer therapy.

Novel Antibodies for the Simple and Efficient Enrichment of Native O-GlcNAc Modified Peptides.

Antibodies against posttranslational modifications (PTMs) such as lysine acetylation, ubiquitin remnants, or phosphotyrosine have resulted in significant advances in our understanding of the fundamental roles of these PTMs in biology. However, the roles of a number of PTMs remain largely unexplored due to the lack of robust enrichment reagents. The addition of N-acetylglucosamine to serine and threonine residues (O-GlcNAc) by the O-GlcNAc transferase (OGT) is a PTM implicated in numerous biological processes and disease states but with limited techniques for its study. Here, we evaluate a new mixture of anti-O-GlcNAc monoclonal antibodies for the immunoprecipitation of native O-GlcNAcylated peptides from cells and tissues. The anti-O-GlcNAc antibodies display good sensitivity and high specificity toward O-GlcNAc-modified peptides and do not recognize O-GalNAc or GlcNAc in extended glycans. Applying this antibody-based enrichment strategy to synaptosomes from mouse brain tissue samples, we identified over 1300 unique O-GlcNAc-modified peptides and over 1000 sites using just a fraction of sample preparation and instrument time required in other landmark investigations of O-GlcNAcylation. Our rapid and robust method greatly simplifies the analysis of O-GlcNAc signaling and will help to elucidate the role of this challenging PTM in health and disease.

Perceived vulnerability to overdose-related arrests among people who use drugs in Maryland.

BACKGROUND: People who use drugs (PWUD) must weigh complex legal scenarios when seeking help during overdose events. Good Samaritan laws (GSL) offer limited immunity for certain low-level drug crimes to encourage PWUD to call 911. Drug-induced homicide laws (DHL) allow for criminal prosecution of people delivering drugs that result in overdose death and may exert opposing effects on the decision-making process. We examined whether perceptions of these laws were related to overall perceived vulnerability to overdose-related arrests, which can impact help-seeking and overdose mortality. METHODS: We conducted a cross-sectional study of PWUD (N = 173) in Anne Arundel County, Maryland and measured sociodemographic characteristics, structural vulnerabilities, and knowledge of GSL and DHL. Perceived vulnerability to overdose-related arrest was defined as self-reported concern arising from calling 911, receiving medical help, or supplying drugs in the event of an overdose. Multivariable logistic regression was used to identify significant correlates of perceived vulnerability to overdose-related arrest. RESULTS: Most participants were aware of DHL (87%) and half were aware of GSL (53%). Forty-seven percent of PWUD expressed concern about arrest during or due to an overdose. After adjustment, positive correlates of perceived vulnerability to arrest were non-white race (aOR 2.0, 95% CI 1.5-2.5) and hearing of somebody charged with DHL (aOR 3.1, 95%CI 1.9-5.0), and negative correlates were history of drug treatment (aOR 0.6, 95%CI 0.4-1.0), receiving naloxone (aOR 0.6, 95% CI 0.4-1.0), and having made, sold or traded drugs in the past 3 months (aOR 0.4, 95% CI 0.2-0.9). CONCLUSIONS: We report persisting concern about arrest during overdose events among street-based PWUD facing a complicated landscape of legal protections and liabilities. Findings demonstrate clear racial disparities of concern outside an urban centre, where impacts of policing on health are less studied, and present evidence that DHL may compromise overdose prevention efforts. Changes to drug policy and enforcement including police nonattendance at overdose scenes may be necessary to promote help-seeking among PWUD and reduce overdose fatalities.

Whole-genome analysis of TET dioxygenase function in regulatory T cells.

TET methylcytosine dioxygenases are essential for the stability and function of regulatory T cells (Treg cells), which maintain immune homeostasis and self-tolerance and express the lineage-determining transcription factor Foxp3. Here, we use whole-genome analyses to show that the transcriptional program and epigenetic features (DNA modification, chromatin accessibility) of Treg cells are attenuated in the absence of Tet2 and Tet3. Conversely, the addition of the TET activator vitamin C during TGFß-induced iTreg cell differentiation in vitro potentiates the expression of Treg signature genes and alters the epigenetic landscape to better resemble that of Treg cells generated in vivo. Vitamin C enhances IL-2 responsiveness in iTreg cells by increasing IL2Rα expression, STAT5 phosphorylation, and STAT5 binding, mimicking the IL-2/STAT5 dependence of Treg cells generated in vivo. In summary, TET proteins play essential roles in maintaining Treg molecular features and promoting their dependence on IL-2. TET activity during endogenous Treg development and potentiation of TET activity by vitamin C during iTreg differentiation are necessary to maintain the transcriptional and epigenetic features of Treg cells.

BATF and IRF4 cooperate to counter exhaustion in tumor-infiltrating CAR T cells.

The transcription factors nuclear factor of activated T cells (NFAT) and activator protein 1 (AP-1; Fos-Jun) cooperate to promote the effector functions of T cells, but NFAT in the absence of AP-1 imposes a negative feedback program of T cell hyporesponsiveness (exhaustion). Here, we show that basic leucine zipper ATF-like transcription factor (BATF) and interferon regulatory factor 4 (IRF4) cooperate to counter T cell exhaustion in mouse tumor models. Overexpression of BATF in CD8+ T cells expressing a chimeric antigen receptor (CAR) promoted the survival and expansion of tumor-infiltrating CAR T cells, increased the production of effector cytokines, decreased the expression of inhibitory receptors and the exhaustion-associated transcription factor TOX and supported the generation of long-lived memory T cells that controlled tumor recurrence. These responses were dependent on BATF-IRF interaction, since cells expressing a BATF variant unable to interact with IRF4 did not survive in tumors and did not effectively delay tumor growth. BATF may improve the antitumor responses of CAR T cells by skewing their phenotypes and transcriptional profiles away from exhaustion and towards increased effector function.

Roles of TET and TDG in DNA demethylation in proliferating and non-proliferating immune cells.

BACKGROUND: TET enzymes mediate DNA demethylation by oxidizing 5-methylcytosine (5mC) in DNA to 5-hydroxymethylcytosine (5hmC), 5-formylcytosine (5fC), and 5-carboxylcytosine (5caC). Since these oxidized methylcytosines (oxi-mCs) are not recognized by the maintenance methyltransferase DNMT1, DNA demethylation can occur through "passive," replication-dependent dilution when cells divide. A distinct, replication-independent ("active") mechanism of DNA demethylation involves excision of 5fC and 5caC by the DNA repair enzyme thymine DNA glycosylase (TDG), followed by base excision repair. RESULTS: Here by analyzing inducible gene-disrupted mice, we show that DNA demethylation during primary T cell differentiation occurs mainly through passive replication-dependent dilution of all three oxi-mCs, with only a negligible contribution from TDG. In addition, by pyridine borane sequencing (PB-seq), a simple recently developed method that directly maps 5fC/5caC at single-base resolution, we detect the accumulation of 5fC/5caC in TDG-deleted T cells. We also quantify the occurrence of concordant demethylation within and near enhancer regions in the Il4 locus. In an independent system that does not involve cell division, macrophages treated with liposaccharide accumulate 5hmC at enhancers and show altered gene expression without DNA demethylation; loss of TET enzymes disrupts gene expression, but loss of TDG has no effect. We also observe that mice with long-term (1 year) deletion of Tdg are healthy and show normal survival and hematopoiesis. CONCLUSIONS: We have quantified the relative contributions of TET and TDG to cell differentiation and DNA demethylation at representative loci in proliferating T cells. We find that TET enzymes regulate T cell differentiation and DNA demethylation primarily through passive dilution of oxi-mCs. In contrast, while we observe a low level of active, replication-independent DNA demethylation mediated by TDG, this process does not appear to be essential for immune cell activation or differentiation.

DNA Translocation through Vertically Stacked 2D Layers of Graphene and Hexagonal Boron Nitride Heterostructure Nanopore.

Cost-effective, fast, and reliable DNA sequencing can be enabled by advances in nanopore-based methods, such as the use of atomically thin graphene membranes. However, strong interaction of DNA bases with graphene leads to undesirable effects such as sticking of DNA strands to the membrane surface. While surface functionalization is one way to counter this problem, here, we present another solution based on a heterostructure nanopore system, consisting of a monolayer of graphene and hexagonal boron nitride (hBN) each. Molecular dynamics studies of DNA translocation through this heterostructure nanopore revealed a surprising and crucial influence of the heterostructure layer order in controlling the base specific signal variability. Specifically, the heterostructure with graphene on top of hBN had nearly 3-10× lower signal variability than the one with hBN on top of graphene. Simulations point to the role of differential underside sticking of DNA bases as a possible reason for the observed influence of the layer order. Our studies can guide the development of experimental systems to study and exploit DNA translocation through two-dimensional heterostructure nanopores for single molecule sequencing and sensing applications.