DNA N(6)-methyladenine: a new epigenetic mark in eukaryotes?

Serum Folate and Vitamin B12 Modify the Associations of N6AMT1 Genetic Variants with Gestational Diabetes Mellitus: A Cross-Sectional Study in Chinese Pregnant Women

Purpose

This study aimed to explore the association between N-6 adenine-specific DNA methyltransferase 1 (N6AMT1) single nucleotide polymorphisms (SNPs) and gestational diabetes mellitus (GDM) and the modification of the relationship by folate and vitamin B12.

Methods

A cross-sectional study involving 1303 pregnant women (262 GDM and 1041 non-GDM) was performed in Tianjin, China. Nine SNPs in N6AMT1 were genotyped, and serum folate, vitamin B12, and homocysteine (Hcy) levels were measured. The logistic regression models determined the odds ratios (ORs) for SNPs in N6AMT1 and the gene-nutrition interactions on GDM.

Results

N6AMT1 rs7282280, rs1048546, and rs1997605 were related to GDM under the dominant model after adjusting for multiple covariates. Individuals carrying the N6AMT1 rs7282280 TC/TT genotypes had a lower risk of developing GDM, regardless of serum folate and vitamin B12 levels. However, rs1048546 TG/GG genotypes were associated with lower GDM risk when serum folate ≥ 6.0 ng/mL. Pregnancies with the risk genotypes in N6AMT1 and higher serum folate or lower vitamin B12 are more prone to GDM. The study also showed a statistically significant additive interaction between N6AMT1 rs1997605 GG genotypes and lower vitamin B12 (RERI: 2.54; 95% CI: 0.17, 4.92).

Conclusion

SNPs in N6AMT1 were found to be associated with GDM, and serum folate and vitamin B12 levels can modify their associations.

Targeted DNA N6-methyladenine editing by dCas9 fused to METTL4 in the lepidopteran model insect Bombyx mori

We have established a novel CRISPR-dCas9-METTL4 epigenome editing tool that can methylate target regions to achieve site-specific DNA 6mA methylation in both hypermethylated and hypomethylated genes. Targeted methylation on genes by dCas9-METTL4 results in misexpression, allowing for the functional investigation of target genes of interest in silkworm.

Identification and quantification of N6-methyladenosine by chemical derivatization coupled with 19F NMR spectroscopy

N 6-Methyladenosine (6mA) is a well-known prokaryotic DNA modification that has been shown to play epigenetic roles in eukaryotic DNA. Accurate detection and quantification of 6mA are prerequisites for molecular understanding of the impact of 6mA modification on DNA. However, the existing methods have several problems, such as high false-positive rate, time-consuming and complex operating procedures. Chemical sensors for the selective detection of 6mA modification are rarely reported in the literature. Fluorinated phenylboronic acid combined with 19F NMR analysis is an effective method for determining DNA or RNA modification. In this study, we presented a simple and fast chemical method for labelling the 6th imino group of 6mA using a boric-acid-derived probe. Besides, the trifluoromethyl group of trifluoromethyl phenylboronic acid (2a) could detect 6mA modification through 19F NMR. Combined with this sensor system, 6mA modification could be detected well and quickly in 6 types of deoxynucleoside mixtures and DNA samples. Taken together, the method developed in the current study has potential for specific detection of 6mA in biological samples.

4mCPred-GSIMP: Predicting DNA N4-methylcytosine sites in the mouse genome with multi-Scale adaptive features extraction and fusion

The epigenetic modification of DNA N4-methylcytosine (4mC) is vital for controlling DNA replication and expression. It is crucial to pinpoint 4mC's location to comprehend its role in physiological and pathological processes. However, accurate 4mC detection is difficult to achieve due to technical constraints. In this paper, we propose a deep learning-based approach 4mCPred-GSIMP for predicting 4mC sites in the mouse genome. The approach encodes DNA sequences using four feature encoding methods and combines multi-scale convolution and improved selective kernel convolution to adaptively extract and fuse features from different scales, thereby improving feature representation and optimization effect. In addition, we also use convolutional residual connections, global response normalization and pointwise convolution techniques to optimize the model. On the independent test dataset, 4mCPred-GSIMP shows high sensitivity, specificity, accuracy, Matthews correlation coefficient and area under the curve, which are 0.7812, 0.9312, 0.8562, 0.7207 and 0.9233, respectively. Various experiments demonstrate that 4mCPred-GSIMP outperforms existing prediction tools.

Lactate-induced protein lactylation: A bridge between epigenetics and metabolic reprogramming in cancer

Lactate is not only an endpoint of glycolysis but is gradually being discovered to play the role of a universal metabolic fuel for energy via the 'lactate shuttle' moving between cells and transmitting signals. The glycolytic-dependent metabolism found in tumours and fast-growing cells has made lactate a pivotal player in energy metabolism reprogramming, which enables cells to obtain abundant energy in a short time. Moreover, lactate can provide favourable conditions for tumorigenesis by shaping the acidic tumour microenvironment, recruiting immune cells, etc. and the recently discovered lactate-induced lactylation moves even further on pro-tumorigenesis mechanisms of lactate production, circulation and utilization. As with other epigenetic modifications, lactylation can modify histone proteins to alter the spatial configuration of chromatin, affect DNA accessibility and regulate the expression of corresponding genes. What's more, the degree of lactylation is inseparable from the spatialized lactate concentration, which builds a bridge between epigenetics and metabolic reprogramming. Here, we review the important role of lactate in energy reprogramming, summarize the latest finding of lactylation in tumorigenesis and try to explore therapeutic strategies in oncotherapy that can kill two birds with one stone.

Comprehensive analysis unveils altered binding kinetics of 5-/6-methylCytosine/adenine modifications in R2R3-DNA system

Recent studies have shown that DNA methylation is an important epigenetic marker. Two prominent forms are methylation of the C5 position of cytosine and methylation of the C6 position of adenine. Given the vital significance of DNA methylation, investigating the mechanisms that influence protein binding remains a compelling pursuit. This study used molecular dynamics simulations to investigate the binding patterns of R2R3 protein and four differentially methylated DNAs. The alanine scanning combined with interaction entropy method was used to identify key residues that respond to different methylation patterns. The order of protein binding ability to DNA is as follows: unmethylated DNA > A11 methylation (5'-A6mAC-3') (6m2A system) > A10 methylation (5'-6mAAC-3') (6m1A system) > both A10 and A11 methylation (5'-6mA6mAC-3') (6mAA system) > C12 methylation (5'-AA5mC-3') (5mC system). All methylation systems lead to the sixth α helix (H6) (residues D105 to L116) moving away from the binding interface, and in the 5mC and 6m1A systems, the third α helix (H3) (residues G54 to L65) exhibits a similar trend. When the positively charged amino acids in H3 and H6 move away from the binding interface, their electrostatic and van der Waals interactions with the negatively charged DNA are weakened. Structural changes induced by methylation contributed to the destabilization of the hydrogen bond network near the original binding site, except for the 6m2A system. Moreover, there is a positive correlation between the number of methylated sites and the probability of distorting the DNA structure. Our study explores how different methylation patterns affect binding and structural adaptability, and have implications for drug discovery and understanding diseases related to abnormal methylation.

AamA-mediated epigenetic control of genome-wide gene expression and phenotypic traits in Acinetobacter baumannii ATCC 17978

Individual deletions of three genes encoding orphan DNA methyltransferases resulted in the occurrence of growth defect only in the aamA (encoding AcinetobacterAdenine Methylase A) mutant of A. baumannii strain ATCC 17978. Our single-molecule real-time sequencing-based methylome analysis revealed multiple AamA-mediated DNA methylation sites and proposed a potent census target motif (TTTRAATTYAAA). Loss of Dam led to modulation of genome-wide gene expression, and several Dam-target sites including the promoter region of the trmD operon (rpsP, rimM, trmD, and rplS) were identified through our methylome and transcriptome analyses. AamA methylation also appeared to control the expression of many genes linked to membrane functions (lolAB, lpxO), replication (dnaA) and protein synthesis (trmD operon) in the strain ATCC 17978. Interestingly, cellular resistance against several antibiotics and ethidium bromide through functions of efflux pumps diminished in the absence of the aamA gene, and the complementation of aamA gene restored the wild-type phenotypes. Other tested phenotypic traits such as outer-membrane vesicle production, biofilm formation and virulence were also affected in the aamA mutant. Collectively, our data indicated that epigenetic regulation through AamA-mediated DNA methylation of novel target sites mostly in the regulatory regions could contribute significantly to changes in multiple phenotypic traits in A. baumannii ATCC 17978.

Prediction of DNA Methylation based on Multi-dimensional feature encoding and double convolutional fully connected convolutional neural network

DNA methylation takes on critical significance to the regulation of gene expression by affecting the stability of DNA and changing the structure of chromosomes. DNA methylation modification sites should be identified, which lays a solid basis for gaining more insights into their biological functions. Existing machine learning-based methods of predicting DNA methylation have not fully exploited the hidden multidimensional information in DNA gene sequences, such that the prediction accuracy of models is significantly limited. Besides, most models have been built in terms of a single methylation type. To address the above-mentioned issues, a deep learning-based method was proposed in this study for DNA methylation site prediction, termed the MEDCNN model. The MEDCNN model is capable of extracting feature information from gene sequences in three dimensions (i.e., positional information, biological information, and chemical information). Moreover, the proposed method employs a convolutional neural network model with double convolutional layers and double fully connected layers while iteratively updating the gradient descent algorithm using the cross-entropy loss function to increase the prediction accuracy of the model. Besides, the MEDCNN model can predict different types of DNA methylation sites. As indicated by the experimental results,the deep learning method based on coding from multiple dimensions outperformed single coding methods, and the MEDCNN model was highly applicable and outperformed existing models in predicting DNA methylation between different species. As revealed by the above-described findings, the MEDCNN model can be effective in predicting DNA methylation sites.

Shaping eukaryotic epigenetic systems by horizontal gene transfer

DNA methylation constitutes one of the pillars of epigenetics, relying on covalent bonds for addition and/or removal of chemically distinct marks within the major groove of the double helix. DNA methyltransferases, enzymes which introduce methyl marks, initially evolved in prokaryotes as components of restriction-modification systems protecting host genomes from bacteriophages and other invading foreign DNA. In early eukaryotic evolution, DNA methyltransferases were horizontally transferred from bacteria into eukaryotes several times and independently co-opted into epigenetic regulatory systems, primarily via establishing connections with the chromatin environment. While C5-methylcytosine is the cornerstone of plant and animal epigenetics and has been investigated in much detail, the epigenetic role of other methylated bases is less clear. The recent addition of N4-methylcytosine of bacterial origin as a metazoan DNA modification highlights the prerequisites for foreign gene co-option into the host regulatory networks, and challenges the existing paradigms concerning the origin and evolution of eukaryotic regulatory systems.

Potential role of N6-adenine DNA methylation in alternative splicing and endosymbiosis in Paramecium bursaria

N⁶-adenine DNA methylation (6mA), a rediscovered epigenetic mark in eukaryotic organisms, diversifies in abundance, distribution, and function across species, necessitating its study in more taxa. Paramecium bursaria is a typical model organism with endosymbiotic algae of the species Chlorella variabilis. This consortium therefore serves as a valuable system to investigate the functional role of 6mA in endosymbiosis, as well as the evolutionary importance of 6mA among eukaryotes. In this study, we report the first genome-wide, base pair-resolution map of 6mA in P. bursaria and identify its methyltransferase PbAMT1. Functionally, 6mA exhibits a bimodal distribution at the 5' end of RNA polymerase II-transcribed genes and possibly participates in transcription by facilitating alternative splicing. Evolutionarily, 6mA co-evolves with gene age and likely serves as a reverse mark of endosymbiosis-related genes. Our results offer new insights for the functional diversification of 6mA in eukaryotes as an important epigenetic mark.

6mA DNA Methylation on Genes in Plants Is Associated with Gene Complexity, Expression and Duplication

N6-methyladenine (6mA) DNA methylation has emerged as an important epigenetic modification in eukaryotes. Nevertheless, the evolution of the 6mA methylation of homologous genes after species and after gene duplications remains unclear in plants. To understand the evolution of 6mA methylation, we detected the genome-wide 6mA methylation patterns of four lotus plants (Nelumbo nucifera) from different geographic origins by nanopore sequencing and compared them to patterns in Arabidopsis and rice. Within lotus, the genomic distributions of 6mA sites are different from the widely studied 5mC methylation sites. Consistently, in lotus, Arabidopsis and rice, 6mA sites are enriched around transcriptional start sites, positively correlated with gene expression levels, and preferentially retained in highly and broadly expressed orthologs with longer gene lengths and more exons. Among different duplicate genes, 6mA methylation is significantly more enriched and conserved in whole-genome duplicates than in local duplicates. Overall, our study reveals the convergent patterns of 6mA methylation evolution based on both lineage and duplicate gene divergence, which underpin their potential role in gene regulatory evolution in plants.

Advances in Protozoan Epigenetic Targets and Their Inhibitors for the Development of New Potential Drugs

Protozoan parasite diseases cause significant mortality and morbidity worldwide. Factors such as climate change, extreme poverty, migration, and a lack of life opportunities lead to the propagation of diseases classified as tropical or non-endemic. Although there are several drugs to combat parasitic diseases, strains resistant to routinely used drugs have been reported. In addition, many first-line drugs have adverse effects ranging from mild to severe, including potential carcinogenic effects. Therefore, new lead compounds are needed to combat these parasites. Although little has been studied regarding the epigenetic mechanisms in lower eukaryotes, it is believed that epigenetics plays an essential role in vital aspects of the organism, from controlling the life cycle to the expression of genes involved in pathogenicity. Therefore, using epigenetic targets to combat these parasites is foreseen as an area with great potential for development. This review summarizes the main known epigenetic mechanisms and their potential as therapeutics for a group of medically important protozoal parasites. Different epigenetic mechanisms are discussed, highlighting those that can be used for drug repositioning, such as histone post-translational modifications (HPTMs). Exclusive parasite targets are also emphasized, including the base J and DNA 6 mA. These two categories have the greatest potential for developing drugs to treat or eradicate these diseases.

The N6-methyladenine DNA demethylase ALKBH1 promotes gastric carcinogenesis by disrupting NRF1 binding capacity

DNA N6-methyladenine (6mA) is an epigenetic modification that regulates various biological processes. Here, we show that gastric cancer (GC) cells and tumors display a marked reduction in 6mA levels compared with normal gastric tissues and cells. 6mA is abundant in the surrounding transcription start sites and occurs at consensus motifs. Among the 6mA regulators, ALKBH1, a demethylase, is significantly overexpressed in GC tissues compared with adjacent normal tissues. Moreover, high ALKBH1 expression is associated with poor survival of patients with GC. ALKBH1 knockout in mice impairs chemically induced gastric carcinogenesis. Mechanistically, ALKBH1 mediates DNA 6mA demethylation to repress gene expression. In particular, the 6mA sites are enriched in NRF1 binding sequences and targeted for demethylation by ALKBH1. ALKBH1-induced 6mA demethylation inhibits NRF1-driven transcription of downstream targets, including multiple genes involved in the AMP-activated protein kinase (AMPK) signaling pathway. Accordingly, ALKBH1 suppresses AMPK signaling, causing a metabolic shift toward the Warburg effect, which facilitates tumorigenesis.

m6A-mediated nonhomologous end joining (NHEJ) pathway regulates senescence in Brachionus plicatilis (Rotifera)

Epigenetic modifications play an important role in the regulation of senescence. N6-methyladenosine (m6A) is the most abundant modification of mRNA. However, the impact of m6A on senescence remains largely unknown at the animal individual level. Standard model organisms Caenorhabditis elegans and Drosophila melanogaster lack many gene homologs of vertebrate m6A system that are present in other invertebrates. In this study, we employed a small aquatic invertebrate Brachionus plicatilis which has been used in aging studies for nearly 100 years to study how m6A affects aging. Phylogenetic analysis confirmed that rotifers' m6A pathway has a conserved methyltransferase complex but no demethylases and the m6A reading system was more akin to that of vertebrates than that of D. melanogaster. m6A methyltransferases are highly expressed during development but reduces dramatically during aging. Knockdown of METTL3 results in decreased fecundity and premature senescence of rotifers. Furthermore, RT-qPCR analysis indicates a role for m6A in the nonhomologous end joining (NHEJ) pathway of DNA double-strand breaks (DSBs) repair. Altogether, our work reveals a senescence regulatory model for the rotifer METTL3-m6A-NHEJ pathway.

Long range inter-chromosomal interaction of Oct4 distal enhancer loci regulates ESCs pluripotency

Nuclear architecture underlies the transcriptional programs within the cell to establish cell identity. As previously demonstrated, long-range chromatin interactions of the Oct4 distal enhancer (DE) are correlated with active transcription in naïve state embryonic stem cells. Here, we identify and characterize extreme long-range interactions of the Oct4 DE through a novel CRISPR labeling technique we developed and chromosome conformation capture to identify lethal giant larvae 2 (Llgl2) and growth factor receptor-bound protein 7 (Grb7) as putative functional interacting target genes in different chromosomes. We show that the Oct4 DE directly regulates expression of Llgl2 and Grb7 in addition to Oct4. Expression of Llgl2 and Grb7 closely correlates with the pluripotent state, where knock down of either result in loss of pluripotency, and overexpression enhances somatic cell reprogramming. We demonstrated that biologically important interactions of the Oct4 DE can occur at extreme distances that are necessary for the maintenance of the pluripotent state.

I-DNAN6mA: Accurate Identification of DNA N6-Methyladenine Sites Using the Base-Pairing Map and Deep Learning

The recent discovery of numerous DNA N⁶-methyladenine (6mA) sites has transformed our perception about the roles of 6mA in living organisms. However, our ability to understand them is hampered by our inability to identify 6mA sites rapidly and cost-efficiently by existing experimental methods. Developing a novel method to quickly and accurately identify 6mA sites is critical for speeding up the progress of its function detection and understanding. In this study, we propose a novel computational method, called I-DNAN6mA, to identify 6mA sites and complement experimental methods well, by leveraging the base-pairing rules and a well-designed three-stage deep learning model with pairwise inputs. The performance of our proposed method is benchmarked and evaluated on four species, i.e., Arabidopsis thaliana, Drosophila melanogaster, Rice, and Rosaceae. The experimental results demonstrate that I-DNAN6mA achieves area under the receiver operating characteristic curve values of 0.967, 0.963, 0.947, 0.976, and 0.990, accuracies of 91.5, 92.7, 88.2, 0.938, and 96.2%, and Mathew's correlation coefficient values of 0.855, 0.831, 0.763, 0.877, and 0.924 on five benchmark data sets, respectively, and outperforms several existing state-of-the-art methods. To our knowledge, I-DNAN6mA is the first approach to identify 6mA sites using a novel image-like representation of DNA sequences and a deep learning model with pairwise inputs. I-DNAN6mA is expected to be useful for locating functional regions of DNA.

Structural insights into DNA N6-adenine methylation by the MTA1 complex

N⁶-methyldeoxyadenine (6mA) has recently been reported as a prevalent DNA modification in eukaryotes. The Tetrahymena thermophila MTA1 complex consisting of four subunits, namely MTA1, MTA9, p1, and p2, is the first identified eukaryotic 6mA methyltransferase (MTase) complex. Unlike the prokaryotic 6mA MTases which have been biochemically and structurally characterized, the operation mode of the MTA1 complex remains largely elusive. Here, we report the cryogenic electron microscopy structures of the quaternary MTA1 complex in S-adenosyl methionine (SAM)-bound (2.6 Å) and S-adenosyl homocysteine (SAH)-bound (2.8 Å) states. Using an AI-empowered integrative approach based on AlphaFold prediction and chemical cross-linking mass spectrometry, we further modeled a near-complete structure of the quaternary complex. Coupled with biochemical characterization, we revealed that MTA1 serves as the catalytic core, MTA1, MTA9, and p1 likely accommodate the substrate DNA, and p2 may facilitate the stabilization of MTA1. These results together offer insights into the molecular mechanism underpinning methylation by the MTA1 complex and the potential diversification of MTases for N⁶-adenine methylation.

A review of methods for predicting DNA N6-methyladenine sites

Deoxyribonucleic acid(DNA) N6-methyladenine plays a vital role in various biological processes, and the accurate identification of its site can provide a more comprehensive understanding of its biological effects. There are several methods for 6mA site prediction. With the continuous development of technology, traditional techniques with the high costs and low efficiencies are gradually being replaced by computer methods. Computer methods that are widely used can be divided into two categories: traditional machine learning and deep learning methods. We first list some existing experimental methods for predicting the 6mA site, then analyze the general process from sequence input to results in computer methods and review existing model architectures. Finally, the results were summarized and compared to facilitate subsequent researchers in choosing the most suitable method for their work.

High-precision mapping reveals rare N6-deoxyadenosine methylation in the mammalian genome

N⁶-deoxyadenosine methylation (6mA) is the most widespread type of DNA modification in prokaryotes and is also abundantly distributed in some unicellular eukaryotes. However, 6mA levels are remarkably low in mammals. The lack of a precise and comprehensive mapping method has hindered more advanced investigations of 6mA. Here, we report a new method MM-seq (modification-induced mismatch sequencing) for genome-wide 6mA mapping based on a novel detection principle. We found that modified DNA bases are prone to form a local open region that allows capture by antibody, for example, via a DNA breathing or base-flipping mechanism. Specified endonuclease or exonuclease can recognize the antibody-stabilized mismatch-like structure and mark the exact modified sites for sequencing readout. Using this method, we examined the genomic positions of 6mA in bacteria (E. coli), green algae (C. reinhardtii), and mammalian cells (HEK239T, Huh7, and HeLa cells). In contrast to bacteria and green algae, human cells possess a very limited number of 6mA sites which are sporadically distributed across the genome of different cell types. After knocking out the RNA m⁶A methyltransferase METTL3 in mouse ES cells, 6mA becomes mostly diminished. Our results imply that rare 6mA in the mammalian genome is introduced by RNA m⁶A machinery via a non-targeted mechanism.

Hyperactive DNA Cutting for Unbiased UHPLC-MS/MS Quantification of Epigenetic DNA Marks by Engineering DNase I Mutants

Epigenetic DNA modifications, such as 5-methylcytosine, 5-hydroxymethylcytosine, and 5-formylcytosine, are associated with a variety of diseases and potential biomarkers for cancer diagnosis and therapy. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) assays are considered to be the gold standard for qualitative and quantitative detection of DNA modifications. DNA digestion for converting long DNA polymer into 2'-deoxynucleosides is an important preprocessing step to achieve sensitive and accurate LC-MS/MS quantification. Here, we showed that, as stimulated by divalent metal ions, Mg²⁺ and Mn²⁺, the engineered human DNase I Q9R:E13R:N74K mutant can efficiently digest DNA in the presence of monovalent metal ions at a high concentration (e.g., 1 M NaCl), showing hyperactivity on DNA cutting. We also found that the engineered DNase I mutants display exceptional DNA-cutting activity over a wider pH range (5.5-9.5). Due to their hyperactivity and high salt tolerance, the engineered DNase I mutants cut DNA 5mC and dC efficiently. Benefitting from this DNA-cutting hyperactivity, we demonstrated an LC-MS/MS assay for unbiased and accurate quantification of DNA 5mC.

Light Dependent Changes in Adenylate Methylation of the Promoter of the Mitochondrial Citrate Synthase Gene in Maize (Zea mays L.) Leaves

Limited methyl-specific restriction of genomic DNA by endonuclease MAL1 revealed the changes in its methyl status caused by adenine modification in maize (Zea mays L.) leaves under different light conditions (dark, light, irradiation by red and far-red light). Incubation in the light and irradiation by red light exhibited an activating effect on DNA adenine methylase activity, which was reflected in an increase in the number of methylated adenines in GATC sites. Far-red light and darkness exhibited an opposite effect. The use of nitrite conversion of DNA followed by methyladenine-dependent restriction by MboI nuclease revealed a phytochrome B-dependent mechanism of regulation of the methyl status of adenine in the GATC sites in the promoter of the gene encoding the mitochondrial isoform of citrate synthase. Irradiation of plants with red light caused changes in the adenine methyl status of the analyzed amplicon, as evidenced by the presence of restriction products of 290, 254, and 121 nucleotides. Adenine methylation occurred at all three GATC sites in the analyzed DNA sequence. It is concluded that adenylate methylation is controlled by phytochrome B via the transcription factor PIF4 and represents an important mechanism for the tricarboxylic acid cycle regulation by light.

ALKBH4 Stabilization Is Required for Arsenic-Induced 6mA DNA Methylation Inhibition, Keratinocyte Malignant Transformation, and Tumorigenicity

Inorganic arsenic is one of the well-known human skin carcinogens. However, the molecular mechanism by which arsenic promotes carcinogenesis remains unclear. Previous studies have established that epigenetic changes, including changes in DNA methylation, are among the critical mechanisms that drive carcinogenesis. N6-methyladenine (6mA) methylation on DNA is a widespread epigenetic modification that was initially found on bacterial and phage DNA. Only recently has 6mA been identified in mammalian genomes. However, the function of 6mA in gene expression and cancer development is not well understood. Here, we show that chronic low doses of arsenic induce malignant transformation and tumorigenesis in keratinocytes and lead to the upregulation of ALKBH4 and downregulation of 6mA on DNA. We found that reduced 6mA levels in response to low levels of arsenic were mediated by the upregulation of the 6mA DNA demethylase ALKBH4. Moreover, we found that arsenic increased ALKBH4 protein levels and that ALKBH4 deletion impaired arsenic-induced tumorigenicity in vitro and in mice. Mechanistically, we found that arsenic promoted ALKBH4 protein stability through reduced autophagy. Together, our findings reveal that the DNA 6mA demethylaseALKBH4 promotes arsenic tumorigenicity and establishes ALKBH4 as a promising target for arsenic-induced tumorigenesis.

i6mA-Caps: a CapsuleNet-based framework for identifying DNA N6-methyladenine sites

MOTIVATION

DNA N6-methyladenine (6mA) has been demonstrated to have an essential function in epigenetic modification in eukaryotic species in recent research. 6mA has been linked to various biological processes. It's critical to create a new algorithm that can rapidly and reliably detect 6mA sites in genomes to investigate their biological roles. The identification of 6mA marks in the genome is the first and most important step in understanding the underlying molecular processes, as well as their regulatory functions.

RESULTS

In this article, we proposed a novel computational tool called i6mA-Caps which CapsuleNet based a framework for identifying the DNA N6-methyladenine sites. The proposed framework uses a single encoding scheme for numerical representation of the DNA sequence. The numerical data is then used by the set of convolution layers to extract low-level features. These features are then used by the capsule network to extract intermediate-level and later high-level features to classify the 6mA sites. The proposed network is evaluated on three datasets belonging to three genomes which are Rosaceae, Rice and Arabidopsis thaliana. Proposed method has attained an accuracy of 96.71%, 94% and 86.83% for independent Rosaceae dataset, Rice dataset and A.thaliana dataset respectively. The proposed framework has exhibited improved results when compared with the existing top-of-the-line methods.

AVAILABILITY AND IMPLEMENTATION

A user-friendly web-server is made available for the biological experts which can be accessed at: http://nsclbio.jbnu.ac.kr/tools/i6mA-Caps/.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Next-Generation Sequencing-Based Analysis of the Effects of N1- and N6-Methyldeoxyadenosine Adducts on DNA Transcription

DNA methylation can occur naturally or be induced by various environmental and chemotherapeutic agents. The regioisomeric N¹- and N⁶-methyldeoxyadenosine (1mdA and 6mdA, respectively) represent an important class of methylated DNA adducts. In this study, we developed a shuttle vector- and next-generation sequencing-based assay to quantitatively assess the effects of 1mdA and 6mdA on the accuracy and efficiency of DNA transcription. Our results revealed that 1mdA can induce multiple types of mutant transcripts and strongly inhibit DNA transcription, whereas 6mdA is a nonmutagenic DNA adduct that can exhibit a subtle but significant inhibitory effect on DNA transcription in vitro and in human cells. Moreover, our results demonstrated that the transcription-coupled nucleotide excision repair pathway is dispensable for the removal of 1mdA and 6mdA from the template DNA strand in human cells. These findings provided new important insights into the functional interplay between DNA methylation modifications and transcription in mammalian cells.

Hyb4mC: a hybrid DNA2vec-based model for DNA N4-methylcytosine sites prediction

BACKGROUND

DNA N4-methylcytosine is part of the restrictive modification system, which works by regulating some biological processes, for example, the initiation of DNA replication, mismatch repair and inactivation of transposon. However, using experimental methods to detect 4mC sites is time-consuming and expensive. Besides, considering the huge differences in the number of 4mC samples among different species, it is challenging to achieve a robust multi-species 4mC site prediction performance. Hence, it is of great significance to develop effective computational tools to identify 4mC sites.

RESULTS

This work proposes a flexible deep learning-based framework to predict 4mC sites, called Hyb4mC. Hyb4mC adopts the DNA2vec method for sequence embedding, which captures more efficient and comprehensive information compared with the sequence-based feature method. Then, two different subnets are used for further analysis: Hyb_Caps and Hyb_Conv. Hyb_Caps is composed of a capsule neural network and can generalize from fewer samples. Hyb_Conv combines the attention mechanism with a text convolutional neural network for further feature learning.

CONCLUSIONS

Extensive benchmark tests have shown that Hyb4mC can significantly enhance the performance of predicting 4mC sites compared with the recently proposed methods.

Same modification, different location: the mythical role of N6-adenine methylation in plant genomes

The present review summarizes recent advances in the understanding of 6mA in DNA as an emergent epigenetic mark with distinctive characteristics, discusses its importance in plant genomes, and highlights its chemical nature and functions. Adenine methylation is an epigenetic modification present in DNA (6mA) and RNA (m6A) that has a regulatory function in many cellular processes. This modification occurs through a reversible reaction that covalently binds a methyl group, usually at the N⁶ position of the purine ring. This modification carries biophysical properties that affect the stability of nucleic acids as well as their binding affinity with other molecules. DNA 6mA has been related to genome stability, gene expression, DNA replication, and repair mechanisms. Recent advances have shown that 6mA in plant genomes is related to development and stress response. In this review, we present recent advances in the understanding of 6mA in DNA as an emergent epigenetic mark with distinctive characteristics. We discuss the key elements of this modification, focusing mainly on its importance in plant genomes. Furthermore, we highlight its chemical nature and the regulatory effects that it exerts on gene expression and plant development. Finally, we emphasize the functions of 6mA in photosynthesis, stress, and flowering.

Genome-wide DNA N6-adenine methylation in sea buckthorn (Hippophae rhamnoides L.) fruit development

As a new epigenetic mark, DNA N6-adenine (6mA) methylation plays an important role in various biological processes and has been reported in many prokaryotic organisms in recent years. However, the distribution patterns and functions of DNA 6mA modification have been poorly studied in non-model crops. In this study, we observed that the methylation ratio of 6mA was about 0.016% in the sea buckthorn (Hippophae rhamnoides L.) genome using mass spectrometry. We first constructed a comprehensive 6mA landscape in sea buckthorn genome using nanopore sequencing at single-base resolution. Distribution analysis suggested that 6mA methylated sites were widely distributed in the sea buckthorn chromosomes, which were similar to those in Arabidopsis and rice. Furthermore, reduced 6mA DNA methylation is associated with different expression of genes related to the fruit-ripening process in sea buckthorn. Our results revealed that 6mA DNA modification could be considered an important epigenomic mark and contributes to the fruit ripening process in plants.

A fungal dioxygenase CcTet serves as a eukaryotic 6mA demethylase on duplex DNA

N⁶-methyladenosine (6mA) is a DNA modification that has recently been found to play regulatory roles during mammalian early embryo development and mitochondrial transcription. We found that a dioxygenase CcTet from the fungus Coprinopsis cinerea is also a dsDNA 6mA demethylase. It oxidizes 6mA to the intermediate N⁶-hydroxymethyladenosine (6hmA) with robust activity of 6mA-containing duplex DNA (dsDNA) as well as isolated genomics DNA. Structural characterization revealed that CcTet utilizes three flexible loop regions and two key residues-D337 and G331-in the active pocket to preferentially recognize substrates on dsDNA. A CcTet D337F mutant protein retained the catalytic activity on 6mA but lost activity on 5-methylcytosine. Our findings uncovered a 6mA demethylase that works on dsDNA, suggesting potential 6mA demethylation in fungi and elucidating 6mA recognition and the catalytic mechanism of CcTet. The CcTet D337F mutant protein also provides a chemical biology tool for future functional manipulation of DNA 6mA in vivo.

DNA N6-Adenine methylation in HBV-related hepatocellular carcinoma

DNA methylation on N6-adenine (6mA) has recently been found to be a potential epigenetic marker in prokaryotes and eukaryotes. However, its distribution patterns and potential functions in human tumorigenesis remain largely unknown. Here, we reported global profiling of 6mA sites in the genome of hepatocellular carcinoma at single-nucleotide resolution using Nanopore sequencing. 6mA was widely distributed throughout the human genome. The 6mA sites were related to the porphyrin and chlorophyll metabolism in autosomes and were related to oxidative phosphorylation and ATP metabolism in mitochondria. AGG was the most significant motif associated with 6mA modification and the prevalent motifs in tumors were mainly distributed in mitochondria. The density of 6mA was related to the activation of gene transcription and 6mA density in repetitive sequences decreased in hepatocellular carcinoma. DNA 6mA methylation modification may also be a potential biomarker for cancer diagnosis and treatment.

DNA N6-methyldeoxyadenosine in mammals and human disease

N⁶-methyladenine (6mA) is the most prevalent DNA modification in prokaryotes. However, its presence and significance in eukaryotes remain elusive. Recently, with methodology advances in detection and sequencing of 6mA in eukaryotes, 6mA is back in the spotlight. Although multiple studies have reported that 6mA is an important epigenetic mark in eukaryotes and plays a regulatory role in DNA transcription, transposon activation, stress response, and other bioprocesses, there are some discrepancies in the current literature. We review the recent advances in 6mA research in eukaryotes, especially in mammals. In particular, we describe the abundance/distribution of 6mA, its potential role in regulating gene expression, identified regulators, and pathological roles in human diseases, especially in cancer. The limitations faced by the field and future perspectives in 6mA research are also discussed.

Deep6mAPred: A CNN and Bi-LSTM-based deep learning method for predicting DNA N6-methyladenosine sites across plant species

DNA N6-methyladenine (6mA) is a key DNA modification, which plays versatile roles in the cellular processes, including regulation of gene expression, DNA repair, and DNA replication. DNA 6mA is closely associated with many diseases in the mammals and with growth as well as development of plants. Precisely detecting DNA 6mA sites is of great importance to exploration of 6mA functions. Although many computational methods have been presented for DNA 6mA prediction, there is still a wide gap in the practical application. We presented a convolution neural network (CNN) and bi-directional long-short term memory (Bi-LSTM)-based deep learning method (Deep6mAPred) for predicting DNA 6mA sites across plant species. The Deep6mAPred stacked the CNNs and the Bi-LSTMs in a paralleling manner instead of a series-connection manner. The Deep6mAPred also employed the attention mechanism for improving the representations of sequences. The Deep6mAPred reached an accuracy of 0.9556 over the independent rice dataset, far outperforming the state-of-the-art methods. The tests across plant species showed that the Deep6mAPred is of a remarkable advantage over the state of the art methods. We developed a user-friendly web application for DNA 6mA prediction, which is freely available at http://106.13.196.152:7001/ for all the scientific researchers. The Deep6mAPred would enrich tools to predict DNA 6mA sites and speed up the exploration of DNA modification.

MGF6mARice: prediction of DNA N6-methyladenine sites in rice by exploiting molecular graph feature and residual block

DNA N6-methyladenine (6mA) is produced by the N6 position of the adenine being methylated, which occurs at the molecular level, and is involved in numerous vital biological processes in the rice genome. Given the shortcomings of biological experiments, researchers have developed many computational methods to predict 6mA sites and achieved good performance. However, the existing methods do not consider the occurrence mechanism of 6mA to extract features from the molecular structure. In this paper, a novel deep learning method is proposed by devising DNA molecular graph feature and residual block structure for 6mA sites prediction in rice, named MGF6mARice. Firstly, the DNA sequence is changed into a simplified molecular input line entry system (SMILES) format, which reflects chemical molecular structure. Secondly, for the molecular structure data, we construct the DNA molecular graph feature based on the principle of graph convolutional network. Then, the residual block is designed to extract higher level, distinguishable features from molecular graph features. Finally, the prediction module is used to obtain the result of whether it is a 6mA site. By means of 10-fold cross-validation, MGF6mARice outperforms the state-of-the-art approaches. Multiple experiments have shown that the molecular graph feature and residual block can promote the performance of MGF6mARice in 6mA prediction. To the best of our knowledge, it is the first time to derive a feature of DNA sequence by considering the chemical molecular structure. We hope that MGF6mARice will be helpful for researchers to analyze 6mA sites in rice.

Reducing N6AMT1-mediated 6mA DNA modification promotes breast tumor progression via transcriptional repressing cell cycle inhibitors

DNA N6-methyladenosine (6mA) is a novel epigenetic signaling modification in humans and has been implicated in the progression and tumorigenesis of several cancers. However, the function and mechanism of 6mA in breast cancer (BC), the most common cancer among women, are unclear. Here, we found that decreases in N6AMT1 correlated with the extent of 6mA in clinical BC tissues and predicted a worse survival of BC patients. Functionally, knockdown of N6AMT1 markedly reduced 6mA in DNA and promoted colony formation and migration of BC cells, whereas overexpression of N6AMT1 had the opposite effect. Moreover, silencing of N6AMT1 reduced 6mA modification and enhanced the growth of BC cells in vitro and tumors in vivo. 6mA immunoprecipitation sequencing (6mA-IP-seq), RNA-seq, 6mA-IP-PCR, and bioinformatics analysis indicated that N6AMT1 was a functional methyltransferase for genomic 6mA DNA modifications and related to gene transcriptional activity. Critical negative regulators of the cell cycle, such as RB1, P21, REST, and TP53 were identified as targets of N6AMT1 in BC. These results suggest N6AMT1 enhances DNA 6mA levels to repress tumor progression via transcriptional regulation of cell cycle inhibitors.

DNA N6-methyladenine involvement and regulation of hepatocellular carcinoma development

DNA N6-methyladenine (6 mA) is a new type of DNA methylation identified in various eukaryotic cells. However, its alteration and genomic distribution features in hepatocellular carcinoma (HCC) remain elusive. In this study, we found that N6AMT1 overexpression increased HCC cell viability, suppressed apoptosis, and enhanced migration and invasion, whereas ALKBH1 overexpression induced the opposite effects. Further, 23,779 gain-of-6 mA regions and 11,240 loss-of-6 mA regions were differentially identified in HCC tissues. The differential gain and loss of 6 mA regions were considerably enriched in intergenic regions. Moreover, 7% of the differential 6 mA modifications were associated with tumors, with 60 associated with oncogenes and 57 with tumor suppressor genes (TSGs), and 17 were common to oncogenes and TSGs. The candidate genes affected by 6 mA were filtered by gene ontology (GO) and RNA-seq. Using quantitative polymerase chain reaction (qPCR), BCL2 and PARTICL were found to be correlated with DNA 6 mA in certain HCC processes.

Epigenetic Modulators as Treatment Alternative to Diverse Types of Cancer

DNA is packaged in rolls in an octamer of histones forming a complex of DNA and proteins called chromatin. Chromatin as a structural matrix of a chromosome and its modifications are nowadays considered relevant aspects for regulating gene expression, which has become of high interest in understanding genetic mechanisms regulating various diseases, including cancer. In various types of cancer, the main modifications are found to be DNA methylation in the CpG dinucleotide as a silencing mechanism in transcription, post-translational histone modifications such as acetylation, methylation and others that affect the chromatin structure, the ATP-dependent chromatin remodeling and miRNA-mediated gene silencing. In this review we analyze the main alterations in gene expression, the epigenetic modification patterns that cancer cells present, as well as the main modulators and inhibitors of each epigenetic mechanism and the molecular evolution of the most representative inhibitors, which have opened a promising future in the study of HAT, HDAC, non-glycoside DNMT inhibitors and domain inhibitors.

Using k-mer embeddings learned from a Skip-gram based neural network for building a cross-species DNA N6-methyladenine site prediction model

This study used k-mer embeddings as effective feature to identify DNA N6-Methyladenine sites in plant genomes and obtained improved performance without substantial effort in feature extraction, combination and selection. Identification of DNA N6-methyladenine sites has been a very active topic of computational biology due to the unavailability of suitable methods to identify them accurately, especially in plants. Substantial results were obtained with a great effort put in extracting, heuristic searching, or fusing a diverse types of features, not to mention a feature selection step. In this study, we regarded DNA sequences as textual information and employed natural language processing techniques to decipher hidden biological meanings from those sequences. In other words, we considered DNA, the human life book, as a book corpus for training DNA language models. K-mer embeddings then were generated from these language models to be used in machine learning prediction models. Skip-gram neural networks were the base of the language models and ensemble tree-based algorithms were the machine learning algorithms for prediction models. We trained the prediction model on Rosaceae genome dataset and performed a comprehensive test on 3 plant genome datasets. Our proposed method shows promising performance with AUC performance approaching an ideal value on Rosaceae dataset (0.99), a high score on Rice dataset (0.95) and improved performance on Rice dataset while enjoying an elegant, yet efficient feature extraction process.

DNA methylation-calling tools for Oxford Nanopore sequencing: a survey and human epigenome-wide evaluation

BACKGROUND

Nanopore long-read sequencing technology greatly expands the capacity of long-range, single-molecule DNA-modification detection. A growing number of analytical tools have been developed to detect DNA methylation from nanopore sequencing reads. Here, we assess the performance of different methylation-calling tools to provide a systematic evaluation to guide researchers performing human epigenome-wide studies.

RESULTS

We compare seven analytic tools for detecting DNA methylation from nanopore long-read sequencing data generated from human natural DNA at a whole-genome scale. We evaluate the per-read and per-site performance of CpG methylation prediction across different genomic contexts, CpG site coverage, and computational resources consumed by each tool. The seven tools exhibit different performances across the evaluation criteria. We show that the methylation prediction at regions with discordant DNA methylation patterns, intergenic regions, low CG density regions, and repetitive regions show room for improvement across all tools. Furthermore, we demonstrate that 5hmC levels at least partly contribute to the discrepancy between bisulfite and nanopore sequencing. Lastly, we provide an online DNA methylation database ( https://nanome.jax.org ) to display the DNA methylation levels detected by nanopore sequencing and bisulfite sequencing data across different genomic contexts.

CONCLUSIONS

Our study is the first systematic benchmark of computational methods for detection of mammalian whole-genome DNA modifications in nanopore sequencing. We provide a broad foundation for cross-platform standardization and an evaluation of analytical tools designed for genome-scale modified base detection using nanopore sequencing.

METTL3 promotes the initiation and metastasis of ovarian cancer by inhibiting CCNG2 expression via promoting the maturation of pri-microRNA-1246

Ovarian cancer is a common gynecological malignant tumor with a high mortality rate and poor prognosis. There is inadequate knowledge of the molecular mechanisms underlying ovarian cancer. We examined the expression of methyltransferase-like 3 (METTL3) in tumor specimens using RT-qPCR, immunohistochemistry, and Western blot analysis, and tested the methylation of METTL3 by MSP. Levels of METTL3, miR-1246, pri-miR-1246 and CCNG2 were then analyzed and their effects on cell biological processes were also investigated, using in vivo assay to validate the in vitro findings. METTL3 showed hypomethylation and high expression in ovarian cancer tissues and cells. Hypomethylation of METTL3 was pronounced in ovarian cancer samples, which was negatively associated with patient survival. Decreased METTL3 inhibited the proliferation and migration of ovarian cancer cells and promoted apoptosis, while METTL3 overexpression exerted opposite effects. Mechanistically, METTL3 aggravated ovarian cancer by targeting miR-1246, while miR-1246 targeted and inhibited CCNG2 expression. High expression of METTL3 downregulated CCNG2, promoted the metabolism and growth of transplanted tumors in nude mice, and inhibited apoptosis. The current study highlights the promoting role of METTL3 in the development of ovarian cancer, and presents new targets for its treatment.

Quantification and mapping of DNA modifications

Apart from the four canonical nucleobases, DNA molecules carry a number of natural modifications. Substantial evidence shows that DNA modifications can regulate diverse biological processes. Dynamic and reversible modifications of DNA are critical for cell differentiation and development. Dysregulation of DNA modifications is closely related to many human diseases. The research of DNA modifications is a rapidly expanding area and has been significantly stimulated by the innovations of analytical methods. With the recent advances in methods and techniques, a series of new DNA modifications have been discovered in the genomes of prokaryotes and eukaryotes. Deciphering the biological roles of DNA modifications depends on the sensitive detection, accurate quantification, and genome-wide mapping of modifications in genomic DNA. This review provides an overview of the recent advances in analytical methods and techniques for both the quantification and genome-wide mapping of natural DNA modifications. We discuss the principles, advantages, and limitations of these developed methods. It is anticipated that new methods and techniques will resolve the current challenges in this burgeoning research field and expedite the elucidation of the functions of DNA modifications.

ALKBH1 reduces DNA N6-methyladenine to allow for vascular calcification in chronic kidney disease

Vascular calcification is a common complication of chronic kidney disease (CKD), and one of the main risk factors for increased cardiovascular morbidity and mortality in patients with CKD. In this issue of the JCI, Ouyang and Su et al. report that Alkb homolog 1 (ALKBH1), a DNA demethylase, reduced DNA N6-methyladenine (6mA) in vascular smooth muscle cells (VSMCs) and leukocytes, thus leading to aortic arch calcification in the patients with CKD. During the progression of vascular calcification, increased ALKBH1 expression was linked to decreased 6mA levels, findings that the authors noted in both patients with CKD and CKD mouse models. The kidney and vascular disease risk factor soluble urokinase receptor (suPAR) was also elevated in the plasma. Notably, lower 6mA levels induced BMP2-mediated osteogenic reprogramming in the VSMCs. These findings present a function of ALKBH1 in vascular calcification and provide a framework for therapeutic strategies.

Highly sensitive detection of 6mA at single-base resolution based on A-C mismatch

We first demonstrated that 6mA can be selectively recognized based on the selective ligation reaction of DNA ligase toward A-C mismatch and 6mA-C mismatch. This method, when further combined with amplification using RCA, achieved highly sensitive identification of 6mA in dsDNA at single-base resolution.

End-labeling-based electrochemical strategy for detection of adenine methylation in nucleic acid by differential pulse voltammetry

A promising electrochemical strategy for assay of N6-methyladenosine (m6A)/N6-methyladenine (6mA) in RNA/DNA is proposed. The key of this strategy is the end-labeling of nucleic acid, which makes it possible to detect methylation level in unknown sequence. Firstly, the end of m6A-RNA or 6mA-DNA was labeled with sulfhydryl group through T4 polynucleotide kinase (T4 PNK) and then directly assembled on a gold nanoparticle-modified glassy carbon electrode (AuNPs/GCE). Secondly, methylation sites in RNA/DNA were specifically recognized by anti-m6A-antibody, and then, horseradish peroxidase-labeled goat anti-rabbit IgG (HRP-IgG) was further conjugated on the antibody. Thirdly, HRP-IgG catalyzed the hydroquinone oxidation reaction to generate amplified current signal which correlates with the amount of m6A/6mA in nucleic acid. This method showed a wide linear range from 0.0001 to 10 nM for m6A-RNA, 0.001 to 100 nM for 6mA-dsDNA, and 0.0001 to 10 nM for 6mA-ssDNA. The method was successfully applied to detection of m6A/6mA in RNA/DNA from HeLa cells and E. coli cells and validation of the decrease of m6A-RNA in HeLa cells after treatment with FTO protein.

Demethyltransferase AlkBH1 substrate diversity and relationship to human diseases

AlkBH1 is a member of the AlkB superfamily which are kinds of Fe (II) and α-ketoglutarate (α-KG)-dependent dioxygenases. At present, only demethyltransferases FTO and AlkBH5 have relatively clear substrate studies among these members, the types and mechanisms of substrates catalysis of other members are not clear, especially the demethyltransferase AlkBH1. AlkBH1, as a demethylase, has important functions of reversing DNA methylation and repairing DNA damage. And it has become a promising target for the treatment of many cancers, the regulation of neurological and genetic related diseases. Many scholars have made important discoveries in the diversity of AlkBH1 substrates, but there is no comprehensive summary, which affects the design inhibitor target of AlkBH1. Herein, We are absorbed in the latest progress in the study of AlkBH1 substrate diversity and its relationship with human diseases. Besides, we also discuss future research directions and suggest other studies to reveal the specific catalytic effect of AlkBH1 on cancer substrates.

Epigenetic Regulation in Hydra: Conserved and Divergent Roles

Transitions in gene regulatory processes responsible for the emergence of specialized cell types and spatiotemporal regulation of developmental signaling prior to the divergence of Cnidaria and Bilateria are poorly understood. As a sister group of Bilateria, the phylum Cnidaria can provide significant insights into these processes. Among the cnidarians, hydrae have been studied for >250 years to comprehend the mechanisms underlying their unique immortality and robust regenerative capacity. Studies on Hydra spp. and other pre-bilaterians alike have advanced our understanding of the evolutionary underpinnings governing eumetazoan tissue development, homeostasis, and regeneration. In addition to its regenerative potential, Hydra exhibits continuously active axial patterning due to its peculiar tissue dynamics. These distinctive physiological processes necessitate large scale gene expression changes that are governed by the multitude of epigenetic mechanisms operating in cells. This review highlights the contemporary knowledge of epigenetic regulation in Hydra with contemporary studies from other members of Cnidaria, as well as the interplay between regulatory mechanisms wherever demonstrated. The studies covered in the scope of this review reveal both ancestral and divergent roles played by conserved epigenetic mechanisms with emphasis on transcriptional regulation. Additionally, single-cell transcriptomics data was mined to predict the physiological relevance of putative gene regulatory components, which is in agreement with published findings and yielded insights into the possible functions of the gene regulatory mechanisms that are yet to be deciphered in Hydra, such as DNA methylation. Finally, we delineate potentially rewarding epigenetics research avenues that can further leverage the unique biology of Hydra.

A Mutation-Based Method for Pinpointing a DNA N6 -Methyladenine Methyltransferase Modification Site at Single Base Resolution

DNA N⁶ -methyladenine (6mA) has recently received notable attention due to an increased finding of its functional roles in higher eukaryotes. Here we report an enzyme-assisted chemical labeling method to pinpoint the DNA 6mA methyltransferase (MTase) substrate modification site at single base resolution. A designed allyl-substituted MTase cofactor was applied in the catalytic transfer reaction, and the allyl group was installed to the N⁶ -position of adenine within a specific DNA sequence to form N⁶ -allyladenine (6aA). The iodination of 6aA allyl group induced the formation of 1, N⁶ -cyclized adenine which caused mutations during DNA replication by a polymerase. Thus the modification site could be precisely detected by a mutation signal. We synthesized 6aA deoxynucleoside and deoxynucleotide model compounds and a 6aA-containing DNA probe, and screened nine DNA polymerases to define an optimal system capable of detecting the substrate modification site of a DNA 6mA MTase at single-base resolution.

Single-Nucleotide-Resolution Sequencing of N6-Methyldeoxyadenosine

Use of methylation-specific antibodies with methylated-DNA-immunoprecipitation sequencing allows for the mapping of methylated DNA, such as N⁶-methyldeoxyadenosine (6mA). However, such mapping methods only detect methylated DNA at low resolution. Here, we describe 6mA Cross-linking Exonuclease sequencing (6mACE-seq), which utilizes 6mA-specific antibodies cross-linked to 6mA sites to protect 6mA-DNA fragments from subsequent exonuclease treatment. This allowed 6mACE-seq to map human-genome-wide 6mA at single-nucleotide resolution.