Mapping and elucidating the function of modified bases in DNA

Profiling age and body fluid DNA methylation markers using nanopore adaptive sampling

DNA methylation plays essential roles in regulating physiological processes, from tissue and organ development to gene expression and aging processes and has emerged as a widely used biomarker for the identification of body fluids and age prediction. Currently, methylation markers are targeted independently at specific CpG sites as part of a multiplexed assay rather than through a unified assay. Methylation detection is also dependent on divergent methodologies, ranging from enzyme digestion and affinity enrichment to bisulfite treatment, alongside various technologies for high-throughput profiling, including microarray and sequencing. In this pilot study, we test the simultaneous identification of age-associated and body fluid-specific methylation markers using a single technology, nanopore adaptive sampling. This innovative approach enables the profiling of multiple CpG marker sites across entire gene regions from a single sample without the need for specialized DNA preparation or additional biochemical treatments. Our study demonstrates that adaptive sampling achieves sufficient coverage in regions of interest to accurately determine the methylation status, shows a robust consistency with whole-genome bisulfite sequencing data, and corroborates known CpG markers of age and body fluids. Our work also resulted in the identification of new sites strongly correlated with age, suggesting new possible age methylation markers. This study lays the groundwork for the systematic development of nanopore-based methodologies in both age prediction and body fluid identification, highlighting the feasibility and potential of nanopore adaptive sampling while acknowledging the need for further validation and expansion in future research.

Repair and DNA Polymerase Bypass of Clickable Pyrimidine Nucleotides

Clickable nucleosides, most often 5-ethynyl-2'-deoxyuridine (EtU), are widely used in studies of DNA replication in living cells and in DNA functionalization for bionanotechology applications. Although clickable dNTPs are easily incorporated by DNA polymerases into the growing chain, afterwards they might become targets for DNA repair systems or interfere with faithful nucleotide insertion. Little is known about the possibility and mechanisms of these post-synthetic events. Here, we investigated the repair and (mis)coding properties of EtU and two bulkier clickable pyrimidine nucleosides, 5-(octa-1,7-diyn-1-yl)-U (C8-AlkU) and 5-(octa-1,7-diyn-1-yl)-C (C8-AlkC). In vitro, EtU and C8-AlkU, but not C8-AlkC, were excised by SMUG1 and MBD4, two DNA glycosylases from the base excision repair pathway. However, when placed into a plasmid encoding a fluorescent reporter inactivated by repair in human cells, EtU and C8-AlkU persisted for much longer than uracil or its poorly repairable phosphorothioate-flanked derivative. DNA polymerases from four different structural families preferentially bypassed EtU, C8-AlkU and C8-AlkC in an error-free manner, but a certain degree of misincorporation was also observed, especially evident for DNA polymerase β. Overall, clickable pyrimidine nucleotides could undergo repair and be a source of mutations, but the frequency of such events in the cell is unlikely to be considerable.

Harnessing non-Watson-Crick's base pairing to enhance CRISPR effectors cleavage activities and enable gene editing in mammalian cells

Genomic DNA of the cyanophage S-2L virus is composed of 2-aminoadenine (Z), thymine (T), guanine (G), and cytosine (C), forming the genetic alphabet ZTGC, which violates Watson-Crick base pairing rules. The Z-base has an extra amino group on the two position that allows the formation of a third hydrogen bond with thymine in DNA strands. Here, we explored and expanded applications of this non-Watson-Crick base pairing in protein expression and gene editing. Both ZTGC-DNA (Z-DNA) and ZUGC-RNA (Z-RNA) produced in vitro show detectable compatibility and can be decoded in mammalian cells, including Homo sapiens cells. Z-crRNA can guide CRISPR-effectors SpCas9 and LbCas12a to cleave specific DNA through non-Watson-Crick base pairing and boost cleavage activities compared to A-crRNA. Z-crRNA can also allow for efficient gene and base editing in human cells. Together, our results help pave the way for potential strategies for optimizing DNA or RNA payloads for gene editing therapeutics and give insights to understanding the natural Z-DNA genome.

A non-canonical nucleotide from viral genomes interferes with the oxidative DNA damage repair system

Oxidative damage is a major source of genomic instability in all organisms with the aerobic metabolism. 8-Oxoguanine (8-oxoG), an abundant oxidized purine, is mutagenic and must be controlled by a dedicated DNA repair system (GO system) that prevents G:C→T:A transversions through an easily formed 8-oxoG:A mispair. In some forms, the GO system is present in nearly all cellular organisms. However, recent studies uncovered many instances of viruses possessing non-canonical nucleotides in their genomes. The features of genome damage and maintenance in such cases of alternative genetic chemistry remain barely explored. In particular, 2,6-diaminopurine (Z nucleotide) completely substitutes for A in the genomes of some bacteriophages, which have evolved pathways for dZTP synthesis and specialized polymerases that prefer dZTP over dATP. Here we address the ability of the GO system enzymes to cope with oxidative DNA damage in the presence of Z in DNA. DNA polymerases of two different structural families (Klenow fragment and RB69 polymerase) were able to incorporate dZMP opposite to 8-oxoG in the template, as well as 8-oxodGMP opposite to Z in the template. Fpg, a 8-oxoguanine-DNA glycosylase that discriminates against 8-oxoG:A mispairs, also did not remove 8-oxoG from 8-oxoG:Z mispairs. However, MutY, a DNA glycosylase that excises A from pairs with 8-oxoG, had a significantly lower activity on Z:8-oxoG mispairs. Similar preferences were observed for Fpg and MutY from different bacterial species (Escherichia coli, Staphylococcus aureus and Lactococcus lactis). Overall, the relaxed control of 8-oxoG in the presence of the Z nucleotide may be a source of additional mutagenesis in the genomes of bacteriophages or bacteria that have survived the viral invasion.

DNA Barcodes Using a Dual Nanopore Device

We report a novel method based on the current blockade (CB) characteristics obtained from a dual nanopore device that can determine DNA barcodes with near-perfect accuracy using a Brownian dynamics simulation strategy. The method supersedes our previously reported velocity correction algorithm (S. Seth and A. Bhattacharya, RSC Advances, 11:20781-20787, 2021), taking advantage of the better measurement of the time-of-flight (TOF) protocol offered by the dual nanopore setup. We demonstrate the efficacy of the method by comparing our simulation data from a coarse-grained model of a polymer chain consisting of 2048 excluded volume beads of diameter 𝜎 = 24 bp using with those obtained from experimental CB data from a 48,500 bp λ-phage DNA, providing a 48500 2400 ≅ 24 base pair resolution in simulation. The simulation time scale is compared to the experimental time scale by matching the simulated time-of-flight (TOF) velocity distributions with those obtained experimentally (Rand et al., ACS Nano, 16:5258-5273, 2022). We then use the evolving coordinates of the dsDNA and the molecular features to reconstruct the current blockade characteristics on the fly using a volumetric model based on the effective van der Waal radii of the species inside and in the immediate vicinity of the pore. Our BD simulation mimics the control-zoom-in-logic to understand the origin of the TOF distributions due to the relaxation of the out-of-equilibrium conformations followed by a reversal of the electric fields. The simulation algorithm is quite general and can be applied to differentiate DNA barcodes from different species.

Epitranscriptomics as a New Layer of Regulation of Gene Expression in Skeletal Muscle: Known Functions and Future Perspectives

Epitranscriptomics refers to post-transcriptional regulation of gene expression via RNA modifications and editing that affect RNA functions. Many kinds of modifications of mRNA have been described, among which are N6-methyladenosine (m6A), N1-methyladenosine (m1A), 7-methylguanosine (m7G), pseudouridine (Ψ), and 5-methylcytidine (m5C). They alter mRNA structure and consequently stability, localization and translation efficiency. Perturbation of the epitranscriptome is associated with human diseases, thus opening the opportunity for potential manipulations as a therapeutic approach. In this review, we aim to provide an overview of the functional roles of epitranscriptomic marks in the skeletal muscle system, in particular in embryonic myogenesis, muscle cell differentiation and muscle homeostasis processes. Further, we explored high-throughput epitranscriptome sequencing data to identify RNA chemical modifications in muscle-specific genes and we discuss the possible functional role and the potential therapeutic applications.

DARESOME enables concurrent profiling of multiple DNA modifications with restriction enzymes in single cells and cell-free DNA

5-Methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) are the most abundant DNA modifications that have important roles in gene regulation. Detailed studies of these different epigenetic marks aimed at understanding their combined effects and dynamic interconversion are, however, hampered by the inability of current methods to simultaneously measure both modifications, particularly in samples with limited quantities. We present DNA analysis by restriction enzyme for simultaneous detection of multiple epigenomic states (DARESOME), an assay based on modification-sensitive restriction digest and sequential tag ligation that can concurrently perform quantitative profiling of unmodified cytosine, 5mC, and 5hmC in CCGG sites genome-wide. DARESOME reveals the opposing roles of 5mC and 5hmC in gene expression regulation as well as their interconversion during aging in mouse brain. Implementation of DARESOME in single cells demonstrates pronounced 5hmC strand bias that reflects the semiconservative replication of DNA. Last, we showed that DARESOME enables integrative genomic, 5mC, and 5hmC profiling of cell-free DNA that uncovered multiomics cancer signatures in liquid biopsy.

Exploring the crop epigenome: a comparison of DNA methylation profiling techniques

Epigenetic modifications play a vital role in the preservation of genome integrity and in the regulation of gene expression. DNA methylation, one of the key mechanisms of epigenetic control, impacts growth, development, stress response and adaptability of all organisms, including plants. The detection of DNA methylation marks is crucial for understanding the mechanisms underlying these processes and for developing strategies to improve productivity and stress resistance of crop plants. There are different methods for detecting plant DNA methylation, such as bisulfite sequencing, methylation-sensitive amplified polymorphism, genome-wide DNA methylation analysis, methylated DNA immunoprecipitation sequencing, reduced representation bisulfite sequencing, MS and immuno-based techniques. These profiling approaches vary in many aspects, including DNA input, resolution, genomic region coverage, and bioinformatics analysis. Selecting an appropriate methylation screening approach requires an understanding of all these techniques. This review provides an overview of DNA methylation profiling methods in crop plants, along with comparisons of the efficacy of these techniques between model and crop plants. The strengths and limitations of each methodological approach are outlined, and the importance of considering both technical and biological factors are highlighted. Additionally, methods for modulating DNA methylation in model and crop species are presented. Overall, this review will assist scientists in making informed decisions when selecting an appropriate DNA methylation profiling method.

The effects of epigenetic modifications on bone remodeling in age-related osteoporosis

PURPOSE

As the population ages, there is an increased risk of fracture and morbidity diseases associated with aging, such as age-related osteoporosis and other bone diseases linked to aging skeletons.

RESULTS

Several bone-related cells, including multipotent bone mesenchymal stem cells, osteoblasts that form bone tissue, and osteoclasts that break it down, are in symbiotic relationships throughout life. Growing evidence indicates that epigenetic modifications of cells caused by aging contribute to compromised bone remodeling and lead to osteoporosis. A number of epigenetic mechanisms are at play, including DNA/RNA modifications, histone modifications, microRNAs (miRNAs), and long noncoding RNAs (lncRNAs), as well as chromatin remodeling.

CONCLUSION

In this review, we summarized the epigenetic modifications of different bone-related cells during the development and progression of osteoporosis associated with aging. Additionally, we described a compensatory recovery mechanism under epigenetic regulation that may lead to new strategies for regulating bone remodeling in age-related osteoporosis.

Absolute quantification of single-base m6A methylation in the mammalian transcriptome using GLORI

N6-methyladenosine (m6A) is the most abundant RNA modification in mammalian cells and the best-studied epitranscriptomic mark. Despite the development of various tools to map m6A, a transcriptome-wide method that enables absolute quantification of m6A at single-base resolution is lacking. Here we use glyoxal and nitrite-mediated deamination of unmethylated adenosines (GLORI) to develop an absolute m6A quantification method that is conceptually similar to bisulfite-sequencing-based quantification of DNA 5-methylcytosine. We apply GLORI to quantify the m6A methylomes of mouse and human cells and reveal clustered m6A modifications with differential distribution and stoichiometry. In addition, we characterize m6A dynamics under stress and examine the quantitative landscape of m6A modification in gene expression regulation. GLORI is an unbiased, convenient method for the absolute quantification of the m6A methylome.

Factors and Methods for the Detection of Gene Expression Regulation

Gene-expression regulation involves multiple processes and a range of regulatory factors. In this review, we describe the key factors that regulate gene expression, including transcription factors (TFs), chromatin accessibility, histone modifications, DNA methylation, and RNA modifications. In addition, we also describe methods that can be used to detect these regulatory factors.

Modification mapping by nanopore sequencing

Next generation sequencing (NGS) has provided biologists with an unprecedented view into biological processes and their regulation over the past 2 decades, fueling a wave of development of high throughput methods based on short read DNA and RNA sequencing. For nucleic acid modifications, NGS has been coupled with immunoprecipitation, chemical treatment, enzymatic treatment, and/or the use of reverse transcriptase enzymes with fortuitous activities to enrich for and to identify covalent modifications of RNA and DNA. However, the majority of nucleic acid modifications lack commercial monoclonal antibodies, and mapping techniques that rely on chemical or enzymatic treatments to manipulate modification signatures add additional technical complexities to library preparation. Moreover, such approaches tend to be specific to a single class of RNA or DNA modification, and generate only indirect readouts of modification status. Third generation sequencing technologies such as the commercially available "long read" platforms from Pacific Biosciences and Oxford Nanopore Technologies are an attractive alternative for high throughput detection of nucleic acid modifications. While the former can indirectly sense modified nucleotides through changes in the kinetics of reverse transcription reactions, nanopore sequencing can in principle directly detect any nucleic acid modification that produces a signal distortion as the nucleic acid passes through a nanopore sensor embedded within a charged membrane. To date, more than a dozen endogenous DNA and RNA modifications have been interrogated by nanopore sequencing, as well as a number of synthetic nucleic acid modifications used in metabolic labeling, structure probing, and other emerging applications. This review is intended to introduce the reader to nanopore sequencing and key principles underlying its use in direct detection of nucleic acid modifications in unamplified DNA or RNA samples, and outline current approaches for detecting and quantifying nucleic acid modifications by nanopore sequencing. As this technology matures, we anticipate advances in both sequencing chemistry and analysis methods will lead to rapid improvements in the identification and quantification of these epigenetic marks.

Whole-genome long-read TAPS deciphers DNA methylation patterns at base resolution using PacBio SMRT sequencing technology

Long-read sequencing provides valuable information on difficult-to-map genomic regions, which can complement short-read sequencing to improve genome assembly, yet limited methods are available to accurately detect DNA methylation over long distances at a whole-genome scale. By combining our recently developed TET-assisted pyridine borane sequencing (TAPS) method, which enables direct detection of 5-methylcytosine and 5-hydroxymethylcytosine, with PacBio single-molecule real-time sequencing, we present here whole-genome long-read TAPS (wglrTAPS). To evaluate the performance of wglrTAPS, we applied it to mouse embryonic stem cells as a proof of concept, and an N50 read length of 3.5 kb is achieved. By sequencing wglrTAPS to 8.2× depth, we discovered a significant proportion of CpG sites that were not covered in previous 27.5× short-read TAPS. Our results demonstrate that wglrTAPS facilitates methylation profiling on problematic genomic regions with repetitive elements or structural variations, and also in an allelic manner, all of which are extremely difficult for short-read sequencing methods to resolve. This method therefore enhances applications of third-generation sequencing technologies for DNA epigenetics.

Exploring RNA modifications, editing, and splicing changes in hyperuricemia and gout

Hyperuricemia and gout are two of the most common metabolic disorders worldwide; their incidence is increasing with changes in lifestyle, and they are correlated with many diseases, including renal and cardiovascular diseases. The majority of studies on hyperuricemia and gout have focused on the discovery of the associated genes and their functions and on the roles of monocytes and neutrophils in the development of gout. Virtually no studies investigating the epigenomics of gout disease or exploring the clinical significance of such research have been conducted. In this study, we observed that the expression of enzymes involved in RNA modifications or RNA editing was affected in uric acid (UA)- or monosodium urate (MSU)-treated cell lines. RNA alternative splicing and splicing factors were also affected by UA or MSU treatment. We used transcriptome sequencing to analyze genome-wide RNA splicing and RNA editing and found significant changes in RNA splicing and RNA editing in MSU- or UA-treated THP-1 and HEK293 cells. We further found significant changes of RNA modifications, editing, and splicing in patients with gout. The data indicate that RNA modifications, editing, and splicing play roles in gout. The findings of this study may help to understand the mechanism of RNA splicing and modifications in gout, facilitating the development of new diagnostic and therapeutic strategies.

Lighting Up Nucleic Acid Modifications in Single Cells with DNA-Encoded Amplification

Nucleic acids are naturally decorated with various chemical modifications at nucleobases. Most nucleic acid modifications (NAMs) do not alter Watson-Crick base pairing but can regulate gene expression known as "epigenetics". Their abundances present a very wide range, approximately 10^-2 to 10^-6 of total bases. Different NAMs may coexist in spatial proximity (e.g., <20 nm) in the crowded intracellular environment. Considering the highly dynamic chromatin accessibility (physical access to DNA), the NAMs in inaccessible DNA probably plays different roles. These multilayered features of NAMs vary from cell to cell. Our understanding of the function and mechanism of NAMs in biological processes and disease states has largely been driven by the expanding array of sequencing-based methodologies. However, an underexplored aspect is the measurement of the subcellular distribution, spatial proximity, and inaccessibility of NAMs in single cells. In recent years, we have developed new approaches that light up single-cell NAMs with single-site sensitivity. These methods are mainly based on the integration of chemical or chemoenzymatic tools, DNA amplification and nanotechnology, and/or microfluidics. An overview of these methods together with conventional methods such as immunofluorescence (IF) and fluorescence in situ hybridization (FISH) is provided in this Account.Our laboratory has proposed DNA-encoded amplification (DEA) as the main strategy for developing a set of single-cell NAM imaging methods. In brief, DEA transforms the different features of NAMs into unique DNA primers for rolling circle amplification (RCA) followed by FISH imaging. The first method is base-encoded amplifying FISH (BEA-FISH), in which we convert individual NAMs into RCA primers via chemoselective labeling and click bioconjugation. It enables the in situ visualization of low-abundance NAMs (e.g., 5hmU), which is impracticable by conventional methods. We subsequently developed pairwise proximity-differentiated amplifying FISH (PPDA-FISH), which integrates BEA-FISH with DNA nanotechnology. PPDA-FISH utilizes proximity ligation and toehold strand displacement to label the adjacent site of two different NAMs (one-to-one proximity) and their respective residual sites with three unique RCA probes. It achieves simultaneous counting of the above-mentioned three types of modified sites in the same cells. The third method is cellular macromolecule-tethered DNA walking indexing (Cell-TALKING) to probe more than two NAMs within the same nanoenvironments. Cell-TALKING uses dynamic DNA proximity cleavage to continuously activate different preblocked RCA primers (for each NAM) near one walking probe (for one target molecule). We have explored three NAMs around one histone (one-to-many proximity) in different cancer cell lines and clinical specimens. Then, we describe a single-cell hydrogel encoding amplification (scHEA) method by integrating droplet microfluidics with BEA-FISH. This method generates hydrogel beads that encapsulate single cells and their genomic DNA after cell lysis. It realizes the analysis of global (accessible and inaccessible) DNA from the same cells. We find that the global levels of both 5hmC and 5hmU in single cells can distinguish different breast cancer cells. Finally, the current limitations of these strategies and the future development directions are also discussed. We hope that this Account can spark new ideas and invite new efforts from different disciplines for single-cell NAM analysis.

Determination of 5-formyluracil via oxime-based nucleotide-metal coordination

In this article, a small chemical molecule was synthesized, and its ability to regulate activities of DNA polymerase was tested. In addition, we also used isothermal amplification technology to detect the content of 5-formyluracil sites in irradiated genomic DNA, which confirmed its capability for the detection of 5-formyluracil content in general samples. This study presents the first example of the determination of 5fU based on coordination chemistry.

Quantitative detection of CpG methylation level on G-quadruplex and i-motif-forming DNA by recombinase polymerase amplification

Detection of CpG methylation levels holds immense potential for application in medical diagnosis of various diseases. In this study, we report the development of a recombinase polymerase amplification (RPA)-based CpG methylation level sensing system on G-quadruplex (G4) and intercalated motif (i-motif)-forming regions, which are stabilized by CpG methylation. This detection system is based on the principle that DNA polymerase is stalled at the methylated G4 and i-motif-forming region, which results in a decrease in the initial elongation efficiency of RPA. This reduction in turn affects the onset of amplification depending on the extent of CpG methylation; therefore, the methylation level is quantified by RPA. We demonstrate that the onset of amplification was delayed by CpG methylation when PCR products containing the vascular endothelial growth factor (VEGF) G4 and i-motif-forming region were used as the template. Furthermore, onset of amplification was delayed with the increase in CpG methylation of the VEGF region on genomic DNA. These results demonstrate that the sensing system is capable of directly detecting the methylation level at a constant temperature (39 °C) within 30 min without performing bisulfite conversion or affinity capture of methylated DNA.

Discriminating protein tags on a dsDNA construct using a Dual Nanopore Device

We report Brownian dynamics simulation results with the specific goal to identify key parameters controlling the experimentally measurable characteristics of protein tags on a dsDNA construct translocating through a double nanopore setup. First, we validate the simulation scheme in silico by reproducing and explaining the physical origin of the asymmetric experimental dwell time distributions of the oligonucleotide flap markers on a 48 kbp long dsDNA at the left and the right pore. We study the effect of the electric field inside and beyond the pores, critical to discriminate the protein tags based on their effective charges and masses revealed through a generic power-law dependence of the average dwell time at each pore. The simulation protocols monitor piecewise dynamics at a sub-nanometer length scale and explain the disparate velocity using the concepts of nonequilibrium tension propagation theory. We further justify the model and the chosen simulation parameters by calculating the Péclet number which is in close agreement with the experiment. We demonstrate that our carefully chosen simulation strategies can serve as a powerful tool to discriminate different types of neutral and charged tags of different origins on a dsDNA construct in terms of their physical characteristics and can provide insights to increase both the efficiency and accuracy of an experimental dual-nanopore setup.

Concerted modification of nucleotides at functional centers of the ribosome revealed by single-molecule RNA modification profiling

Nucleotides in RNA and DNA are chemically modified by numerous enzymes that alter their function. Eukaryotic ribosomal RNA (rRNA) is modified at more than 100 locations, particularly at highly conserved and functionally important nucleotides. During ribosome biogenesis, modifications are added at various stages of assembly. The existence of differently modified classes of ribosomes in normal cells is unknown because no method exists to simultaneously evaluate the modification status at all sites within a single rRNA molecule. Using a combination of yeast genetics and nanopore direct RNA sequencing, we developed a reliable method to track the modification status of single rRNA molecules at 37 sites in 18 S rRNA and 73 sites in 25 S rRNA. We use our method to characterize patterns of modification heterogeneity and identify concerted modification of nucleotides found near functional centers of the ribosome. Distinct, undermodified subpopulations of rRNAs accumulate upon loss of Dbp3 or Prp43 RNA helicases, suggesting overlapping roles in ribosome biogenesis. Modification profiles are surprisingly resistant to change in response to many genetic and acute environmental conditions that affect translation, ribosome biogenesis, and pre-mRNA splicing. The ability to capture single-molecule RNA modification profiles provides new insights into the roles of nucleotide modifications in RNA function.

The Dynamic Regulation of G-Quadruplex DNA Structures by Cytosine Methylation

It is well known that certain non B-DNA structures, including G-quadruplexes, are key elements that can regulate gene expression. Here, we explore the theory that DNA modifications, such as methylation of cytosine, could act as a dynamic switch by promoting or alleviating the structural formation of G-quadruplex structures in DNA or RNA. The interaction between epigenetic DNA modifications, G4 formation, and the 3D architecture of the genome is a complex and developing area of research. Although there is growing evidence for such interactions, a great deal still remains to be discovered. In vivo, the potential effect that cytosine methylation may have on the formation of DNA structures has remained largely unresearched, despite this being a potential mechanism through which epigenetic factors could regulate gene activity. Such interactions could represent novel mechanisms for important biological functions, including altering nucleosome positioning or regulation of gene expression. Furthermore, promotion of strand-specific G-quadruplex formation in differentially methylated genes could have a dynamic role in directing X-inactivation or the control of imprinting, and would be a worthwhile focus for future research.

The pH-Dependence of the Hydration of 5-Formylcytosine - an Experimental and Theoretical Study

5-Formylcytosine is an important nucleobase in epigenetic regulation, whose hydrate form has been implicated in the formation of 5-carboxycytosine as well as oligonucleotide binding events. The hydrate content of 5-formylcytosine and its uracil derivative has now been quantified using a combination of NMR and mass spectroscopic measurements as well as theoretical studies. Small amounts of hydrate can be identified for the protonated form of 5-formylcytosine and for neutral 5-formyluracil. For neutral 5-formylcytosine, however, direct detection of the hydrate was not possible due to its very low abundance. This is in full agreement with theoretical estimates.

N4-acetyldeoxycytosine DNA modification marks euchromatin regions in Arabidopsis thaliana

BACKGROUND

Direct analogs of chemically modified bases that carry important epigenetic information, such as 5-methylcytosine (m5C)/5-methyldeoxycytosine (5mC), 5-hydroxymethylcytosine (hm5C)/5-hydroxymethyldeoxycytosine (5hmC), and N6-methyladenosine (m6A)/N6-methyldeoxyadenosine (6mA), are detected in both RNA and DNA, respectively. The modified base N4-acetylcytosine (ac4C) is well studied in RNAs, but its presence and epigenetic roles in cellular DNA have not been explored.

RESULTS

Here, we demonstrate the existence of N4-acetyldeoxycytosine (4acC) in genomic DNA of Arabidopsis with multiple detection methods. Genome-wide profiling of 4acC modification reveals that 4acC peaks are mostly distributed in euchromatin regions and present in nearly half of the expressed protein-coding genes in Arabidopsis. 4acC is mainly located around transcription start sites and positively correlates with gene expression levels. Imbalance of 5mC does not directly affect 4acC modification. We also characterize the associations of 4acC with 5mC and histone modifications that cooperatively regulate gene expression. Moreover, 4acC is also detected in genomic DNA of rice, maize, mouse, and human by mass spectrometry.

CONCLUSIONS

Our findings reveal 4acC as a hitherto unknown DNA modification in higher eukaryotes. We identify potential interactions of this mark with other epigenetic marks in gene expression regulation.

Genomic enhancers in cardiac development and disease

The Human Genome Project marked a major milestone in the scientific community as it unravelled the ~3 billion bases that are central to crucial aspects of human life. Despite this achievement, it only scratched the surface of understanding how each nucleotide matters, both individually and as part of a larger unit. Beyond the coding genome, which comprises only ~2% of the whole genome, scientists have realized that large portions of the genome, not known to code for any protein, were crucial for regulating the coding genes. These large portions of the genome comprise the 'non-coding genome'. The history of gene regulation mediated by proteins that bind to the regulatory non-coding genome dates back many decades to the 1960s. However, the original definition of 'enhancers' was first used in the early 1980s. In this Review, we summarize benchmark studies that have mapped the role of cardiac enhancers in disease and development. We highlight instances in which enhancer-localized genetic variants explain the missing link to cardiac pathogenesis. Finally, we inspire readers to consider the next phase of exploring enhancer-based gene therapy for cardiovascular disease.

Homologues of epigenetic pyrimidines: 5-alkyl-, 5-hydroxyalkyl and 5-acyluracil and -cytosine nucleotides: synthesis, enzymatic incorporation into DNA and effect on transcription with bacterial RNA polymerase

Homologues of natural epigenetic pyrimidine nucleosides and nucleotides were designed and synthesized. They included 5-ethyl-, 5-propyl-, 5-(1-hydroxyethyl)-, 5-(1-hydroxypropyl)- and 5-acetyl- and 5-propionylcytosine and -uracil 2′-deoxyribonucleosides and their corresponding 5′-O-triphosphates (dN^XTPs). The epimers of 5-(1-hydroxyethyl)- and 5-(1-hydroxypropyl)pyrimidine nucleosides were separated and their absolute configuration was determined by a combination of X-ray and NMR analysis. The modified dN^XTPs were used as substrates for PCR synthesis of modified DNA templates used for the study of transcription with bacterial RNA polymerase. Fundamental differences in transcription efficiency were observed, depending on the various modifications. The most notable effects included pronounced stimulation of transcription from 5-ethyluracil-bearing templates (200% transcription yield compared to natural thymine) and an enhancing effect of 5-acetylcytosine versus inhibiting effect of 5-acetyluracil. In summary, these results reveal that RNA polymerase copes with dramatically altered DNA structure and suggest that these nucleobases could potentially play roles as artificial epigenetic DNA nucleobases.

Nucleotides derived from homologues of epigenetic pyrimidine bases were prepared and used for polymerase synthesis of modified DNA templates. Interesting effects of the substituents on PCR and transcription have been observed.

Spiers Memorial Lecture. Next generation nanoelectrochemistry: the fundamental advances needed for applications

Nanoelectrochemistry, where electrochemical processes are controlled and investigated with nanoscale resolution, is gaining more and more attention because of the many potential applications in energy and sensing and the fact that there is much to learn about fundamental electrochemical processes when we explore them at the nanoscale. The development of instrumental methods that can explore the heterogeneity of electrochemistry occurring across an electrode surface, monitoring single molecules or many single nanoparticles on a surface simultaneously, have been pivotal in giving us new insights into nanoscale electrochemistry. Equally important has been the ability to synthesise or fabricate nanoscale entities with a high degree of control that allows us to develop nanoscale devices. Central to the latter has been the incredible advances in nanomaterial synthesis where electrode materials with atomic control over electrochemically active sites can be achieved. After introducing nanoelectrochemistry, this paper focuses on recent developments in two major application areas of nanoelectrochemistry; electrocatalysis and using single entities in sensing. Discussion of the developments in these two application fields highlights some of the advances in the fundamental understanding of nanoelectrochemical systems really driving these applications forward. Looking into our nanocrystal ball, this paper then highlights: the need to understand the impact of nanoconfinement on electrochemical processes, the need to measure many single entities, the need to develop more sophisticated ways of treating the potentially large data sets from measuring such many single entities, the need for more new methods for characterising nanoelectrochemical systems as they operate and the need for material synthesis to become more reproducible as well as possess more nanoscale control.

Epigenome and Epitranscriptome: Potential Resources for Crop Improvement

Crop breeding faces the challenge of increasing food demand, especially under climatic changes. Conventional breeding has relied on genetic diversity by combining alleles to obtain desired traits. In recent years, research on epigenetics and epitranscriptomics has shown that epigenetic and epitranscriptomic diversity provides additional sources for crop breeding and harnessing epigenetic and epitranscriptomic regulation through biotechnologies has great potential for crop improvement. Here, we review epigenome and epitranscriptome variations during plant development and in response to environmental stress as well as the available sources for epiallele formation. We also discuss the possible strategies for applying epialleles and epitranscriptome engineering in crop breeding.

DNA methylation detection technology and plasma-based methylation biomarkers in screening of gastrointestinal carcinoma

DNA methylation is of paramount importance for the evolution of human cancers. Its high sensitivity and specificity make it a potential biomarker for early cancer screening in the context of an increasing global burden of gastrointestinal (GI) carcinoma. More DNA methylation biomarkers are emerging with the development of liquid biopsy and sensitive DNA methylation detection technology. This review provides an overview of DNA methylation, focusing on the presentation and comparison of 5-methylcytosine detection technologies, and introduces the promising plasma-based cell-free DNA (cfDNA) methylation biomarkers published in recent years for early screening of GI carcinoma. Finally, we summarize and discuss the future of plasma cfDNA methylation markers detection as a clinical tool for early screening of GI carcinoma.

Endonuclease enrichment TAPS for cost-effective genome-wide base-resolution DNA methylation detection

Whole genome base-resolution methylome sequencing allows for the most comprehensive analysis of DNA methylation, however, the considerable sequencing cost often limits its applications. While reduced representation sequencing can be an affordable alternative, over 80% of CpGs in the genome are not covered. Building on our recently developed TET-assisted pyridine borane sequencing (TAPS) method, we here described endonuclease enrichment TAPS (eeTAPS), which utilizes dihydrouracil (DHU)-cleaving endonuclease digestion of TAPS-converted DNA to enrich methylated CpG sites (mCpGs). eeTAPS can accurately detect 87% of mCpGs in the mouse genome with a sequencing depth equivalent to 4× whole genome sequencing. In comparison, reduced representation TAPS (rrTAPS) detected less than 4% of mCpGs with 2.5× sequencing depth. Our results demonstrate eeTAPS to be a new strategy for cost-effective genome-wide methylation analysis at single-CpG resolution that can fill the gap between whole-genome and reduced representation sequencing.

Systematic benchmarking of tools for CpG methylation detection from nanopore sequencing

DNA methylation plays a fundamental role in the control of gene expression and genome integrity. Although there are multiple tools that enable its detection from Nanopore sequencing, their accuracy remains largely unknown. Here, we present a systematic benchmarking of tools for the detection of CpG methylation from Nanopore sequencing using individual reads, control mixtures of methylated and unmethylated reads, and bisulfite sequencing. We found that tools have a tradeoff between false positives and false negatives and present a high dispersion with respect to the expected methylation frequency values. We described various strategies to improve the accuracy of these tools, including a consensus approach, METEORE ( https://github.com/comprna/METEORE ), based on the combination of the predictions from two or more tools that shows improved accuracy over individual tools. Snakemake pipelines are also provided for reproducibility and to enable the systematic application of our analyses to other datasets.

Subtraction-free and bisulfite-free specific sequencing of 5-methylcytosine and its oxidized derivatives at base resolution

Although various methods have been developed for sequencing cytosine modifications, it is still challenging for specific and quantitative sequencing of individual modification at base-resolution. For example, to obtain both true 5-methylcytosine (5mC) and true 5-hydroxymethylcytosine (5hmC) information, the two major epigenetic modifications, it usually requires subtraction of two methods, which increases noise and requires high sequencing depth. Recently, we developed TET-assisted pyridine borane sequencing (TAPS) for bisulfite-free direct sequencing of 5mC and 5hmC. Here we demonstrate that two sister methods, TAPSβ and chemical-assisted pyridine borane sequencing (CAPS), can be effectively used for subtraction-free and specific whole-genome sequencing of 5mC and 5hmC, respectively. We also demonstrate pyridine borane sequencing (PS) for whole-genome profiling of 5-formylcytosine and 5-carboxylcytosine, the further oxidized derivatives of 5mC and 5hmC. This work completes the set of versatile borane reduction chemistry-based methods as a comprehensive toolkit for direct and quantitative sequencing of all four cytosine epigenetic modifications.

Coarse-grained modelling of DNA plectoneme pinning in the presence of base-pair mismatches

Damaged or mismatched DNA bases result in the formation of physical defects in double-stranded DNA. In vivo, defects in DNA must be rapidly and efficiently repaired to maintain cellular function and integrity. Defects can also alter the mechanical response of DNA to bending and twisting constraints, both of which are important in defining the mechanics of DNA supercoiling. Here, we use coarse-grained molecular dynamics (MD) simulation and supporting statistical-mechanical theory to study the effect of mismatched base pairs on DNA supercoiling. Our simulations show that plectoneme pinning at the mismatch site is deterministic under conditions of relatively high force (>2 pN) and high salt concentration (>0.5 M NaCl). Under physiologically relevant conditions of lower force (0.3 pN) and lower salt concentration (0.2 M NaCl), we find that plectoneme pinning becomes probabilistic and the pinning probability increases with the mismatch size. These findings are in line with experimental observations. The simulation framework, validated with experimental results and supported by the theoretical predictions, provides a way to study the effect of defects on DNA supercoiling and the dynamics of supercoiling in molecular detail.

Photocaged 5-(Hydroxymethyl)pyrimidine Nucleoside Phosphoramidites for Specific Photoactivatable Epigenetic Labeling of DNA

5-Hydroxymethylcytosine and uracil are epigenetic nucleobases, but their biological roles are still unclear. We present the synthesis of 2-nitrobenzyl photocaged 5-hydroxymethyl-2'-deoxycytidine and uridine 3'-O-phosphoramidites and their use in automated solid-phase synthesis of oligonucleotides (ONs) modified at specific positions. The ONs were used as primers for PCR to construct DNA templates modified in the promoter region that allowed switching of transcription through photochemical uncaging.

Mapping the epigenetic modifications of DNA and RNA

Over 17 and 160 types of chemical modifications have been identified in DNA and RNA, respectively. The interest in understanding the various biological functions of DNA and RNA modifications has lead to the cutting-edged fields of epigenomics and epitranscriptomics. Developing chemical and biological tools to detect specific modifications in the genome or transcriptome has greatly facilitated their study. Here, we review the recent technological advances in this rapidly evolving field. We focus on high-throughput detection methods and biological findings for these modifications, and discuss questions to be addressed as well. We also summarize third-generation sequencing methods, which enable long-read and single-molecule sequencing of DNA and RNA modification.

Msuite: A High-Performance and Versatile DNA Methylation Data-Analysis Toolkit

DNA methylation is a pervasive and important epigenetic regulator in mammalian genome. For DNA methylome profiling, emerging bisulfite-free methods have demonstrated desirable superiority over the conventional bisulfite-treatment-based approaches, although current analysis software could not make full use of their advantages. In this work, we present Msuite, an easy-to-use, all-in-one data-analysis toolkit. Msuite implements a unique 4-letter analysis mode specifically optimized for emerging protocols; it also integrates quality controls, methylation call, and data visualizations. Msuite demonstrates substantial performance improvements over current state-of-the-art tools as well as fruitful functionalities, thus holding the potential to serve as an optimal toolkit to facilitate DNA methylome studies. Source codes and testing datasets for Msuite are freely available at https://github.com/hellosunking/Msuite/.

•

Msuite provides a unique 4-letter analysis mode for emerging bisulfite-free protocols

•

Msuite outperforms current tools in terms of higher accuracy and lower resource usage

•

Msuite has integrated quality control and fruitful data-visualization utilities

•

Msuite provides an all-in-one solution for DNA methylation data analysis

DNA methylation is an essential epigenetic modification responsible for many biological regulation pathways. Despite the fact that various high-throughput methods have been developed for base-resolution DNA methylome profiling, DNA methylation data analysis remains a complex and challenging task. Here, we present Msuite, which has integrated quality control, read alignment, methylation call, and fruitful data-visualization functionalities, aiming to offer an all-in-one package for most of the current DNA methylation profiling assays. Msuite also provides dedicated support for emerging bisulfite-free protocols and outperforms the current tools in terms of higher accuracy and lower computational resource requirement. Hence, Msuite could serve as the optimal toolkit for DNA methylation data analysis as well as facilitating the popularization of emerging bisulfite-free protocols.

Retracted Article: Divergent synthesis of 5-substituted pyrimidine 2'-deoxynucleosides and their incorporation into oligodeoxynucleotides for the survey of uracil DNA glycosylases

Recent studies have indicated that 5-methylcytosine (5mC) residues in DNA can be oxidized and potentially deaminated to the corresponding thymine analogs. Some of these oxidative DNA damages have been implicated as new epigenetic markers that could have profound influences on chromatin function as well as disease pathology. In response to oxidative damage, the cells have a complex network of repair systems that recognize, remove and rebuild the lesions. However, how the modified nucleobases are detected and repaired remains elusive, largely due to the limited availability of synthetic oligodeoxynucleotides (ODNs) containing these novel DNA modifications. A concise and divergent synthetic strategy to 5mC derivatives has been developed. These derivatives were further elaborated to the corresponding phosphoramidites to enable the site-specific incorporation of modified nucleobases into ODNs using standard solid-phase DNA synthesis. The synthetic methodology, along with the panel of ODNs, is of great value to investigate the biological functions of epigenetically important nucleobases, and to elucidate the diversity in chemical lesion repair.

One-Pot Derivatization for Wide-Scope Detection of Nucleobases and Deoxyribosides in Natural Medicinal Foods with Liquid Chromatography-Tandem Mass Spectrometry

A new chemical labeling-based LC-MS/MS approach was developed for quantitative profiling of nine canonical bases and deoxynucleosides (dNs) in natural products. Using 2-bromo-1-(4-dimethylamino-phenyl)-ethaone (BrDPE) as the tagging reagent, a previously unexploited N-alkylpyrimidine derivative (Nad) was created for one-pot labeling of widescope nucleobases via a flexible bromophilic substitution under mild conditions. The derivatization notably improved the LC-MS detection sensitivity by 31-107 fold, enabling a fast dilute-and-shoot analysis of highly diluted samples. The optimized and validated method demonstrated satisfactory accuracy (87-107%), precision (RSDs < 7.5%), and recovery (89-105%) for matrix-matched standard addition. The method was applied to simultaneously determine all target analytes and four uncanonical analogues and base-modified species in seven traditional health foods, which differ in contents by up to 600-fold for discrimination among samples. Further, the base-labeled Nads exhibit a unique fragmentation signature that could be used for untargeted screening of nucleobase-containing metabolites by simplified LC-MS/MS workflow to improve quality evaluation of natural medicinal products.

Key aurophilic motif for robust quantum-tunneling-based characterization of a nucleoside analogue marker

A quantum sequencer offers a scalable electrical platform for single-molecule analysis of genomic events. A thymidine (dT) analog exhibiting uniquely high single-molecule conductance is a key element in capturing DNA synthesis dynamics by serving as a decodable marker for enzymatic labeling of nascent strands. However, the current design strategies of dT analogs that focus on their molecular orbital energy levels require bulky chemical modifications to extend the π-conjugation, which hinders polymerase recognition. We report herein a polymerase-compatible dT analog that is highly identifiable in quantum sequencing. An ethynyl group is introduced as a small gold-binding motif to differentiate the nucleobase-gold electronic coupling, which has been an overlooked factor in modifying nucleobase conductance. The resulting C5-ethynyl-2'-deoxyuridine exhibits characteristic signal profiles that allowed its correct identification at a 93% rate while maintaining polymerase compatibility. This study would expand the applicability of quantum sequencing by demonstrating a robust nucleoside marker with high identifiability.

Site-Selective and Rewritable Labeling of DNA through Enzymatic, Reversible, and Click Chemistries

Current methods for bioconjugation rely on the introduction of stable linkers that lack the required versatility to perform sequential functionalizations. However, sequential manipulations are an increasing requirement in chemical biology because they can underpin multiple analyses of the same sample to provide a wider understanding of cell behavior. Here, we present a new method to site-selectively write, remove, and rewrite chemical functionality to a biomolecule, DNA in this case. Our method combines the precision and robustness of methyltransferase-directed labeling with the reversibility of acyl hydrazones and the efficiency of click chemistry. Underpinning the method is a new S-adenosyl-l-methionine derivative to site-selectively label DNA with a bifunctional chemical handle containing an acyl hydrazone-linker and a terminal azide. Functional tags are conjugated via the azide and can be removed (i.e., untagged) when needed at the acyl hydrazone via exchange with hydroxyl amine. The formed hydrazide-labeled DNA is a versatile intermediate that can be either rewritten to reset the original chemical handle or covalently reacted with a permanent tag. This ability to write, tag, untag, and permanently tag DNA is exploited to sequentially introduce two fluorescent dyes on DNA. Finally, we demonstrate the potential of the method by developing a protocol to sort labeled DNA using magnetic beads, with subsequent amplification of the sorted DNA sample for further analysis. The presented method opens new avenues for site-selective bioconjugation and should underpin integrative approaches in chemical biology where sequential functionalizations of the same sample are required.

A Spontaneous Ring-Opening Reaction Leads to a Repair-Resistant Thymine Oxidation Product in Genomic DNA

The alphabet of modified DNA bases goes beyond the conventional four letters, with biological roles being found for many such modifications. Herein, we describe the observation of a modified thymine base that arises from spontaneous N1 -C2 ring opening of the oxidation product 5-formyl uracil, after N3 deprotonation. We first observed this phenomenon in silico through ab initio calculations, followed by in vitro experiments to verify its formation at a mononucleoside level and in a synthetic DNA oligonucleotide context. We show that the new base modification (Trex , thymine ring expunged) can form under physiological conditions, and is resistant to the action of common repair machineries. Furthermore, we found cases of the natural existence of Trex while screening a number of human cell types and mESC (E14), thus suggesting potential biological relevance of this modification.

Recent advances in the detection of base modifications using the Nanopore sequencer

DNA and RNA modifications have important functions, including the regulation of gene expression. Existing methods based on short-read sequencing for the detection of modifications show difficulty in determining the modification patterns of single chromosomes or an entire transcript sequence. Furthermore, the kinds of modifications for which detection methods are available are very limited. The Nanopore sequencer is a single-molecule, long-read sequencer that can directly sequence RNA as well as DNA. Moreover, the Nanopore sequencer detects modifications on long DNA and RNA molecules. In this review, we mainly focus on base modification detection in the DNA and RNA of mammals using the Nanopore sequencer. We summarize current studies of modifications using the Nanopore sequencer, detection tools using statistical tests or machine learning, and applications of this technology, such as analyses of open chromatin, DNA replication, and RNA metabolism.

Single-Cell Analysis Using Droplet Microfluidics

Droplet microfluidics has revolutionized the study of single cells. The ability to compartmentalize cells within picoliter droplets in microfluidic devices has opened up a wide range of strategies to extract information at the genomic, transcriptomic, proteomic, or metabolomic level from large numbers of individual cells. Studying the different molecular landscapes at single-cell resolution has provided the authors with a detailed picture of intracellular heterogeneity and the resulting changes in cellular phenotypes. In addition, these technologies have aided in the discovery of rare cells in tumors or in the immune system, and left the authors with a deeper understanding of the fundamental biological processes that determine cell fate. This review aims to provide a detailed overview of the various droplet microfluidic strategies reported in the literature, taking into account the sometimes subtle differences in workflow or reagents that enable or improve certain protocols. Specifically, approaches to targeted- and whole-genome analysis, as well as whole-transcriptome profiling techniques, are reviewed. In addition, an up-to-date overview of new methods to characterize and quantify single-cell protein levels, and of developments to screen secreted molecules such as antibodies, cytokines, or metabolites at the single-cell level, is provided.

Chemical-Labeling-Assisted Detection of Nucleobase Modifications by Quantum-Tunneling-Based Single-Molecule Sensing

Quantum-tunneling-based DNA sensing is a single-molecule technique that promises direct mapping of nucleobase modifications. However, its applicability is seriously limited because of the small difference in conductivity between modified and unmodified nucleobases. Herein, a chemical labeling strategy is presented that facilitates the detection of modified nucleotides by quantum tunneling. We used 5-Formyl-2'-deoxyuridine as a model compound and demonstrated that chemical labeling dramatically alters its molecular conductance compared with that of canonical nucleotides; thus, facilitating statistical discrimination, which is impeded in the unlabeled state. This work introduces a chemical strategy that overcomes the intrinsic difficulty in quantum-tunneling-based modification analysis-the similarity of the molecular conductance of the nucleobases of interest.

Enzymatic Synthesis of Base-Functionalized Nucleic Acids for Sensing, Cross-linking, and Modulation of Protein-DNA Binding and Transcription

Protein-DNA interactions are important in replication, transcription, repair, as well as epigenetic modifications of DNA, which involve methylation and demethylation of DNA resulting in regulation of gene expression. Understanding of these processes and chemical tools for studying and perhaps even modulating them could be of great relevance and importance not only in chemical biology but also in real diagnostics and treatment of diseases. In the past decade, we have been working on development of synthesis of base-modified 2'-deoxyribo- or ribonucleoside triphosphates (dNTPs or NTPs) and their use in enzymatic synthesis of modified nucleic acids using DNA or RNA polymerases. These synthetic and enzymatic methods are briefly summarized with focus on recent development and outlining of scope, limitations, and further challenges. The main focus of this Account is on applications of base-modified nucleic acids in sensing of protein-DNA interactions, in covalent cross-linking to DNA-binding proteins ,and in modulation of protein-DNA binding and transcription. Several environment-sensitive fluorescent nucleotides were incorporated to DNA probes which responded to protein binding by light-up, changing of color, or lifetime of fluorescence. Using a cyclodextrin-peptide transporter, fluorescent nucleotides can be transported through the cell membrane and incorporated to genomic DNA. Several dNTPs bearing reactive groups (i.e., vinylsulfonamide or chloroacetamide) were used for polymerase synthesis of DNA reactive probes which cross-link to Cys, His, or Lys in peptides or proteins. An attractive challenge is to use DNA modifications and bioorthogonal reactions in the major groove of DNA for modulation and switching of protein-DNA interactions. We have systematically explored the influence of major-groove modifications on recognition and cleavage of DNA by restriction endonucleases and constructed simple chemical switches of DNA cleavage. Systematic study of the influence of major-groove modifications on transcription with bacterial RNA polymerases revealed not only that some modified bases are tolerated, but also that the presence of 5-hydroxymethyluracil or -cytosine can even enhance the transcription (350 or 250% compared to native DNA). Based on these results, we have constructed the first chemical switch of transcription based on photocaging of hydroxymethylpyrimidines in DNA by 2-nitrobenzyl protection (transcription off), photochemical deprotection of the DNA (transcription on), and enzymatic phosphorylation (only for 5-hydroxymethyluracil, transcription off). Although it has been so far demonstrated only in vitro, it is the proof-of-principle first step toward chemical epigenetics.