One-Pot Chemoenzymatic Cascade for Labeling of the Epigenetic Marker 5-Hydroxymethylcytosine

Long-read structural and epigenetic profiling of a kidney tumor-matched sample with nanopore sequencing and optical genome mapping

Carcinogenesis often involves significant alterations in the cancer genome, marked by large structural variants (SVs) and copy number variations (CNVs) that are difficult to capture with short-read sequencing. Traditionally, cytogenetic techniques are applied to detect such aberrations, but they are limited in resolution and do not cover features smaller than several hundred kilobases. Optical genome mapping (OGM) and nanopore sequencing [Oxford Nanopore Technologies (ONT)] bridge this resolution gap and offer enhanced performance for cytogenetic applications. Additionally, both methods can capture epigenetic information as they profile native, individual DNA molecules. We compared the effectiveness of the two methods in characterizing the structural, copy number and epigenetic landscape of a clear cell renal cell carcinoma tumor. Both methods provided comparable results for basic karyotyping and CNVs, but differed in their ability to detect SVs of different sizes and types. ONT outperformed OGM in detecting small SVs, while OGM excelled in detecting larger SVs, including translocations. Differences were also observed among various ONT SV callers. Additionally, both methods provided insights into the tumor's methylome and hydroxymethylome. While ONT was superior in methylation calling, hydroxymethylation reports can be further optimized. Our findings underscore the importance of carefully selecting the most appropriate platform based on specific research questions.

Long-Read Structural and Epigenetic Profiling of a Kidney Tumor-Matched Sample with Nanopore Sequencing and Optical Genome Mapping

Carcinogenesis often involves significant alterations in the cancer genome architecture, marked by large structural and copy number variations (SVs and CNVs) that are difficult to capture with short-read sequencing. Traditionally, cytogenetic techniques are applied to detect such aberrations, but they are limited in resolution and do not cover features smaller than several hundred kilobases. Optical genome mapping and nanopore sequencing are attractive technologies that bridge this resolution gap and offer enhanced performance for cytogenetic applications. These methods profile native, individual DNA molecules, thus capturing epigenetic information. We applied both techniques to characterize a clear cell renal cell carcinoma (ccRCC) tumor's structural and copy number landscape, highlighting the relative strengths of each method in the context of variant size and average read length. Additionally, we assessed their utility for methylome and hydroxymethylome profiling, emphasizing differences in epigenetic analysis applicability.

Chemo-Enzymatic Fluorescence Labeling Of Genomic DNA For Simultaneous Detection Of Global 5-Methylcytosine And 5-Hydroxymethylcytosine

5-Methylcytosine and 5-hydroxymethylcytosine are epigenetic modifications involved in gene regulation and cancer. We present a new, simple, and high-throughput platform for multi-color epigenetic analysis. The novelty of our approach is the ability to multiplex methylation and de-methylation signals in the same assay. We utilize an engineered methyltransferase enzyme that recognizes and labels all unmodified CpG sites with a fluorescent cofactor. In combination with the already established labeling of the de-methylation mark 5-hydroxymethylcytosine via enzymatic glycosylation, we obtained a robust platform for simultaneous epigenetic analysis of these marks. We assessed the global epigenetic levels in multiple samples of colorectal cancer and observed a 3.5-fold reduction in 5hmC levels but no change in DNA methylation levels between sick and healthy individuals. We also measured epigenetic modifications in chronic lymphocytic leukemia and observed a decrease in both modification levels (5-hydroxymethylcytosine: whole blood 30 %; peripheral blood mononuclear cells (PBMCs) 40 %. 5-methylcytosine: whole blood 53 %; PBMCs 48 %). Our findings propose using a simple blood test as a viable method for analysis, simplifying sample handling in diagnostics. Importantly, our results highlight the assay's potential for epigenetic evaluation of clinical samples, benefiting research and patient management.

N4 -allyldeoxycytidine: A New DNA Tag with Chemical Sequencing Power for Pinpointing Labelling Sites, Mapping Epigenetic Mark, and in situ Imaging

DNA tagging with base analogs has found numerous applications. To precisely record the DNA labelling information, it will be highly beneficial to develop chemical sequencing tags that can be encoded into DNA as regular bases and decoded as mutant bases upon a mild, efficient and bioorthognal chemical treatment. Here we reported such a DNA tag, N4-allyldeoxycytidine (a4dC), to label and identify DNA by in vitro assays. The iodination of a4dC led to fast and complete formation of 3, N4-cyclized deoxycytidine, which induced base misincorporation during DNA replication and thus could be located at single base resolution. We explored the applications of a4dC in pinpointing DNA labelling sites at single base resolution, mapping epigenetic mark N4-methyldeoxycytidine, and imaging nucleic acids in situ. In addition, mammalian cellular DNA could be metabolically labelled with a4dC. Together，our study sheds light on the design of next generation DNA tags with chemical sequencing power.

Single-molecule optical genome mapping in nanochannels: multidisciplinarity at the nanoscale

The human genome contains multiple layers of information that extend beyond the genetic sequence. In fact, identical genetics do not necessarily yield identical phenotypes as evident for the case of two different cell types in the human body. The great variation in structure and function displayed by cells with identical genetic background is attributed to additional genomic information content. This includes large-scale genetic aberrations, as well as diverse epigenetic patterns that are crucial for regulating specific cell functions. These genetic and epigenetic patterns operate in concert in order to maintain specific cellular functions in health and disease. Single-molecule optical genome mapping is a high-throughput genome analysis method that is based on imaging long chromosomal fragments stretched in nanochannel arrays. The access to long DNA molecules coupled with fluorescent tagging of various genomic information presents a unique opportunity to study genetic and epigenetic patterns in the genome at a single-molecule level over large genomic distances. Optical mapping entwines synergistically chemical, physical, and computational advancements, to uncover invaluable biological insights, inaccessible by sequencing technologies. Here we describe the method's basic principles of operation, and review the various available mechanisms to fluorescently tag genomic information. We present some of the recent biological and clinical impact enabled by optical mapping and present recent approaches for increasing the method's resolution and accuracy. Finally, we discuss how multiple layers of genomic information may be mapped simultaneously on the same DNA molecule, thus paving the way for characterizing multiple genomic observables on individual DNA molecules.

Covalent labeling of nucleic acids

Labeling of nucleic acids is required for many studies aiming to elucidate their functions and dynamics in vitro and in cells. Out of the numerous labeling concepts that have been devised, covalent labeling provides the most stable linkage, an unrivaled choice of small and highly fluorescent labels and - thanks to recent advances in click chemistry - an incredible versatility. Depending on the approach, site-, sequence- and cell-specificity can be achieved. DNA and RNA labeling are rapidly developing fields that bring together multiple areas of research: on the one hand, synthetic and biophysical chemists develop new fluorescent labels and isomorphic nucleobases as well as faster and more selective bioorthogonal reactions. On the other hand, the number of enzymes that can be harnessed for post-synthetic and site-specific labeling of nucleic acids has increased significantly. Together with protein engineering and genetic manipulation of cells, intracellular and cell-specific labeling has become possible. In this review, we provide a structured overview of covalent labeling approaches for nucleic acids and highlight notable developments, in particular recent examples. The majority of this review will focus on fluorescent labeling; however, the principles can often be readily applied to other labels. We will start with entirely chemical approaches, followed by chemo-enzymatic strategies and ribozymes, and finish with metabolic labeling of nucleic acids. Each section is subdivided into direct (or one-step) and two-step labeling approaches and will start with DNA before treating RNA.

Rapid Quantification of Oxidation and UV Induced DNA Damage by Repair Assisted Damage Detection-(Rapid RADD)

Knowing the amount and type of DNA damage is of great significance for a broad range of clinical and research applications. However, existing methods are either lacking in their ability to distinguish between types of DNA damage or limited in their sensitivity and reproducibility. The method described herein enables rapid and robust quantification of type-specific single-strand DNA damage. The method is based on repair-assisted damage detection (RADD) by which fluorescent nucleotides are incorporated into DNA damage sites using type-specific repair enzymes. Up to 90 DNA samples are then deposited on a multiwell glass slide, and analyzed by a conventional slide scanner for quantification of DNA damage levels. Accurate and sensitive measurements of oxidative or UV-induced DNA damage levels and repair kinetics are presented for both in vitro and in vivo models.

Simultaneous detection of multiple DNA damage types by multi-colour fluorescent labelling

Herein we present an assay allowing concurrent detection of oxidative DNA damage and photoproducts. We apply DNA repair enzymes specific for each lesion type to incorporate spectrally distinct fluorescent nucleotides, enabling simultaneous quantification of the lesions on individual DNA molecules. We follow the repair of both damage types in skin cells exposed to artificial sunlight.

Global modulation in DNA epigenetics during pro-inflammatory macrophage activation

DNA methylation patterns create distinct gene-expression profiles. These patterns are maintained after cell division, thus enabling the differentiation and maintenance of multiple cell types from the same genome sequence. The advantage of this mechanism for transcriptional control is that chemical-encoding allows to rapidly establish new epigenetic patterns 'on-demand' through enzymatic methylation and demethylation of DNA. Here we show that this feature is associated with the fast response of macrophages during their pro-inflammatory activation. By using a combination of mass spectroscopy and single-molecule imaging to quantify global epigenetic changes in the genomes of primary macrophages, we followed three distinct DNA marks (methylated, hydroxymethylated and unmethylated), involved in establishing new DNA methylation patterns during pro-inflammatory activation. The observed epigenetic modulation together with gene-expression data generated for the involved enzymatic machinery may suggest that de-methylation upon LPS-activation starts with oxidation of methylated CpGs, followed by excision-repair of these oxidized bases and their replacement with unmodified cytosine.

5-Hydroxymethylcytosine as a clinical biomarker: Fluorescence-based assay for high-throughput epigenetic quantification in human tissues

Epigenetic transformations may provide early indicators for cancer and other disease. Specifically, the amount of genomic 5-hydroxymethylcytosine (5-hmC) was shown to be globally reduced in a wide range of cancers. The integration of this global biomarker into diagnostic workflows is hampered by the limitations of current 5-hmC quantification methods. Here we present and validate a fluorescence-based platform for high-throughput and cost-effective quantification of global genomic 5-hmC levels. We utilized the assay to characterize cancerous tissues based on their 5-hmC content, and observed a pronounced reduction in 5-hmC level in various cancer types. We present data for glioblastoma, colorectal cancer, multiple myeloma, chronic lymphocytic leukemia and pancreatic cancer, compared to corresponding controls. Potentially, the technique could also be used to follow response to treatment for personalized treatment selection. We present initial proof-of-concept data for treatment of familial adenomatous polyposis.

Long-read single-molecule maps of the functional methylome

We report on the development of a methylation analysis workflow for optical detection of fluorescent methylation profiles along chromosomal DNA molecules. In combination with Bionano Genomics genome mapping technology, these profiles provide a hybrid genetic/epigenetic genome-wide map composed of DNA molecules spanning hundreds of kilobase pairs. The method provides kilobase pair–scale genomic methylation patterns comparable to whole-genome bisulfite sequencing (WGBS) along genes and regulatory elements. These long single-molecule reads allow for methylation variation calling and analysis of large structural aberrations such as pathogenic macrosatellite arrays not accessible to single-cell second-generation sequencing. The method is applied here to study facioscapulohumeral muscular dystrophy (FSHD), simultaneously recording the haplotype, copy number, and methylation status of the disease-associated, highly repetitive locus on Chromosome 4q.

Efficient chemoenzymatic synthesis of UDP-α-6-N3-glucose

A novel chemo-enzymatic synthetic method for UDP-α-6-N₃-glucose was developed by combining the versatility of chemical synthesis and natural enzyme stereo-selectivity of Bifidobacterium longum (BLUSP). This flexible and efficient platform expanded the substrate scope for UDP-sugars on an improved scale, particularly for UDP-sugar substrates containing bioorthogonal functional groups.

Microfluidic DNA combing for parallel single-molecule analysis

DNA combing is a widely used method for stretching and immobilising DNA molecules on a surface. Fluorescent labelling of genomic information enables high-resolution optical analysis of DNA at the single-molecule level. Despite its simplicity, the application of DNA combing in diagnostic workflows is still limited, mainly due to difficulties in analysing multiple small-volume DNA samples in parallel. Here, we report a simple and versatile microfluidic DNA combing technology (μDC), which allows manipulating, stretching and imaging of multiple, microliter scale DNA samples by employing a manifold of parallel microfluidic channels. Using DNA molecules with repetitive units as molecular rulers, we demonstrate that the μDC technology allows uniform stretching of DNA molecules. The stretching ratio remains consistent along individual molecules as well as between different molecules in the various channels, allowing simultaneous quantitative analysis of different samples loaded into parallel channels. Furthermore, we demonstrate the application of μDC to characterise UVB-induced DNA damage levels in human embryonic kidney cells and the spatial correlation between DNA damage sites. Our results point out the potential application of μDC for quantitative and comparative single-molecule studies of genomic features. The extremely simple design of μDC makes it suitable for integration into other microfluidic platforms to facilitate high-throughput DNA analysis in biological research and medical point-of-care applications.

Repurposing enzymatic transferase reactions for targeted labeling and analysis of DNA and RNA

Produced as linear biopolymers from four major types of building blocks, DNA and RNA are further furnished with a range of covalent modifications. Despite the impressive specificity of natural enzymes, the transferred groups are often poor reporters and not amenable to further derivatization. Therefore, strategies based on repurposing some of these enzymatic reactions to accept derivatized versions of the transferrable groups have been exploited. By far the most widely used are S-adenosylmethionine-dependent methyltransferases, which along with several other nucleic acids modifying enzymes offer a broad selection of tagging chemistries and molecular features on DNA and RNA that can be targeted in vitro and in vivo. Engineered enzymatic reactions have been implemented in validated DNA sequencing-based protocols for epigenome analysis. The utility of chemo-enzymatic labeling is further enhanced with recent advances in physical detection of individual reporter groups on DNA using super resolution microscopy and nanopore sensing enabling single-molecule multiplex analysis of genetic and epigenetic marks in minute samples. Altogether, a number of new powerful techniques are currently in use or on the verge of real benchtop applications as research tools or next generation diagnostics.

Irys Extract

Summary

Irys Extract is a software tool for generating genomic information from data collected by the BioNano Genomics Irys platform. The tool allows the user easy access to the raw data in the form of cropped images and genetically aligned intensity profiles. The latter are also made compatible with the BED format for using with popular genomic browsers such as the UCSC Genome Browser.

Availability and implementation

Irys Extract has been developed in Matlab R2015a, it was tested to work with IrysView 2.4.0.15879 and AutoDetect 2.1.4.9159, and it currently runs under Microsoft Windows operating systems (7-10). Irys Extract can be downloaded alongside its manual and a demo dataset at http://www.nanobiophotonix.com and https://sites.google.com/site/raniarielly/.

Supplementary information

Supplementary data are available at Bioinformatics online.

Hypersensitive quantification of global 5-hydroxymethylcytosine by chemoenzymatic tagging

5-hydroxymethylcytosine (5hmC) is an epigenetic DNA modification. Tissue-specific reduction in global 5hmC levels has been associated with various types of cancer. One of the challenges associated with detecting 5hmC levels is its extremely low content, especially in blood. The gold-standard for reliable global 5hmC quantitation is liquid chromatography-tandem mass spectroscopy (LC-MS/MS) operating in a multiple reaction monitoring (MRM) mode. Difficulties associated with 5hmC detection by LC-MS/MS include its low abundance, low ionization efficiency and possible ion suppression from co-eluted compounds. Hence, detecting 5hmC levels in blood samples for diagnosis of leukemia and other blood malignancies presents a unique challenge. To overcome these difficulties we introduce a simple chemoenzymatic method for specifically tagging 5hmC, resulting in an eight-fold increase in detection sensitivity. We demonstrate that we could quantitatively detect 5hmC levels in various human tissues, including blood samples from healthy individuals and leukemia patients, using the most basic quadrupole mass-analyzer instrument and only 200 ng of DNA. The limit of detection (LOD) of our technique is 0.001% 5hmC from 300 ng DNA, sufficient for future mass-spectroscopy based diagnostics of diseases associated with low 5hmC levels such as leukemia.

Chemistry-Driven Epigenetic Investigation of Histone and DNA Modifications

In the regulation processes of gene expression, genomic DNA and nuclear proteins, including histone proteins, cooperate with each other, leading to the distinctive functions of eukaryotic cells such as pluripotency and differentiation. Chemical modification of histone proteins and DNA has been revealed as one of the major driving forces in the complicated epigenetic regulation system. However, understanding of the precise molecular mechanisms is still limited. To address this issue, researchers have proposed both biological and chemical strategies for the preparation and detection of modified proteins and nucleic acids. In this review, we focus on chemical methods around the field of epigenetics. Chemical protein synthesis has enabled the preparation of site-specifically modified histones and their successful application to various in vitro assays, which have emphasized the significance of posttranslational modifications of interest. We also review the modification-specific chemical reactions against synthetic and genomic DNA, which enabled discrimination of several modified bases at single-base resolution.

Epigenetic Optical Mapping of 5-Hydroxymethylcytosine in Nanochannel Arrays

The epigenetic mark 5-hydroxymethylcytosine (5-hmC) is a distinct product of active DNA demethylation that is linked to gene regulation, development, and disease. In particular, 5-hmC levels dramatically decline in many cancers, potentially serving as an epigenetic biomarker. The noise associated with next-generation 5-hmC sequencing hinders reliable analysis of low 5-hmC containing tissues such as blood and malignant tumors. Additionally, genome-wide 5-hmC profiles generated by short-read sequencing are limited in providing long-range epigenetic information relevant to highly variable genomic regions, such as the 3.7 Mbp disease-related Human Leukocyte Antigen (HLA) region. We present a long-read, highly sensitive single-molecule mapping technology that generates hybrid genetic/epigenetic profiles of native chromosomal DNA. The genome-wide distribution of 5-hmC in human peripheral blood cells correlates well with 5-hmC DNA immunoprecipitation (hMeDIP) sequencing. However, the long single-molecule read-length of 100 kbp to 1 Mbp produces 5-hmC profiles across variable genomic regions that failed to show up in the sequencing data. In addition, optical 5-hmC mapping shows a strong correlation between the 5-hmC density in gene bodies and the corresponding level of gene expression. The single-molecule concept provides information on the distribution and coexistence of 5-hmC signals at multiple genomic loci on the same genomic DNA molecule, revealing long-range correlations and cell-to-cell epigenetic variation.

Synthesis of 4-Azido-N-acetylhexosamine Uridine Diphosphate Donors: Clickable Glycosaminoglycans

Unnatural chemically modified nucleotide sugars UDP-4-N3-GlcNAc and UDP-4-N3-GalNAc were chemically synthesized for the first time. These unnatural UDP sugar products were then tested for incorporation into hyaluronan, heparosan, or chondroitin using polysaccharide synthases. UDP-4-N3-GlcNAc served as a chain termination substrate for hyaluronan or heparosan synthases; the resulting 4-N3-GlcNAc-terminated hyaluronan and heparosan were then successfully conjugated with Alexa Fluor 488 DIBO alkyne, demonstrating that this approach is generally applicable for labeling and detection of suitable glycosaminoglycans.

Single-molecule quantification of 5-hydroxymethylcytosine for diagnosis of blood and colon cancers

Background

The DNA modification 5-hydroxymethylcytosine (5hmC) is now referred to as the sixth base of DNA with evidence of tissue-specific patterns and correlation with gene regulation and expression. This epigenetic mark was recently reported as a potential biomarker for multiple types of cancer, but its application in the clinic is limited by the utility of recent 5hmC quantification assays. We use a recently developed, ultra-sensitive, fluorescence-based single-molecule method for global quantification of 5hmC in genomic DNA. The high sensitivity of the method gives access to precise quantification of extremely low 5hmC levels common in many cancers.

Methods

We assessed 5hmC levels in DNA extracted from a set of colon and blood cancer samples and compared 5hmC levels with healthy controls, in a single-molecule approach.

Results

Using our method, we observed a significantly reduced level of 5hmC in blood and colon cancers and could distinguish between colon tumor and colon tissue adjacent to the tumor based on the global levels of this molecular biomarker.

Conclusions

Single-molecule detection of 5hmC allows distinguishing between malignant and healthy tissue in clinically relevant and accessible tissue such as blood and colon. The presented method outperforms current commercially available quantification kits and may potentially be developed into a widely used, 5hmC quantification assay for research and clinical diagnostics. Furthermore, using this method, we confirm that 5hmC is a good molecular biomarker for diagnosing colon and various types of blood cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s13148-017-0368-9) contains supplementary material, which is available to authorized users.

Chemoenzymatic Synthesis of 4-Fluoro-N-Acetylhexosamine Uridine Diphosphate Donors: Chain Terminators in Glycosaminoglycan Synthesis

Unnatural uridine diphosphate (UDP)-sugar donors, UDP-4-deoxy-4-fluoro-N-acetylglucosamine (4FGlcNAc) and UDP-4-deoxy-4-fluoro-N-acetylgalactosamine (4FGalNAc), were prepared using both chemical and chemoenzymatic syntheses relying on N-acetylglucosamine-1-phosphate uridylyltransferase (GlmU). The resulting unnatural UDP-sugar donors were then tested as substrates in glycosaminoglycan synthesis catalyzed by various synthases. UDP-4FGlcNAc was transferred onto an acceptor by Pastuerella multocida heparosan synthase 1 and subsequently served as a chain terminator.

Simple and cost-effective fluorescent labeling of 5-hydroxymethylcytosine

The nucleobase 5-hydroxymethylcytosine (5-hmC), a modified form of cytosine, is an important epigenetic mark related to regulation of gene expression. 5-hmC levels are highly dynamic during early development and are modulated during the progression of neurodegenerative disease and cancer. We describe a spectroscopic method for the global quantification of 5-hmC in genomic DNA. This method relies on the enzymatic glucosylation of 5-hmC, followed by a glucose oxidation step that results in the formation of aldehyde moieties that are covalently linked to a fluorescent reporter by oxime ligation. The fluorescence intensity of the labeled sample is directly proportional to its 5-hmC content. We show that this simple and cost-effective technique is suitable for quantification of 5-hmC content in different mouse tissues.

Simultaneous single-molecule epigenetic imaging of DNA methylation and hydroxymethylation

The modifications 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) are the two major DNA epigenetic modifications in mammalian genomes and play crucial roles in development and pathogenesis. Little is known about the colocalization or potential correlation of these two modifications. Here we present an ultrasensitive single-molecule imaging technology capable of detecting and quantifying 5hmC and 5mC from trace amounts of DNA. We used this approach to perform single-molecule fluorescence resonance energy transfer (smFRET) experiments which measure the proximity between 5mC and 5hmC in the same DNA molecule. Our results reveal high levels of adjacent and opposing methylated and hydroxymethylated CpG sites (5hmC/5mCpGs) in mouse genomic DNA across multiple tissues. This identifies the previously undetectable and unappreciated 5hmC/5mCpGs as one of the major states for 5hmC in the mammalian genome and suggest that they could function in promoting gene expression.

Investigation of various fluorescent protein–DNA binding peptides for effectively visualizing large DNA molecules

Single-molecule DNA visualization with fluorescent protein DNA binding peptides.