Analytical epigenetics: single-molecule optical detection of DNA and histone modifications

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.

Super-resolution imaging of linearized chromatin in tunable nanochannels

Nanofluidic linearization and optical mapping of naked DNA have been reported in the research literature, and implemented in commercial instruments. However, the resolution with which DNA features can be resolved is still inherently limited by both Brownian motion and diffraction-limited optics. Direct analysis of native chromatin is further hampered by difficulty in electrophoretic manipulation, which is routinely used for DNA analysis. This paper describes the development of a three-layer, tunable, nanochannel system that enables non-electrophoretic linearization and immobilization of native chromatin. Furthermore, through careful selection of self-blinking fluorescent dyes and the design of the nanochannel system, we achieve direct stochastic optical reconstruction microscopy (dSTORM) super-resolution imaging of the linearized chromatin. As an initial demonstration, rDNA chromatin extracted from Tetrahymena is analyzed by multi-color imaging of total DNA, newly synthesized DNA, and newly synthesized histone H3. Our analysis reveals a relatively even distribution of newly synthesized H3 across two halves of the rDNA chromatin with palindromic symmetry, supporting dispersive nucleosome segregation. As a proof-of-concept study, our work achieves super-resolution imaging of native chromatin fibers linearized and immobilized in tunable nanochannels. It opens up a new avenue for collecting long-range and high-resolution epigenetic information as well as genetic information.

Dam Assisted Fluorescent Tagging of Chromatin Accessibility (DAFCA) for Optical Genome Mapping in Nanochannel Arrays

Proteins and enzymes in the cell nucleus require physical access to their DNA target sites in order to perform genomic tasks such as gene activation and transcription. Hence, chromatin accessibility is a central regulator of gene expression, and its genomic profile holds essential information on the cell type and state. We utilized the E. coli Dam methyltransferase in combination with a fluorescent cofactor analogue to generate fluorescent tags in accessible DNA regions within the cell nucleus. The accessible portions of the genome are then detected by single-molecule optical genome mapping in nanochannel arrays. This method allowed us to characterize long-range structural variations and their associated chromatin structure. We show the ability to create whole-genome, allele-specific chromatin accessibility maps composed of long DNA molecules extended in silicon nanochannels.

Sensing Base Modifications in Non-Canonically Folded DNA with an Optimized Host:Guest Sensing Array

An arrayed host:guest fluorescence sensor system can discriminate DNA G-quadruplex structures that differ only in the presence of single oxidation or methylation modification in the guanine base. These small modifications make subtle changes to G4 folding that are often not detectable by CD but induce differential fluorescence responses in the array. The sensing is functional in diluted serum and is capable of distinguishing individual modifications in DNA mixtures, providing a powerful method of detecting folding changes caused by DNA damage.

Electrochemical DNA Biosensors Based on the Intrinsic Topological Insulator BiSbTeSe2 for Potential Application in HIV Determination

In this work, we reported a sensitive, label-free electrochemical biosensor based on the intrinsic topological insulator (TI) BiSbTeSe₂ for potential application in the determination of the HIV gene. With strong spin-obit coupling, TIs could have robust surface states with low electronic noise, which might be beneficial for the stable and sensitive electron transport between the electrode and electrolyte interface. Under optimized conditions of the biosensors using BiSbTeSe₂, the differential pulse voltammetry (DPV) peak currents showed a linear relationship with the logarithm of target DNA concentrations ranging from 1.0 × 10^-13 to 1.0 × 10^-7 M, with a detection limit of 1.07 × 10^-15 M. The sensing assay also displayed good selectivity and stability after storage at 4 °C for 7 days. This work provides an effective way to develop biosensors with topological materials, which have a potential application in the clinical determination and monitoring field.

Biophysics is reshaping our perception of the epigenome: from DNA-level to high-throughput studies

Epigenetic research holds great promise to advance our understanding of biomarkers and regulatory processes in health and disease. An increasing number of new approaches, ranging from molecular to biophysical analyses, enable identifying epigenetic changes on the level of a single gene or the whole epigenome. The aim of this review is to highlight how the field is shifting from completely molecular-biology-driven solutions to multidisciplinary strategies including more reliance on biophysical analysis tools. Biophysics not only offers technical advancements in imaging or structure analysis but also helps to explore regulatory interactions. New computational methods are also being developed to meet the demand of growing data volumes and their processing. Therefore, it is important to capture these new directions in epigenetics from a biophysical perspective and discuss current challenges as well as multiple applications of biophysical methods and tools. Specifically, we gradually introduce different biophysical research methods by first considering the DNA-level information and eventually higher-order chromatin structures. Moreover, we aim to highlight that the incorporation of bioinformatics, machine learning, and artificial intelligence into biophysical analysis allows gaining new insights into complex epigenetic processes. The gained understanding has already proven useful in translational and clinical research providing better patient stratification options or new therapeutic insights. Together, this offers a better readiness to transform bench-top experiments into industrial high-throughput applications with a possibility to employ developed methods in clinical practice and diagnostics.

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.

Label as you fold: methyltransferase-assisted functionalization of DNA nanostructures

Non-DNA labels are key components for the construction of functional DNA nanostructures. Here, we present a method to graft covalent labels onto DNA origami nanostructures in an enzymatic one-pot reaction. The DNA methyltransferase M.TaqI labels the DNA nanostructures with azide groups, which serve as universal attachment points via click chemistry. Direct labeling with fluorescent dyes is also demonstrated. The procedure yields structures with high fluorescence intensities and narrow intensity distributions. In combination with UV crosslinking it enables the creation of temperature-stable, intense fluorescent beacons.

Hydrogen bonding and protonation effects in amino acids' anthraquinone derivatives - Spectroscopic and electrochemical studies

Six novel amino acid chromophores were synthesized and their spectroscopic, acid-base, and electrochemical properties are discussed in this work. In studied compounds, selected amino acid residues (l-Aspartic acid, l-Glutamic acid, l-Glutamine, l-Histidine, l-Lysine, l-Arginine) are attached to the 1-(piperazine) 9,10-anthraquinone skeleton via the amide bond between the carboxyl group of amino acid and nitrogen atom of the piperazine ring. All derivatives have been characterized using a variety of spectroscopic techniques (mass spectrometry, 1HNMR, UV-Vis, IR spectroscopy), acid-base (electrochemical and UV-Vis) titrations, and cyclic voltammetry methods. Basing on observed experimental effects, supported by quantum chemical simulations, the structure-properties links were established. They are indicative of the specific interactions within and/or in-between amino acid side groups, which are prone to form both, intra- and intermolecular hydrogen bonds as well as electrostatic interactions with the anthraquinone system.

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.