Cellular macromolecules-tethered DNA walking indexing to explore nanoenvironments of chromatin modifications

Molecule Differentiation Encoding Microscopy to Dissect Dense Biomolecules in Cellular Nanoenvironments below Spatial Resolution

Cellular biomolecules may exhibit dense distribution and organization at the nanoscale to govern vital biological processes. However, it remains a common challenge to digitize the spatially dense biomolecules under the spatial resolution of microscopies. Here, a proof-of-principle method, molecule differentiation encoding microscopy by orthogonal tandem repeat DNA identifiers is reported, to resolve the copy numbers of dense biomolecules in cellular nanoenvironments. The method encodes each copy of the same biomolecules into different types of DNA barcodes based on stochastic multiplexed reactions. It can transform the overlap of the same spectrum into the overlap of different spectra. Furthermore, an algorithm is developed to automatically quantitate overlapping spots and individual spots. Using this method, RNAs in the cytoplasm, DNA epigenetic modifications in the cell nucleus, and glycans and glycoRNAs on the cell surface are dissected, respectively. It is found that all these biomolecules present dense distribution with diverse degrees in crowded cellular nanoenvironments. Especially, an average 17% copies of U1 glycoRNA of single cells are gathered in various nano environments on the cell surface. The strategy provides a powerful tool for digitally quantitative visualization of dense biomolecules below the spatial resolution of microscopies and can provide insights into underlying functions and mechanisms of the dense distribution information.

Proximity-activated DNA scanning encoded sequencing for massive access to membrane proteins nanoscale organization

Cellular structure maintenance and function regulation critically depend on the composition and spatial distribution of numerous membrane proteins. However, current methods face limitations in spatial coverage and data scalability, hindering the comprehensive analysis of protein interactions in complex cellular nanoenvironment. Herein, we introduce proximity-activated DNA scanning encoded sequencing (PADSE-seq), an innovative technique that utilizes flexible DNA probes with adjustable lengths. These dynamic probes are anchored at a single end, enabling free swings within a nanoscale range to perform global scanning, recording, and accumulating of information on diverse proximal proteins in random directions along unrestricted paths. PADSE-seq leverages the autonomous cyclic cleavage of single-stranded DNA to sequentially activate encoded probes distributed throughout the local area. This process triggers strand displacement amplification and bidirectional extension reactions, linking proteins barcodes with molecular barcodes in tandem and further generating millions to billions of amplicons embedded with the combinatorial identifiers for next-generation sequencing analysis. As a proof of concept, we validated PADSE-seq for mapping the distribution of over a dozen kinds of proteins, including HER1, EpCAM, and PDL1, in proximity to HER2 in breast cancer cell lines, demonstrating its ability to decode multiplexed protein proximities at the nanoscale. Notably, we observed that the spatial distribution of proximal proteins around low-abundance target proteins exhibited greater diversity across regions with variable proximity ranges. This method offers a massive access for high-resolution and comprehensive mapping of cellular molecular interactions, paving the way for deeper insights into complex biological processes and advancing the field of precision medicine.

A Primer-Regulated Rolling Circle Amplification (RCA) for Logic-Controlled Multiplexed Enzyme Analysis

DNA-related enzymes are associated with various diseases and have been potential biomarkers for clinical diagnosis. Developing robust and ultrasensitive methods is extremely favorable for the detection of these biomarkers. To this purpose, a primer-regulated rolling circle amplification (RCA) strategy was ingeniously proposed. Briefly, the RCA primer, which was invalidated with 3'-inverted dT (locked state) and unable to initiate an amplification reaction by phi29 DNA polymerase, was embedded with the recognition substrate of the specific enzyme. In the presence of the target, the recognition and cleavage process of the enzyme prompted the release of the 3'-inverted dT and the regeneration of 3'-OH (unlocked state), satisfying the vital prerequisite for RCA. By adopting this programmable and modular design, the recognition substrate can be either single base sites or a specific sequence for different types of enzymes. This also enables us to conduct single or multiple enzyme detection conveniently, relying on a logic-controlled manner including YES, OR, AND, and AND-OR operations. Overall, the proposed strategy is uniquely insightful and provides a universal tool for multiple analyses of diverse DNA-related enzymes.

Visualizing epigenetic modifications and their spatial proximities in single cells using three DNA-encoded amplifying FISH imaging strategies: BEA-FISH, PPDA-FISH and Cell-TALKING

Epigenetic modifications and spatial proximities of nucleic acids and proteins play important roles in regulating physiological processes and disease progression. Currently available cell imaging methods, such as fluorescence in situ hybridization (FISH) and immunofluorescence, struggle to detect low-abundance modifications and their spatial proximities. Here we describe a step-by-step protocol for three DNA-encoded amplifying FISH-based imaging strategies to overcome these challenges for varying applications: base-encoded amplifying FISH (BEA-FISH), pairwise proximity-differentiated amplifying FISH (PPDA-FISH) and cellular macromolecules-tethered DNA walking indexing (Cell-TALKING). They all use the similar core principle of DNA-encoded amplification, which transforms different nonsequence molecular features into unique DNA barcodes for in situ rolling circle amplification and FISH analysis. This involves three key reactions in fixed cell samples: target labeling, DNA encoding and rolling circle amplification imaging. Using this protocol, these three imaging strategies achieve in situ counting of low-abundance modifications alone, the pairwise proximity-differentiated visualization of two modifications and the exploration of multiple modifications around one protein (one-to-many proximity), respectively. Low-abundance modifications, including 5-hydroxymethylcytosine, 5-formylcytosine, 5-hydroxymethyluracil and 5-formyluracil, are clearly visualized in single cells. Various combinatorial patterns of nucleic acid modifications and/or histone modifications are found. The whole protocol takes ~2-4 d to complete, depending on different imaging applications.

Advanced Ligase Chain Reaction Strategy to Generate a Circular DNA Walker for Electrochemiluminescent Detection of Single Nucleotide Polymorphism

Single nucleotide polymorphism (SNP) primarily refers to DNA sequence polymorphism caused by variations in a single nucleotide, which is closely associated with many diseases such as genetic disorders and tumors. However, trace DNA mutants typically exist in a large pool of wild-type DNA, making it challenging to establish accurate and sensitive approaches for SNP detection. Herein, we developed an advanced ligase chain reaction (LCR) strategy to output the circular DNA walker for signal amplification, which realized accuracy and sensitive SNP detection based on the electrochemiluminescent (ECL) platform. Unlike the general LCR system that utilizes two sets of short single-stranded DNA (ssDNA) primers to generate double-stranded DNA amplification products, we ingeniously designed a long single-stranded DNA primer to replace one set of short ssDNA primers, allowing for the generation of circular DNA products upon complementing the target. Noticeably, the circular DNA serves as a DNA walker that can be easily purified by nucleases to eliminate unreacted primers and byproducts, significantly improving accuracy and sensitivity. Then, the circular DNA walker moved along a linearly ordered DNA quenching probe track modified on the ECL sensing interface, restoring the ECL signals by cleaving the quenching probes labeled on the DNA track with the help of apurinic/apyrimidinic endonuclease 1. Employing the p53 gene as a model, we realized the sensitive detection of mutant p53 in the range from 10 aM to 10 pM, with a detection limit of 6 aM, providing a promising platform for SNP detection.

Self-Replicating Catalytic Hybridization Assembly of Bipedal DNAzyme Walkers for Enhanced Electrochemiluminescence Bioanalysis

Dynamic DNA nanodevices, particularly DNA walkers, have proven to be versatile tools for target recognition, signal conversion, and amplification in biosensing. However, their ability to detect low-abundance analytes in complex biological samples is often compromised by limited amplification depth and severe signal leakage. To address these challenges, we developed a simple yet highly efficient strategy to engineer a self-replicating bipedal DNAzyme (SEDY) walker for sensitive and selective electrochemiluminescence (ECL) bioanalysis. Unlike conventional DNA walkers that are typically constructed by catalytic DNA assembly in a single direction, the SEDY walker integrates a self-replicating feedback mechanism that greatly enhances both the selectivity and sensitivity of bioanalysis. First, the SEDY walker is assembled through a target-triggered, enzyme-free, self-replicating catalytic approach, minimizing the risk of undesired side reactions and signal leakage by simplifying reactant complexity. Furthermore, the SEDY walker features newly exposed trigger sequences that facilitate its autonomous replication, leading to a robust and exponential amplification of its products. Our experiments demonstrate that the SEDY walker can sensitively and selectively detect acetamiprid by navigating specific probes within cross-shaped DNA orbits. The ECL biosensor offers a linear detection range from 1 × 10-15 M to 1 × 10-9 M, with a limit of detection as low as 5.8 × 10-16 M. We anticipate that the SEDY walker will be a powerful tool for detecting various analytes in biological applications.

Selective Ligase-Based Sample Processing-Free Discrimination and Detection of Site-Specific DNA 5-Hydroxymethylcytosine

Accurate detection of site-specific 5-hydroxymethylcytosine (5hmC) in genomic DNA is of great significance, but it is technically challenging to directly distinguish very low levels of 5hmC from their abundant cytosine/5-methylcytosine (C/5mC) analogues. Herein, we wish to propose a selective ligase-mediated mechanism (SLim) that can directly discriminate 5hmC from C/5mC with a high specificity without the use of any sample processing protocol. In this new design, we discovered that HiFi Taq DNA Ligase can well tolerate the mismatched 5hmC/A base-pairing and then effectively ligate the associated nicking site while the mismatched 5mC/A or C/A pairs cannot be recognized by HiFi Taq DNA Ligase, providing a new way for direct and selective discriminating 5hmC from its similar analogues. Ultrasensitive and selective quantification of site-specific 5hmC is realized by coupling the SLim with polymerase chain reaction (PCR) or loop-mediated isothermal amplification (LAMP).

Bidirectional linkage of DNA barcodes for the multiplexed mapping of higher-order protein interactions in cells

Capturing the full complexity of the diverse hierarchical interactions in the protein interactome is challenging. Here we report a DNA-barcoding method for the multiplexed mapping of pairwise and higher-order protein interactions and their dynamics within cells. The method leverages antibodies conjugated with barcoded DNA strands that can bidirectionally hybridize and covalently link to linearize closely spaced interactions within individual 3D protein complexes, encoding and decoding the protein constituents and the interactions among them. By mapping protein interactions in cancer cells and normal cells, we found that tumour cells exhibit a larger diversity and abundance of protein complexes with higher-order interactions. In biopsies of human breast-cancer tissue, the method accurately identified the cancer subtype and revealed that higher-order protein interactions are associated with cancer aggressiveness.

Molecular robotic agents that survey molecular landscapes for information retrieval

DNA-based artificial motors have allowed the recapitulation of biological functions and the creation of new features. Here, we present a molecular robotic system that surveys molecular environments and reports spatial information in an autonomous and repeated manner. A group of molecular agents, termed 'crawlers', roam around and copy information from DNA-labeled targets, generating records that reflect their trajectories. Based on a mechanism that allows random crawling, we show that our system is capable of counting the number of subunits in example molecular complexes. Our system can also detect multivalent proximities by generating concatenated records from multiple local interactions. We demonstrate this capability by distinguishing colocalization patterns of three proteins inside fixed cells under different conditions. These mechanisms for examining molecular landscapes may serve as a basis towards creating large-scale detailed molecular interaction maps inside the cell with nanoscale resolution.

Universal Signal Switch Based on a Mesostructured Silica Xerogel-Confined ECL Polymer for Epigenetic Quantification

The development of a highly accurate electrochemiluminescence (ECL) signal switch to avoid nonspecific stimulus responses is currently a significant and challenging task. Here, we constructed a universal signal switch utilizing a luminophore-quencher pair of mesostructured silica xerogel-confined polymer and gold nanoparticles (Au NPs) that can accurately detect low-abundance epigenetic markers in complex sample systems. Notably, the ECL polymer encapsulated in mesostructured silica xerogel acts as a luminophore, which demonstrated a highly specific dependence on the Au NPs-mediated energy transfer quenching. To demonstrate the feasibility, we specifically labeled the 5-hydroxymethylcytosine (5hmC) site on the random sequence using a double-stranded (dsDNA) tag that was skillfully designed with the CRISPR/Cas12a activator and recombinant polymerase amplification (RPA) template. After amplification by RPA, a large amount of dsDNA tag was generated as the activator to initiate the trans-cleavage activity of CRISPR/Cas12a and subsequently activate the signal switch, allowing for precise quantification of 5hmC. The ECL signal switch improves the stability of the luminophore and prevents nonspecific stimulus responses, providing a new paradigm for constructing high-precision biosensors.

Development of a DNAzyme Walker for the Detection of APE1 in Living Cancer Cells

DNAzyme walker technology is a compelling option for bioanalytical and drug delivery applications. While nucleic acid and protein targets have been used to activate DNAzyme walkers, investigations into enzyme-triggered DNAzyme walkers in living cells are still in their early stages. The base excision repair (BER) pathway presents an array of enzymes that are overexpressed in cancer cells. Here, we introduce a DNAzyme walker system that sensitively and specifically detects the BER enzyme apurinic/apyrimidinic endodeoxyribonuclease 1 (APE1). We constructed the DNAzyme walker on the surface of 20 nm-diameter gold nanoparticles. We achieved a detection limit of 160 fM of APE1 in a buffer and in whole cell lysate equivalent to the amount of APE1 in a single HeLa cell in a sample volume of 100 μL. Confocal imaging of the DNAzyme walking reveals a cytoplasmic distribution of APE1 in HeLa cells. Walking activity is tunable to exogenous Mn2+ concentrations and the uptake of the DNAzyme walker system does not require transfection assistance. We demonstrate the investigative potential of the DNAzyme walker for up-regulated or overactive enzyme biomarkers of the BER pathway in cancer cells.

Hierarchical DNA branch assembly-encoded fluorescent nanoladders for single-cell transcripts imaging

Spatial visualization of single-cell transcripts is limited by signal specificity and multiplexing. Here, we report hierarchical DNA branch assembly-encoded fluorescent nanoladders, which achieve denoised and highly multiplexed signal amplification for single-molecule transcript imaging. This method first offers independent RNA-primed rolling circle amplification without nonspecific amplification based on circular DNAzyme. It then executes programmable DNA branch assembly on these amplicons to encode virtual signals for visualizing numbers of targets by FISH. In theory, more virtual signals can be encoded via the increase of detection spectral channels and repeats of the same sequences on barcode. Our method almost eliminates nonspecific amplification in fixed cells (reducing nonspecific spots of single cells from 16 to nearly zero), and achieves simultaneous quantitation of nine transcripts by using only two detection spectral channels. We demonstrate accurate RNA profiling in different cancer cells, and reveal diverse localization patterns for spatial regulation of transcripts.

Branched immunochip-integrated pairwise barcoding amplification exploring the spatial proximity of two post-translational modifications in distinct cell subpopulations

Investigating the spatial information of post-translational modifications (PTMs) in distinct cell subpopulations represents a new direction toward single-cell analysis. The specific capture of cell populations combined with PTM spatial proximity visualization making it practically challenging. Here, we develop branched immunochip-integrated pairwise barcoding amplification, termed biChip-PBA, which can perform the respective capture of cell subpopulations expressing different membrane proteins and successive PBA-based fluorescence imaging of PTM proximities. Our work may provide multilevel information for new insights into epigenetic regulation and cell function.

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.

Spatially Resolved, Error-Robust Multiplexed MicroRNA Profiling in Single Living Cells

Simultaneous imaging of multiple microRNAs (miRNAs) in individual living cells is challenging due to the lack of spectrally distinct encoded fluorophores and non-cytotoxic methods. We describe a multiplexed error-robust combinatorial fluorescent label-encoding method, termed fluorophores encoded error-corrected labels (FluoELs), enabling multiplexed miRNA imaging in living cells with error-correcting capability. The FluoELs comprise proportional dual fluorophores for encoding and a constant quantitative single fluorophore for error-corrected quantification. Both are embedded in 260 nm core-shell silica nanoparticles modified with molecular beacon detection probes. The FluoELs are low cytotoxic and could accurately quantify and spatially resolve nine breast-cancer-related miRNAs and evaluate their coordination. The FluoELs enabled a single-cell analysis platform to evaluate miRNA expression profiles and the molecular mechanisms underlying miRNA-associated diseases.

Role of main RNA modifications in cancer: N6-methyladenosine, 5-methylcytosine, and pseudouridine

Cancer is one of the major diseases threatening human life and health worldwide. Epigenetic modification refers to heritable changes in the genetic material without any changes in the nucleic acid sequence and results in heritable phenotypic changes. Epigenetic modifications regulate many biological processes, such as growth, aging, and various diseases, including cancer. With the advancement of next-generation sequencing technology, the role of RNA modifications in cancer progression has become increasingly prominent and is a hot spot in scientific research. This review studied several common RNA modifications, such as N⁶-methyladenosine, 5-methylcytosine, and pseudouridine. The deposition and roles of these modifications in coding and noncoding RNAs are summarized in detail. Based on the RNA modification background, this review summarized the expression, function, and underlying molecular mechanism of these modifications and their regulators in cancer and further discussed the role of some existing small-molecule inhibitors. More in-depth studies on RNA modification and cancer are needed to broaden the understanding of epigenetics and cancer diagnosis, treatment, and prognosis.

Applications of DNA-Functionalized Proteins

As an important component that constitutes all the cells and tissues of the human body, protein is involved in most of the biological processes. Inspired by natural protein systems, considerable efforts covering many discipline fields were made to design artificial protein assemblies and put them into application in recent decades. The rapid development of structural DNA nanotechnology offers significant means for protein assemblies and promotes their application. Owing to the programmability, addressability and accurate recognition ability of DNA, many protein assemblies with unprecedented structures and improved functions have been successfully fabricated, consequently creating many brand-new researching fields. In this review, we briefly introduced the DNA-based protein assemblies, and highlighted the limitations in application process and corresponding strategies in four aspects, including biological catalysis, protein detection, biomedicine treatment and other applications.

Antibody-Responsive Ratiometric Fluorescence Biosensing of Biemissive Silver Nanoclusters Wrapped in Switchable DNA Tweezers

Exploring the ratiometric fluorescence biosensing of DNA-templated biemissive silver nanoclusters (AgNCs) is significant in bioanalysis, yet the design of a stimuli-responsive DNA device is a challenge. Herein, using the anti-digoxin antibody (anti-Dig) with two identical binding sites as a model, a tweezer-like DNA architecture is assembled to populate fluorescent green- and red-AgNCs (g-AgNCs and r-AgNCs), aiming to produce a ratio signal via specific recognition of anti-Dig with two haptens (DigH). To this end, four DNA probes are programmed, including a reporter strand (RS) dually ended with a g-/r-AgNC template sequence, an enhancer strand (ES) tethering two same G-rich tails (G18), a capture strand (CS) labeled with DigH at two ends, and a help strand (HS). Initially, both g-AgNCs and r-AgNCs wrapped in the intact RS are nonfluorescent, whereas the base pairing between RS, ES, CS, and HS resulted in the construction of DNA mechanical tweezers with two symmetric arms hinged by a rigid "fulcrum", in which g-AgNCs are lighted up due to G18 proximity ("green-on"), and r-AgNCs away from G18 are still dark ("red-off"). When two DigHs in proximity recognize and bind anti-Dig, the conformation switch of these tweezers resultantly occurs, taking g-AgNCs away from G18 for "green-off" and bringing r-AgNCs close to G18 for "red-on". As such, the ratiometric fluorescence of r-AgNCs versus g-AgNCs is generated in response to anti-Dig, achieving reliable quantization with a limit of detection at the picomolar level. Based on the fast stimulated switch of unique DNA tweezers, our ratiometric strategy of dual-emitting AgNCs would provide a new avenue for a variety of bioassays.

Bioorthogonal Chemical Signature Enabling Amplified Visualization of Cellular Oxidative Thymines

Cellular oxidative thymines, 5-hydroxymethyluracil (5hmU) and 5-formyluracil (5fU), are found in the genomes of a diverse range of organisms, the distribution of which profoundly influence biological processes and living systems. However, the distribution of cellular oxidative thymines has not been explored because of lacking both specific bioorthogonal labeling and sensitivity methods for single-cell analysis. Herein, we report a bioorthogonal chemical signature enabling amplified visualization of cellular oxidative thymines in single cells. The synthesized ATP-γ-alkyne, an ATP analogue with bioorthogonal tag modified on γ-phosphate can be specifically linked to cellular 5hmU by chemoenzymatic labeling. DNA with 5-alkynephosphomethyluracil were then clicked with azide (N₃)-modified 5hmU-primer. Identification of 5fU is based on selective reduction from 5fU to 5hmU, subsequent chemoenzymatic labeling of the newly generated 5hmU, and cross-linking with N₃-modified 5fU-primer via click chemistry. Then, all of the 5hmU and 5fU sites are encoded with respective circularized barcodes. These barcodes are simultaneously amplified for multiplexed single-molecule imaging. The above two kinds of barcodes can be simultaneously amplified for differentiated visualization of 5hmU and 5fU in single cells. We find these two kinds of cellular oxidative thymines are spatially organized in a cell-type-dependent style with cell-to-cell heterogeneity. We also investigate their multilevel subcellular information and explore their dynamic changes during cell cycles. Further, using DNA sequencing instead of fluorescence imaging, our proposed bioorthogonal chemical signature holds great potential to offer the sequence information of these oxidative thymines in cells and may provide a reliable chemical biology approach for studying the whole-genome oxidative thymines profiles and insights into their functional role and dynamics in biology.