Nonaqueous Oxidation in DNA Microarray Synthesis Improves the Oligonucleotide Quality and Preserves Surface Integrity on Gold and Indium Tin Oxide Substrates.

Nucleic acids attached to electrically conductive surfaces are very frequently used platforms for sensing and analyte detection as well as for imaging. Synthesizing DNA on these uncommon substrates and preserving the conductive layer is challenging as this coating tends to be damaged by the repeated use of iodine and water, which is the standard oxidizing medium following phosphoramidite coupling. Here, we thoroughly investigate the use of camphorsulfonyl oxaziridine (CSO), a nonaqueous alternative to I2/H2O, for the synthesis of DNA microarrays in situ. We find that CSO performs equally well in producing high hybridization signals on glass microscope slides, and CSO also protects the conductive layer on gold and indium tin oxide (ITO)-coated slides. DNA synthesis on conductive substrates with CSO oxidation yields microarrays of quality approaching that of conventional glass with intact physicochemical properties.

Dipodal Silanes Greatly Stabilize Glass Surface Functionalization for DNA Microarray Synthesis and High-Throughput Biological Assays.

Glass is by far the most common substrate for biomolecular arrays, including high-throughput sequencing flow cells and microarrays. The native glass hydroxyl surface is modified by using silane chemistry to provide appropriate functional groups and reactivities for either in situ synthesis or surface immobilization of biologically or chemically synthesized biomolecules. These arrays, typically of oligonucleotides or peptides, are then subjected to long incubation times in warm aqueous buffers prior to fluorescence readout. Under these conditions, the siloxy bonds to the glass are susceptible to hydrolysis, resulting in significant loss of biomolecules and concomitant loss of signal from the assay. Here, we demonstrate that functionalization of glass surfaces with dipodal silanes results in greatly improved stability compared to equivalent functionalization with standard monopodal silanes. Using photolithographic in situ synthesis of DNA, we show that dipodal silanes are compatible with phosphoramidite chemistry and that hybridization performed on the resulting arrays provides greatly improved signal and signal-to-noise ratios compared with surfaces functionalized with monopodal silanes.

Chemical and photochemical error rates in light-directed synthesis of complex DNA libraries.

Nucleic acid microarrays are the only tools that can supply very large oligonucleotide libraries, cornerstones of the nascent fields of de novo gene assembly and DNA data storage. Although the chemical synthesis of oligonucleotides is highly developed and robust, it is not error free, requiring the design of methods that can correct or compensate for errors, or select for high-fidelity oligomers. However, outside the realm of array manufacturers, little is known about the sources of errors and their extent. In this study, we look at the error rate of DNA libraries synthesized by photolithography and dissect the proportion of deletion, insertion and substitution errors. We find that the deletion rate is governed by the photolysis yield. We identify the most important substitution error and correlate it to phosphoramidite coupling. Besides synthetic failures originating from the coupling cycle, we uncover the role of imperfections and limitations related to optics, highlight the importance of absorbing UV light to avoid internal reflections and chart the dependence of error rate on both position on the array and position within individual oligonucleotides. Being able to precisely quantify all types of errors will allow for optimal choice of fabrication parameters and array design.

Gastric Serotonin Biosynthesis and Its Functional Role in L-Arginine-Induced Gastric Proton Secretion.

Among mammals, serotonin is predominantly found in the gastrointestinal tract, where it has been shown to participate in pathway-regulating satiation. For the stomach, vascular serotonin release induced by gastric distension is thought to chiefly contribute to satiation after food intake. However, little information is available on the capability of gastric cells to synthesize, release and respond to serotonin by functional changes of mechanisms regulating gastric acid secretion. We investigated whether human gastric cells are capable of serotonin synthesis and release. First, HGT-1 cells, derived from a human adenocarcinoma of the stomach, and human stomach specimens were immunostained positive for serotonin. In HGT-1 cells, incubation with the tryptophan hydroxylase inhibitor p-chlorophenylalanine reduced the mean serotonin-induced fluorescence signal intensity by 27%. Serotonin release of 147 ± 18%, compared to control HGT-1 cells (set to 100%) was demonstrated after treatment with 30 mM of the satiating amino acid L-Arg. Granisetron, a 5-HT3 receptor antagonist, reduced this L-Arg-induced serotonin release, as well as L-Arg-induced proton secretion. Similarly to the in vitro experiment, human antrum samples released serotonin upon incubation with 10 mM L-Arg. Overall, our data suggest that human parietal cells in culture, as well as from the gastric antrum, synthesize serotonin and release it after treatment with L-Arg via an HTR3-related mechanism. Moreover, we suggest not only gastric distension but also gastric acid secretion to result in peripheral serotonin release.

l-DNA Duplex Formation as a Bioorthogonal Information Channel in Nucleic Acid-Based Surface Patterning.

Photolithographic in situ synthesis of nucleic acids enables extremely high oligonucleotide sequence density as well as complex surface patterning and combined spatial and molecular information encoding. No longer limited to DNA synthesis, the technique allows for total control of both chemical and Cartesian space organization on surfaces, suggesting that hybridization patterns can be used to encode, display or encrypt informative signals on multiple chemically orthogonal levels. Nevertheless, cross-hybridization reduces the available sequence space and limits information density. Here we introduce an additional, fully independent information channel in surface patterning with in situ l-DNA synthesis. The bioorthogonality of mirror-image DNA duplex formation prevents both cross-hybridization on chimeric l-/d-DNA microarrays and also results in enzymatic orthogonality, such as nuclease-proof DNA-based signatures on the surface. We show how chimeric l-/d-DNA hybridization can be used to create informative surface patterns including QR codes, highly counterfeiting resistant authenticity watermarks, and concealed messages within high-density d-DNA microarrays.

Caffeine induces gastric acid secretion via bitter taste signaling in gastric parietal cells.

Caffeine, generally known as a stimulant of gastric acid secretion (GAS), is a bitter-tasting compound that activates several taste type 2 bitter receptors (TAS2Rs). TAS2Rs are expressed in the mouth and in several extraoral sites, e.g., in the gastrointestinal tract, in which their functional role still needs to be clarified. We hypothesized that caffeine evokes effects on GAS by activation of oral and gastric TAS2Rs and demonstrate that caffeine, when administered encapsulated, stimulates GAS, whereas oral administration of a caffeine solution delays GAS in healthy human subjects. Correlation analysis of data obtained from ingestion of the caffeine solution revealed an association between the magnitude of the GAS response and the perceived bitterness, suggesting a functional role of oral TAS2Rs in GAS. Expression of TAS2Rs, including cognate TAS2Rs for caffeine, was shown in human gastric epithelial cells of the corpus/fundus and in HGT-1 cells, a model for the study of GAS. In HGT-1 cells, various bitter compounds as well as caffeine stimulated proton secretion, whereby the caffeine-evoked effect was (i) shown to depend on one of its cognate receptor, TAS2R43, and adenylyl cyclase; and (ii) reduced by homoeriodictyol (HED), a known inhibitor of caffeine's bitter taste. This inhibitory effect of HED on caffeine-induced GAS was verified in healthy human subjects. These findings (i) demonstrate that bitter taste receptors in the stomach and the oral cavity are involved in the regulation of GAS and (ii) suggest that bitter tastants and bitter-masking compounds could be potentially useful therapeutics to regulate gastric pH.

Large-Scale Photolithographic Synthesis of Chimeric DNA/RNA Hairpin Microarrays To Explore Sequence Specificity Landscapes of RNase HII Cleavage.

Ribonuclease HII (RNase HII) is an essential endoribonuclease that binds to double-stranded DNA with RNA nucleotide incorporations and cleaves 5' of the ribonucleotide at RNA-DNA junctions. Thought to be present in all domains of life, RNase HII protects genomic integrity by initiating excision repair pathways that protect the encoded information from rapid degradation. There is sparse evidence that the enzyme cleaves some substrates better than others, but a large-scale study is missing. Such large-scale studies can be carried out on microarrays, and we employ chemical photolithography to synthesize very large combinatorial libraries of fluorescently labeled DNA/RNA chimeric sequences that self-anneal to form hairpin structures that are substrates for Escherichia coli RNase HII. The relative activity is determined by the loss of fluorescence upon cleavage. Each substrate includes a double-stranded 5 bp variable region with one to five consecutive ribonucleotide substitutions. We also examined the effect of all possible single and double mismatches, for a total of >9500 unique structures. Differences in cleavage efficiency indicate some level of substrate preference, and we identified the 5'-dC/rC-rA-dX-3' motif in well-cleaved substrates. The results significantly extend known patterns of RNase HII sequence specificity and serve as a template using large-scale photolithographic synthesis to comprehensively map landscapes of substrate specificity of nucleic acid-processing enzymes.

Mapping the affinity landscape of Thrombin-binding aptamers on 2΄F-ANA/DNA chimeric G-Quadruplex microarrays.

In situ fabricated nucleic acids microarrays are versatile and very high-throughput platforms for aptamer optimization and discovery, but the chemical space that can be probed against a given target has largely been confined to DNA, while RNA and non-natural nucleic acid microarrays are still an essentially uncharted territory. 2΄-Fluoroarabinonucleic acid (2΄F-ANA) is a prime candidate for such use in microarrays. Indeed, 2΄F-ANA chemistry is readily amenable to photolithographic microarray synthesis and its potential in high affinity aptamers has been recently discovered. We thus synthesized the first microarrays containing 2΄F-ANA and 2΄F-ANA/DNA chimeric sequences to fully map the binding affinity landscape of the TBA1 thrombin-binding G-quadruplex aptamer containing all 32 768 possible DNA-to-2΄F-ANA mutations. The resulting microarray was screened against thrombin to identify a series of promising 2΄F-ANA-modified aptamer candidates with Kds significantly lower than that of the unmodified control and which were found to adopt highly stable, antiparallel-folded G-quadruplex structures. The solution structure of the TBA1 aptamer modified with 2΄F-ANA at position T3 shows that fluorine substitution preorganizes the dinucleotide loop into the proper conformation for interaction with thrombin. Overall, our work strengthens the potential of 2΄F-ANA in aptamer research and further expands non-genomic applications of nucleic acids microarrays.

Exposure of Human Gastric Cells to Oxidized Lipids Stimulates Pathways of Amino Acid Biosynthesis on a Genomic and Metabolomic Level.

The Western diet is characterized by a high consumption of heat-treated fats and oils. During deep-frying processes, vegetable oils are subjected to high temperatures which result in the formation of lipid peroxidation products. Dietary intake of oxidized vegetable oils has been associated with various biological effects, whereas knowledge about the effects of structurally-characterized lipid peroxidation products and their possible absorption into the body is scarce. This study investigates the impact of linoleic acid, one of the most abundant polyunsaturated fatty acids in vegetable oils, and its primary and secondary peroxidation products, 13-HpODE and hexanal, on genomic and metabolomic pathways in human gastric cells (HGT-1) in culture. The genomic and metabolomic approach was preceded by an up-to-six-hour exposure study applying 100 µM of each test compound to the apical compartment in order to quantitate the compounds' recovery at the basolateral side. Exposure of HGT-1 cells to either 100 µM linoleic acid or 100 µM 13-HpODE resulted in the formation of approximately 1 µM of the corresponding hydroxy fatty acid, 13-HODE, in the basolateral compartment, whereas a mean concentration of 0.20 ± 0.13 µM hexanal was quantitated after an equivalent application of 100 µM hexanal. An integrated genomic and metabolomic pathway analysis revealed an impact of the linoleic acid peroxidation products, 13-HpODE and hexanal, primarily on pathways related to amino acid biosynthesis (p < 0.05), indicating that peroxidation of linoleic acid plays an important role in the regulation of intracellular amino acid biosynthesis.

The advanced glycation end product Nϵ -carboxymethyllysine and its precursor glyoxal increase serotonin release from Caco-2 cells.

Advanced glycation end products (AGEs), comprising a highly diverse class of Maillard reaction compounds formed in vivo and during heating processes of foods, have been described in the progression of several degenerative conditions such as Alzheimer's disease and diabetes mellitus. Nϵ -Carboxymethyllysine (CML) represents a well-characterized AGE, which is frequently encountered in a Western diet and is known to mediate its cellular effects through binding to the receptor for AGEs (RAGE). As very little is known about the impact of exogenous CML and its precursor, glyoxal, on intestinal cells, a genome-wide screening using a customized microarray was conducted in fully differentiated Caco-2 cells. After verification of gene regulation by qPCR, functional assays on fatty acid uptake, glucose uptake, and serotonin release were performed. While only treatment with glyoxal showed a slight impact on fatty acid uptake (P < 0.05), both compounds reduced glucose uptake significantly, leading to values of 81.3% ± 22.8% (500 µM CML, control set to 100%) and 68.3% ± 20.9% (0.3 µM glyoxal). Treatment with 500 µM CML or 0.3 µM glyoxal increased serotonin release (P < 0.05) to 236% ± 111% and 264% ± 66%, respectively. Co-incubation with the RAGE antagonist FPS-ZM1 reduced CML-induced serotonin release by 34%, suggesting a RAGE-mediated mechanism. Similarly, co-incubation with the SGLT-1 inhibitor phloridzin attenuated serotonin release after CML treatment by 32%, hinting at a connection between CML-stimulated serotonin release and glucose uptake. Future studies need to elucidate whether the CML/glyoxal-induced serotonin release in enterocytes might stimulate serotonin-mediated intestinal motility.

High-Density RNA Microarrays Synthesized In†Situ by Photolithography.

While high-density DNA microarrays have been available for over three decades, the synthesis of equivalent RNA microarrays has proven intractable until now. Herein we describe the first in situ synthesis of mixed-based, high-density RNA microarrays using photolithography and light-sensitive RNA phosphoramidites. With coupling efficiencies comparable to those of DNA monomers, RNA oligonucleotides at least 30 nucleotides long can now efficiently be prepared using modified phosphoramidite chemistry. A two-step deprotection route unmasks the phosphodiester, the exocyclic amines and the 2' hydroxyl. Hybridization and enzymatic assays validate the quality and the identity of the surface-bound RNA. We show that high-density is feasible by synthesizing a complex RNA permutation library with 262144 unique sequences. We also introduce DNA/RNA chimeric microarrays and explore their applications by mapping the sequence specificity of RNase HII.

N(ϵ) -Carboxymethyllysine Increases the Expression of miR-103/143 and Enhances Lipid Accumulation in 3T3-L1 Cells.

Advanced glycation endproducts, formed in vivo, but also by the Maillard reaction upon thermal treatment of foods, have been associated with the progression of pathological conditions such as diabetes mellitus. In addition to the accumulation with age, exogenous AGEs are introduced into the circulation from dietary sources. In this study, we investigated the effects of addition of free N(ϵ) -carboxymethyllysine (CML), a well-characterized product of the Maillard reaction, on adipogenesis in 3T3-L1 preadipocytes. Treatment with 5, 50, or 500 µM CML resulted in increased lipid accumulation to similar extents, by 11.5 ± 12.6%, 12.9 ± 8.6%, and 12.8 ± 8.5%, respectively. Long-term treatment with 500 µM CML during adipogenesis resulted in increases in miR-103 and miR-143 levels, two miRNAs described to be involved in impaired glucose homeostasis and increased lipid accumulation. Furthermore, the expression of genes associated with these miRNAs, consisting of Akt1, PI3k, and Cav1 was regulated by CML. Short-term treatment of mature 3T3-L1 adipocytes with CML resulted in decreased basal glucose uptake. These results, indicate that the addition of protein-free CML to 3T3-L1 cells influence parameters associated with adipogenesis and glucose homeostasis at transcriptional, and functional level; this indicates that free CML derived from exogenous sources, in addition to protein-bound CML may be relevant in this context. J. Cell. Biochem. 117: 2413-2422, 2016. © 2016 The Authors. Journal of Cellular Biochemistry Published by Wiley Periodicals, Inc.

Sequence-Dependent Fluorescence of Cy3- and Cy5-Labeled Double-Stranded DNA.

The fluorescent intensity of Cy3 and Cy5 dyes is strongly dependent on the nucleobase sequence of the labeled oligonucleotides. Sequence-dependent fluorescence may significantly influence the data obtained from many common experimental methods based on fluorescence detection of nucleic acids, such as sequencing, PCR, FRET, and FISH. To quantify sequence dependent fluorescence, we have measured the fluorescence intensity of Cy3 and Cy5 bound to the 5' end of all 1024 possible double-stranded DNA 5mers. The fluorescence intensity was also determined for these dyes bound to the 5' end of fixed-sequence double-stranded DNA with a variable sequence 3' overhang adjacent to the dye. The labeled DNA oligonucleotides were made using light-directed, in situ microarray synthesis. The results indicate that the fluorescence intensity of both dyes is sensitive to all five bases or base pairs, that the sequence dependence is stronger for double- (vs single-) stranded DNA, and that the dyes are sensitive to both the adjacent dsDNA sequence and the 3'-ssDNA overhang. Purine-rich sequences result in higher fluorescence. The results can be used to estimate measurement error in experiments with fluorescent-labeled DNA, as well as to optimize the fluorescent signal by considering the nucleobase environment of the labeling cyanine dye.

Express photolithographic DNA microarray synthesis with optimized chemistry and high-efficiency photolabile groups.

BACKGROUND: DNA microarrays are a core element of modern genomics research and medical diagnostics, allowing the simple and simultaneous determination of the relative abundances of hundreds of thousands to millions of genomic DNA or RNA sequences in a sample. Photolithographic in situ synthesis, using light projection from a digitally-controlled array of micromirrors, has been successful at both commercial and laboratory scales. The advantages of this synthesis method are its ability to reliably produce high-quality custom microarrays with a very high spatial density of DNA features using a compact device with few moving parts. The phosphoramidite chemistry used in photolithographic synthesis is similar to that used in conventional solid-phase synthesis of oligonucleotides, but some unique differences require an independent optimization of the synthesis chemistry to achieve fast and low-cost synthesis without compromising microarray quality. RESULTS: High microarray quality could be maintained while reducing coupling time to a few seconds using DCI activator. Five coupling activators were compared, which resulted in microarray hybridization signals following the order ETT > Activator 42 > DCI â‰« BTT â‰« pyridinium chloride, but only the use of DCI led to both high signal and highly uniform feature intensities. The photodeprotection time was also reduced to a few seconds by replacing the NPPOC photolabile group with the new thiophenyl-NPPOC group. Other chemical parameters, such as oxidation and washing steps were also optimized. CONCLUSIONS: Highly optimized and microarray-specific phosphoramidite chemistry, along with the use of the very photosensitive thiophenyl-NPPOC protecting group allow for the synthesis of high-complexity DNA arrays using coupling times of 15 s and deprotection times of 9 s. The resulting overall cycle time (coupling to coupling) of about 50 s, results in a three-fold reduction in synthesis time.

Nonivamide enhances miRNA let-7d expression and decreases adipogenesis PPARγ expression in 3T3-L1 cells.

Red pepper and its major pungent principle, capsaicin (CAP), have been shown to be effective anti-obesity agents by reducing energy intake, enhancing energy metabolism, decreasing serum triacylglycerol content, and inhibiting adipogenesis via activation of the transient receptor potential cation channel subfamily V member 1 (TRPV1). However, the binding of CAP to the TRPV1 receptor is also responsible for its pungent sensation, strongly limiting its dietary intake. Here, the effects of a less pungent structural CAP-analog, nonivamide, on adipogenesis and underlying mechanisms in 3T3-L1 cells were studied. Nonivamide was found to reduce mean lipid accumulation, a marker of adipogenesis, to a similar extent as CAP, up to 10.4% (P < 0.001). Blockage of the TRPV1 receptor with the specific inhibitor trans-tert-butylcyclohexanol revealed that the anti-adipogenic activity of nonivamide depends, as with CAP, on TRPV1 receptor activation. In addition, in cells treated with nonivamide during adipogenesis, protein levels of the pro-adipogenic transcription factor peroxisome-proliferator activated receptor γ (PPARγ) decreased. Results from miRNA microarrays and digital droplet PCR analysis demonstrated an increase in the expression of the miRNA mmu-let-7d-5p, which has been associated with decreased PPARγ levels.

Next-Generation o-Nitrobenzyl Photolabile Groups for Light-Directed Chemistry and Microarray Synthesis.

Light as an external trigger is a valuable and easily controllable tool for directing chemical reactions with high spatial and temporal accuracy. Two o-nitrobenzyl derivatives, benzoyl- and thiophenyl-NPPOC, undergo photo-deprotection with significantly improved efficiency over that of the commonly used NPPOC group. The two- and twelvefold increase in photo-deprotection efficiency was proven using photolithograph synthesis of microarrays.

Impaired metal perception and regulation of associated human foliate papillae tongue transcriptome in long-COVID-19.

Chemosensory impairment is an outstanding symptom of SARS-CoV-2 infections. We hypothesized that measured sensory impairments are accompanied by transcriptomic changes in the foliate papillae area of the tongue. Hospital personnel with known SARS-CoV-2 immunoglobulin G (IgG) status completed questionnaires on sensory perception (n = 158). A subcohort of n = 141 participated in forced choice taste tests, and n = 43 participants consented to donate tongue swabs of the foliate papillae area for whole transcriptome analysis. The study included four groups of participants differing in IgG levels (≥ 10 AU/mL = IgG+; < 10 AU/mL = IgG-) and self-reported sensory impairment (SSI±). IgG+ subjects not detecting metallic taste had higher IgG+ levels than IgG+ participants detecting iron gluconate (p = 0.03). Smell perception was the most impaired biological process in the transcriptome data from IgG+/SSI+ participants subjected to gene ontology enrichment. IgG+/SSI+ subjects demonstrated lower expression levels of 166 olfactory receptors (OR) and 9 taste associated receptors (TAS) of which OR1A2, OR2J2, OR1A1, OR5K1 and OR1G1, as well as TAS2R7 are linked to metallic perception. The question raised by this study is whether odorant receptors on the tongue (i) might play a role in metal sensation, and (ii) are potential targets for virus-initiated sensory impairments, which needs to be investigated in future functional studies.

Simultaneous light-directed synthesis of mirror-image microarrays in a photochemical reaction cell with flare suppression.

The use of photolabile protecting groups is a versatile and well-established means of synthesizing high complexity microarrays of biopolymers, such as nucleic acids and peptides, for high-throughput analysis. The synthesis takes place in a photochemical reaction cell which positions the microarray substrate at the focus of the optical system delivering the light and which can be connected to a fluidics system which delivers appropriate reagents to the surface in synchrony with the light exposure. Here we describe a novel photochemical reaction cell which allows for the simultaneous synthesis of microarrays on two substrates. The reaction cell positions both substrates within the limited depth-of-focus of the optical system while maintaining the necessary reagent flow conditions. The resulting microarrays are mirror images of each other but otherwise essentially identical. The new reaction cell doubles the throughput of microarray synthesis without increasing the consumption of reagents. In addition, a secondary flow chamber behind the reaction cell can be filled with an absorbent and index-matching fluid to eliminate reflections from light exiting the reaction cell assembly, greatly reducing unintended light exposure that reduces the sequence fidelity of the microarray probes.

Optimized light-directed synthesis of aptamer microarrays.

Aptamer microarrays are a promising high-throughput method for ultrasensitive detection of multiple analytes, but although much is known about the optimal synthesis of oligonucleotide microarrays used in hybridization-based genomics applications, the bioaffinity interactions between aptamers and their targets is qualitatively different and requires significant changes to synthesis parameters. Focusing on streptavidin-binding DNA aptamers, we employed light-directed in situ synthesis of microarrays to analyze the effects of sequence fidelity, linker length, surface probe density, and substrate functionalization on detection sensitivity. Direct comparison with oligonucleotide hybridization experiments indicates that aptamer microarrays are significantly more sensitive to sequence fidelity and substrate functionalization and have different optimal linker length and surface probe density requirements. Whereas microarray hybridization probes generate maximum signal with multiple deletions, aptamer sequences with the same deletion rate result in a 3-fold binding signal reduction compared with the same sequences synthesized for maximized sequence fidelity. The highest hybridization signal was obtained with dT 5mer linkers, and the highest aptamer signal was obtained with dT 11mers, with shorter aptamer linkers significantly reducing the binding signal. The probe hybridization signal was found to be more sensitive to molecular crowding, whereas the aptamer probe signal does not appear to be constrained within the density of functional surface groups commonly used to synthesize microarrays.

Enzymatic Synthesis of High-Density RNA Microarrays.

Oligonucleotide microarrays are used to investigate the interactome of nucleic acids. DNA microarrays are commercially available, whereas equivalent RNA microarrays are not. This protocol describes a method to convert DNA microarrays of any density and complexity into RNA microarrays using only readily available materials and reagents. This simple conversion protocol will facilitate the accessibility of RNA microarrays to a wide range of researchers. In addition to general considerations for the design of a template DNA microarray, this procedure describes the experimental steps of hybridization of an RNA primer to the immobilized DNA, followed by its covalent attachment via psoralen-mediated photocrosslinking. The subsequent enzymatic processing steps comprise the extension of the primer with T7 RNA polymerase to generate complementary RNA, and finally the removal of the DNA template with TURBO DNase. Beyond the conversion process, we also describe approaches to detect the RNA product either by internal labeling with fluorescently labeled NTPs or via hybridization to the product strand, a step that can then be complemented by an RNase H assay to confirm the nature of the product. © 2023 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Conversion of a DNA microarray to an RNA microarray Alternate Protocol: Detection of RNA via incorporation of Cy3-UTP Support Protocol 1: Detection of RNA via hybridization Support Protocol 2: RNase H assay.