RNA fluorescence in situ hybridization using 3-cyanovinylcarbazole modified oligodeoxyribonucleotides as photo-cross-linkable probes

Optogenetic Tools for Regulating RNA Metabolism and Functions

RNA molecules play a vital role in linking genetic information with various cellular processes. In recent years, a variety of optogenetic tools have been engineered for regulating cellular RNA metabolism and functions. These highly desirable tools can offer non-intrusive control with spatial precision, remote operation, and biocompatibility. Here, we would like to review these currently available approaches that can regulate RNAs with light: from non-genetically encodable chemically modified oligonucleotides to genetically encoded RNA aptamers that recognize photosensitive small-molecule or protein ligands. Some key applications of these optogenetic tools will also be highlighted to illustrate how they have been used for regulating all aspects of the RNA life cycle: from RNA synthesis, maturation, modification, and translation to their degradation, localization, and phase separation control. Some current challenges and potential practical utilizations of these RNA optogenetic tools will also be discussed.

Hybridization-specific chemical reactions to create interstrand crosslinking and threaded structures of nucleic acids

The interstrand crosslinking and threaded structures of nucleic acids have high potential in oligonucleotide therapeutics, chemical biology, and nanotechnology. For example, properly designed crosslinking structures provide high activity and nuclease resistance for anti-miRNAs. The noncovalent labeling and modification by the threaded structures are useful as new chemical biology tools. Photoreversible crosslinking creates smart materials, such as reversible photoresponsive gels and DNA origami objects. This review introduces the creation of interstrand crosslinking and threaded structures, such as catenanes and rotaxanes, based on hybridization-specific chemical reactions and their functions and perspectives.

Selective Photo-Crosslinking Detection of Methylated Cytosine in DNA Duplex Aided by a Cationic Comb-Type Copolymer

In the process of cell development and differentiation, C-5-methylation of cytosine (5-methylcytosine: 5-mC) in genome DNA is an important transcriptional regulator that switches between differentiated and undifferentiated states. Further, abnormal DNA methylations are often present in tumor suppressor genes and are associated with many diseases. Therefore, 5-mC detection technology is an important tool in the most exciting fields of molecular biology and diagnosing diseases such as cancers. In this study, we found a novel photo-crosslinking property of psoralen-conjugated oligonucleotide (Ps-Oligo) to the double-stranded DNA (ds-DNA) containing 5-mC in the presence of a cationic comb-type copolymer, poly(allylamine)-graft-dextran (PAA-g-Dex). Photo-crosslinking efficiency of Ps-Oligo to 5-mC in ds-DNA was markedly enhanced in the presence of PAA-g-Dex, permitting 5-mC-targeted crosslinking. We believe that the combination of PAA-g-Dex and Ps-Oligo will be an effective tool for detecting 5-mC in genomic DNA.

Rapid Alkene-Alkene Photo-Cross-Linking on the Base-Flipping-Out Field in Duplex DNA

Specific chemical reactions by enzymes acting on a nucleobase are realized by flipping the target base out of the helix. Similarly, artificial oligodeoxynucleotides (ODNs) can also induce the base flipping and a specific chemical reaction. We now report an easily prepared and unique structure-providing photo-cross-linking reaction by taking advantage of the base-flipping-out field formed by alkene-type base-flipping-inducing artificial bases. Two 3-arylethenyl-5-methyl-2-pyridone nucleosides with the Ph or An group were synthesized and incorporated into the ODNs. We found that the two Ph derivatives provided the cross-linked product in a high yield only by a 10 s photoirradiation when their alkenes overlap each other in the duplex DNA. The highly efficient reaction enabled forming a cross-linked product even when using the duplex with a low T_m value.

Photochemical modifications for DNA/RNA oligonucleotides

Light-triggered chemical reactions can provide excellent tools to investigate the fundamental mechanisms important in biology. Light is easily applicable and orthogonal to most cellular events, and its dose and locality can be controlled in tissues and cells. Light-induced conversion of photochemical groups installed on small molecules, proteins, and oligonucleotides can alter their functional states and thus the ensuing biological events. Recently, photochemical control of DNA/RNA structure and function has garnered attention thanks to the rapidly expanding photochemistry used in diverse biological applications. Photoconvertible groups can be incorporated in the backbone, ribose, and nucleobase of an oligonucleotide to undergo various irreversible and reversible light-induced reactions such as cleavage, crosslinking, isomerization, and intramolecular cyclization reactions. In this review, we gather a list of photoconvertible groups used in oligonucleotides and summarize their reaction characteristics, impacts on DNA/RNA thermal stability and structure, as well as their biological applications.

Pyrrolidinyl Peptide Nucleic Acid Probes Capable of Crosslinking with DNA: Effects of Terminal and Internal Modifications on Crosslink Efficiency

In this study, we describe a furan-modified acpcPNA as a probe that can form an interstrand crosslink (ICL) with its DNA target upon activation with N-bromosuccinimide (NBS). To overcome the problem of furan instability under acidic conditions, a simple and versatile post-synthetic methodology for the attachment of the furan group to the PNA probe was developed. Unlike in other designs, the furan was placed at the end of the PNA molecule or tethered to the PNA backbone with all the base pairs in the PNA ⋅ DNA duplexes fully preserved. Hence, the true reactivity of each nucleobase towards the crosslinking could be compared. We show that all DNA bases except T could participate in the crosslinking reaction when the furan was placed at the end of the PNA strand. The crosslinking process was sensitive to mispairing, and lower crosslinking efficiency was observed in the presence of a base-mismatch in the PNA ⋅ DNA duplex. In contrast, when the furan was placed at internal positions of the acpcPNA ⋅ DNA duplex, no ICL was observed; this was explained by the inability of a hydrogen-bonded nucleobase to participate in the crosslinking reaction. The crosslinking efficiency was considerably improved, despite lower duplex stability, when an unpaired base (in the form of C-insertion) was present in the complementary DNA strand close to the furan modification site.

Strong Inhibitory Effects of Antisense Probes on Gene Expression through Ultrafast RNA Photocrosslinking

We have reported the photochemical regulation of the intracellular antisense effect of antisense probes containing a photo-responsive artificial nucleic acid, 3-cyanovinylcarbazole nucleoside (^CNV K). Here we focus on the importance of the photocrosslinking rate on the inhibitory effect on gene expression using photocrosslinkable antisense probes (pcASOs). The inhibitory effect of pcASOs on GFP gene expression was dependent on the photocrosslinking rate of 3-cyanovinylcarbazole with d-threoninol (^CNV D), ^CNV K, or psoralen. The ultrafast RNA photocrosslinking induced the formation of a thermally irreversible covalent bond between pcASOs and the target RNA. These ASOs strongly inhibited gene expression only when the photocrosslinking rate was faster than the random walk of branch migration. In addition, pcASOs containing ^CNV D or ^CNV K targeted the RNAs with secondary structures. These results indicate the regulatory effect of photocrosslinker and photoirradiation energy using pcASOs on the gene expression level.