Versatile Click Chemistry-based Approaches to Illuminate DNA and RNA G-Quadruplexes in Human Cells

The existence and functional relevance of DNA and RNA G-quadruplexes (G4s) in human cells is now beyond debate, but how did we reach such a level of confidence? Thanks to a panoply of molecular tools and techniques that are now routinely implemented in wet labs. Among them, G4 imaging ranks high because of its reliability and practical convenience, which now makes cellular G4 detection quick and easy; also, because this technique is sensitive and responsive to any G4 modulations in cells, which thus allows gaining precious insights into G4 biology. Herein, we briefly explain what a G4 is and how they can be visualized in human cells; then, we present the strategy we have been developing for several years now for in situ click G4 imaging, which relies on the use of biomimetic G4 ligands referred to as TASQs (for template-assembled synthetic G-quartets) and is far more straightforward and modular than classically used immunodetection methods. We thus show why and how to illuminate G4s with TASQs and provide a detailed, step-by-step methodology (including the preparation of the materials, the methodology per se, and a series of notes to address any possible pitfalls that may arise during the experiments) to make G4 imaging ever easier to operate. Key features • MultiTASQs are clickable probes usable for the detection of cellular DNA and RNA G-quadruplex (G4). • In situ click chemistry relies on the labeling of G4 by clickable probes once in their cellular binding sites. • Experiments can be performed by incubating the clickable probe either in live cells or in fixed cells. • The published but unoptimized protocol is now totally revised to allow for reliable G4 detection in human cells.