Cellular Detection of G‐Quadruplexes by Optical Imaging Methods

G-quadruplexes (G4s) are higher-order nucleic acid structures that fold from guanine (G)–rich DNA and RNA strands. This field of research gains traction as a major chemical biology area since it aims at uncovering many key cellular mechanisms in which quadruplexes are involved. The wealth of knowledge acquired over the past three decades strongly supports pivotal roles of G4 in the regulation of gene expression at both transcriptional (DNA quadruplexes) and translational levels (RNA quadruplexes). Recent biochemical discoveries uncovered myriad of additional G4 actions: from chromosomal stability to the firing of replication origins, from telomere homeostasis to functional dysregulations underlying genetic diseases (including cancers and neurodegeneration). Here, we listed a repertoire of protocols that we have developed over the past years to visualize quadruplexes in cells. These achievements were made possible thanks to the discovery of a novel family of versatile quadruplex-selective fluorophores, the twice-as-smart quadruplex ligands named TASQ (for template-assembled synthetic G-quartet). The versatility of this probe allows for multiple imaging techniques in both fixed and live cells, including the use of the multiphoton microscopy, confocal microscopy, and real-time fluorescent image collection. © 2017 by John Wiley & Sons, Inc. Keywords: G-quadruplex; fluorescence; smart probes; microscopy; live cell imaging