Visualization of DNA and RNA quadruplex formation in human cells was demonstrated recently with different quadruplex-specific antibodies. Despite the significant interest in these immunodetection approaches, dynamic detection of quadruplex in live cells remains elusive. Here, we report on NaphthoTASQ (N-TASQ), a next-generation quadruplex ligand that acts as a multiphoton turn-on fluorescent probe. Single-step incubation of human and mouse cells with N-TASQ enables the direct detection of RNA-quadruplexes in untreated cells (no fixation, permeabilization or mounting steps), thus offering a unique, unbiased visualization of quadruplexes in live cells.

International audienceComposite films based on chitosan and lignin biopolymers were investigated for their mechanical, barrier, surface, and antioxidant properties and linked to an extensive microscopic analysis of their external and internal structure. In particular, the fluorescence properties of lignins were exploited, using two-photon microscopy, to achieve a 3D representation of its distribution within the chitosan matrix. The lignin incorporation generated small aggregates homogeneously distributed in the film. The aggregates slightly weakened the network as reflected by the mechanical properties. Lignin as an antioxidant provided to the film a radical scavenging activity, essentially governed by a surface activity mechanism. Accordingly, the film surface showed a chemical reorganization induced by the presence of lignin as highlighted by surface hydrophobicity and X-ray photoelectron spectroscopy. On the molecular scale, solid state NMR also revealed the absence of covalent bonds between lignin and chitosan and the establishment, but to a small extent, of low energy dipole dipole interactions. Finally, lignin is a promising compound for a good added-value due to radical scavenging in a chitosan matrix

Molecular interactions are key to many chemical and biological processes like protein function. In many signaling processes they occur in sub-cellular areas displaying nanoscale organizations and involving molecular assemblies. The nanometric dimensions and the dynamic nature of the interactions make their investigations complex in live cells. While super-resolution fluorescence microscopies offer live-cell molecular imaging with sub-wavelength resolutions, they lack specificity for distinguishing interacting molecule populations. Here we combine super-resolution microscopy and single-molecule Förster Resonance Energy Transfer (FRET) to identify dimers of receptors induced by ligand binding and provide super-resolved images of their membrane distribution in live cells. By developing a two-color universal-Point-Accumulation-In-the-Nanoscale-Topography (uPAINT) method, dimers of epidermal growth factor receptors (EGFR) activated by EGF are studied at ultra-high densities, revealing preferential cell-edge sub-localization. This methodology which is specifically devoted to the study of molecules in interaction, may find other applications in biological systems where understanding of molecular organization is crucial.