UMR9187 / U1196 – Chimie, modélisation et imagerie pour la biologie

Publications de l’unité

Année de publication : 2017

Donati L., Nilchian M., Trepout S., Messaoudi C., Marco S., Unser M. (2017 Aug 1)

Compressed sensing for STEM tomography

ULTRAMICROSCOPY : 179 : 47-56 : DOI : 10.1016/j.ultramic.2017.04.003 En savoir plus
Résumé

A central challenge in scanning transmission electron microscopy (STEM) is to reduce the electron radiation dosage required for accurate imaging of 3D biological nano-structures. Methods that permit tomographic reconstruction from a reduced number of STEM acquisitions without introducing significant degradation in the final volume are thus of particular importance. In random-beam STEM (RB-STEM), the projection measurements are acquired by randomly scanning a subset of pixels at every tilt view. In this work, we present a tailored RB-STEM acquisition-reconstruction framework that fully exploits the compressed sensing principles. We first demonstrate that RB-STEM acquisition fulfills the « incoherence » condition when the image is expressed in terms of wavelets. We then propose a regularized tomographic reconstruction framework to recover volumes from RB-STEM measurements. We demonstrate through simulations on synthetic and real projection measurements that the proposed framework reconstructs high-quality volumes from strongly downsampled RB-STEM data and outperforms existing techniques at doing so. This application of compressed sensing principles to STEM paves the way for a practical implementation of RB-STEM and opens new perspectives for high-quality reconstructions in STEM tomography. (C) 2017 The Authors. Published by Elsevier B.V.

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Marie-Paule Teulade-Fichou, Joël Lefebvre, Corinne Guetta, Florent Poyer, Florence Mahuteau-Betzer (2017 Jul 13)

Copper-alkyne complexation is responsible for the Nucleolar Localisation of Quadruplex Nucleic Acid Drugs Labelled by Click Chemistry.

Angewandte Chemie (International ed. in English) : Online publication : DOI : 10.1002/anie.201703783 En savoir plus
Résumé

G-quadruplex(es) (G4) are non-canonical nucleic acid structures found in guanine-rich sequences. They can be targeted with small molecules (G4-ligands) acting as reporters, for tracking both in vitro and in cells. We explored the cellular localisation of PhenDC3, one of the most powerful G4 ligands, by synthesising two clickable azide and alkyne derivatives (PhenDC3-alk, PhenDC3-az) and labelling them in situ with the corresponding Cy5 click partners. A careful comparison of the results obtained for the copper-based CuAAC and copper-free SPAAC methodologies in fixed cells implicated Cu(I) /alkyne intermediates in the non-specific localisation of ligands (and fluorophores) to the nucleoli. By contrast, SPAAC yielded similar nucleoplasmic labelling patterns in fixed and live cells. Our findings demonstrate the need for great care when using CuAAC to localise drugs in cells, and show that SPAAC gives results that are more consistent between fixed and live cells.

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María José Lista, Rodrigo Prado Martins, Olivier Billant, Marie-Astrid Contesse, Sarah Findakly, Pierre Pochard, Chrysoula Daskalogianni, Claire Beauvineau, Corinne Guetta, Christophe Jamin, Marie-Paule Teulade-Fichou, Robin Fåhraeus, Cécile Voisset, Marc Blondel (2017 Jul 8)

Nucleolin directly mediates Epstein-Barr virus immune evasion through binding to G-quadruplexes of EBNA1 mRNA.

Nature communications : 16043 : DOI : 10.1038/ncomms16043 En savoir plus
Résumé

The oncogenic Epstein-Barr virus (EBV) evades the immune system but has an Achilles heel: its genome maintenance protein EBNA1, which is essential for viral genome maintenance but highly antigenic. EBV has seemingly evolved a system in which the mRNA sequence encoding the glycine-alanine repeats (GAr) of the EBNA1 protein limits its expression to the minimal level necessary for function while minimizing immune recognition. Here, we identify nucleolin (NCL) as a host factor required for this process via a direct interaction with G-quadruplexes formed in GAr-encoding mRNA sequence. Overexpression of NCL enhances GAr-based inhibition of EBNA1 protein expression, whereas its downregulation relieves the suppression of both expression and antigen presentation. Moreover, the G-quadruplex ligand PhenDC3 prevents NCL binding to EBNA1 mRNA and reverses GAr-mediated repression of EBNA1 expression and antigen presentation. Hence the NCL-EBNA1 mRNA interaction is a relevant therapeutic target to trigger an immune response against EBV-carrying cancers.

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Chennoufi R., Mahuteau-Betzer F., Tauc P., Teulade-Fichou M.P., Deprez E. (2017 Jun 18)

Triphenylamines Induce Cell Death Upon 2-Photon Excitation

MOLECULAR IMAGING : 16 : DOI : 10.1177/1536012117714164 En savoir plus
Résumé

Photodynamic therapy (PDT) is a promising therapeutic method for several diseases, in particular for cancer. This approach uses a photosensitizer, oxygen, and an external light source to produce reactive oxygen species (ROS) at lethal doses to induce cell death. One drawback of current PDT is the use of visible light which has poor penetration in tissues. Such a limitation could be overcome by the use of novel organic compounds compatible with photoactivation under near-infrared light excitation. Triphenylamines (TPAs) are highly fluorescent compounds that are efficient to induce cell death upon visible light excitation (458 nm), but outside the biological spectral window. Interestingly, we recently showed that TPAs target cytoplasmic organelles of living cells, mainly mitochondria, and induce a high ROS production upon 2-photon excitation (in the 760-860 nm range), leading to a fast apoptosis process. However, we observed significant differences among the tested TPA compounds in terms of cell distribution and time courses of cell death-related events (apoptosis vs necrosis). In summary, TPAs represent serious candidates as photosensitizers that are compatible with 2-photon excitation to simultaneously trigger and imaging cell death although the relationship between their subcellular localization and the cell death mechanism involved is still a matter of debate.

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