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Seeing is Believing-2,

Super-Resolution Meets Superbugs
Philippe Sansonetti
p. 41

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Source: La lettre, no. 34, July 2012

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1The morning session – A Vision of Cell Infection at Super-Resolution – illustrated the extraordinary progress made in the super-resolution of cellular imaging.

2With regard to resolution, the “optical barrier” sits at 200 nm. There is therefore a gap between the maximum level of resolution imposed by the fundamental laws of optics and that of electron microscopy which is of the order of a nanometre, that is, of the resolution of a molecule. It is however crucial that we fill this gap, as the incursion of photon microscopy into this area would contribute to its versatility: multi-colour probes, 3D observation, ability to capture the dynamics of molecular interactions (FRET), and possibility of following events live. All of these are properties that are crucial for the detailed analysis of molecular interactions governing the development of infectious processes. A number of new optical tools, possibly combined with mathe­matical image processing (STED, PALM), are now regularly bringing resolution to about 10 nm. This represents a huge step for what is now called “super-resolution”. This evolution was illustrated in the keynote lecture by Antoine Triller (ISBEN, ENS, Paris), whose study of the positioning dynamics of postsynaptic receptors as their ligands bond has led to signi­ficant advances, including through the use of new chromophores such as “quantum dots”. A real chemistry of in cellulo ima­ging is in the making. Several presentations completed these approaches: atomic force microscopy allows for the interactions between bacteria/toxins and cells to be captured in real time, thanks to the versatility of use of the “cantilever” on which its functioning is based. Its combination with the PALM method offers a previously unimaginable super-resolution, from the dynamics of cellular components to the quasi-molecular scale. Finally, as “light sheet based fluorescence” combines the classi­cal approaches of optical sections (confocal or two-photon microscopy) with optical tomography, the lateral and not vertical excitation of fluorophore, it sheds light on the focal plane. This method offers a direct use of 3D object imaging. The analysis of the evolution of organoids was presented, illustrating the quality of these approaches for studying, for example, the development and differentiation of an organized population of cells like an epithelium. Other more applied approaches showed how optical imaging that is “super-resolutive” or tends towards “super-resolution” effectively deciphers the properties of pathogenic microbes and parasites, as well as their mode of interaction with cells and tissues. This was the case of research on the dynamics of the Trypanosome parasite’s flagellum, a real molecular “conveyor belt” allowing for the assembly and homeostasis of this flagellum; of research on the dynamics of disassembly of the HIV virus at the nuclear pore that could only be shown through a “super-resolutive” approach; and of the dissection of the mode of progression of the early form of the malaria parasite: the sporozoite.

3The afternoon session – A Vision of Tissue Infection at Super-Resolution – considered the term “super-resolution” in the much broader context of improvements to the imaging of pathological processes within tissues like infection, cancer, fibrosis, ranging from improvements to the resolution of the optical analysis of the cell within the tissues, to the analysis of its molecular content through mass spectrometry. The session was introduced with a keynote lecture by Vasilis Ntziachristos (Technishe Universität and Helmholtz Centre, Munich), who showed how powerful the combination of fluorescence and opto-acoustics is, both for fundamental approaches and for medical imaging. Mass spectrometry allows for a real mapping of the presence of peptides or lipids on a tissue section or on the surface of an object to study. In terms of the molecular identification of the compounds present, the “super-resolution” afforded by mass spectrometry spectacularly complements the array of imaging techniques available. This session ended with a demonstration of the power of the two-photon microscopy approach in the dissection of micro-organisms’ pathways of progression within tissues and their effect on the epithelial and immune cells.

• Guy Tran Van Nhieu (Collège de France) and Régis Tournebize (Institut Pasteur) actively participated in defining the objectives of this symposium and choosing the speakers.

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Référence électronique

Philippe Sansonetti, « Seeing is Believing-2,  », La lettre du Collège de France [En ligne], 7 | 2015, mis en ligne le 02 novembre 2015, consulté le 23 mai 2017. URL : http://lettre-cdf.revues.org/2687

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Auteur

Philippe Sansonetti

Microbiology and Infectious Diseases

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