Proposer/Coanimator Camilla Luccardini Véronique Morel Abstract: Light microscopy is very helpful to give information on protein localization at the cellular scale, but investigation of protein interactions at the subcellular, nanometric scale is prevented by the diffraction limit. To decipher sub-cellular ultra-structure biologists have long used electron microscopy (EM), which has a higher resolving power (up to 10-10m) since it uses an electron beam to illuminate the sample. However, EM is still limited in the choice of antibodies as protein reporters. This dead end has been solved with the development of expansion microscopy, a break through technique of sample preparation allowing to increase sample size by at least 4x and push the resolution limits of microscopes. We developed a high-resolution microscopy approach by combining expansion with STED microscopy. This strategy allows us to separate a highly dense molecular complex such as the centriole and its associated proteins. The aim of this workshop is to share our “savoir faire” with the audience. We will discuss how to perform expansion on cultured cells and Drosophila ciliated tissues, giving you all the tips and tricks that you need when you are a beginner. We will talk about the benefits and the limits of this technique and will compare confocal vs STED imaging on expanded samples.