From the Yeast cell wall to new strategies in the fight against Ciguatera

Séminaire Scientifique au Centre de Recherches Insulaires et Observatoire de l’Environnement (CRIOBE, USR 3278)I will attempt to explain my scientific journey, from studying the cell wall and stress responsemechanisms of yeasts, up to the development of innovative approaches to fight Ciguatera, a majorcause of food poisonings by seafood worldwide.Yeasts are eukaryotic microorganisms traditionally used by man to make bread, beer and wineand thus very well studied. Their cells are surrounded by a thick cell wall composed of glycans andproteins organized in a complex multilayered architecture. Essential for the survival of yeasts andfungi, this highly dynamic organelle gets constantly remodeled during the cell cycle to allowmorphogenetic events as well as upon environmental changes. It is a key player in cellular adhesionand resistance to antifungal compounds. While studying the mechanisms of cell wall adaptations tovarious stresses, I came across the different cellular signaling pathways involved notably MAP kinasecascades and the Calcineurin pathway which are conserved with higher eukaryotes.Ciguatoxins (CTXs) are lipid-soluble, highly neurotoxic, polyether compounds produced bydinoflagellates from the genus Gambierdiscus spp.. mostly found in tropical and subtropical zones.CTXs bind to Voltage Gated Sodium Channels at the surface of human sensory neurons where theyremain, causing Ciguatera Fish Poisoning or CFP. This severe disease is characterized by with avariety of gastrointestinal, cardiovascular and neurological symptoms (paresthesia, ataxia, coldallodynia), including persistent neurological effects. Despite the importance and prevalence of CFP,there is so far no simple and quick way of detecting these toxins in contaminated samples. Currently,only heavy and expensive laboratory methods are available to detect them: LC-MS/MS, receptorbinding assays by competition with labeled compounds, and neuroblastoma cell-based assaysperformed on mammalian neurons. We have started to engineer biosensors based on the detection ofa transcriptional signal in the model yeast Saccharomyces cerevisiae, using the very goodconservation of its signaling pathways with higher eukaryotes.Finally, I will also present a smaller project (NeuroSens) based on a different strategy, to studyand characterize the binding of Ciguatoxins on mammalian neuronal cells by Single Molecule ForceSpectroscopy using Atomic Force Microscopy