The yeast Saccharomyces cerevisiae cell wall: Molecular architecture, regulatory pathways and remodelling mechanisms in response to environmental conditions, and biotechnological values

207 ref. *INRA UMR 792 Biotechnologies Bioprocédés 31077 Toulouse (FRA) Diffusion du document : INRA UMR 792 Biotechnologies Bioprocédés 31077 Toulouse (FRA)International audienc

KNR4 is a member of the PKC1 signalling pathway and genetically interacts with BCK2, a gene involved in cell progression in Saccharomyces cerevisiae

38 ref.International audienc

The interaction of Slt2 MAP kinase with Knr4 is necessary for signalling through the cell wall integrity pathway in Saccharomyces cerevisiae

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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

Saccharomyces cerevisiae YCRO 17c/CWH43 encodes a putative sensor/transporter protein upstream of the BCK2 branch of the PKC1-dependent cell wall integrity pathway

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Putative Stress Sensors WscA and WscB Are Involved in Hypo-Osmotic and Acidic pH Stress Tolerance in Aspergillus nidulans ▿ †

Wsc proteins have been identified in fungi and are believed to be stress sensors in the cell wall integrity (CWI) signaling pathway. In this study, we characterized the sensor orthologs WscA and WscB in Aspergillus nidulans. Using hemagglutinin-tagged WscA and WscB, we showed both Wsc proteins to be N- and O-glycosylated and localized in the cell wall and membrane, implying that they are potential cell surface sensors. The wscA disruptant (ΔwscA) strain was characterized by reduced colony and conidia formation and a high frequency of swollen hyphae under hypo-osmotic conditions. The deficient phenotype of the ΔwscA strain was facilitated by acidification, but not by alkalization or antifungal agents. In contrast, osmotic stabilization restored the normal phenotype in the ΔwscA strain. A similar inhibition was observed in the wscB disruptant strain, but to a lesser extent. In addition, a double wscA and wscB disruptant (ΔwscA ΔwscB) strain was viable, but its growth was inhibited to a greater degree, indicating that the functions of the products of these genes are redundant. Transcription of α-1,3-glucan synthase genes (agsA and agsB) was significantly altered in the wscA disruptant strain, resulting in an increase in the amount of alkali-soluble cell wall glucan compared to that in the wild-type (wt) strain. An increase in mitogen-activated protein kinase (MpkA) phosphorylation was observed as a result of wsc disruption. Moreover, the transient transcriptional upregulation of the agsB gene via MpkA signaling was observed in the ΔwscA ΔwscB strain to the same degree as in the wt strain. These results indicate that A. nidulans Wsc proteins have a different sensing spectrum and downstream signaling pathway than those in the yeast Saccharomyces cerevisiae and that they play an important role in CWI under hypo-osmotic and acidic pH conditions