Mechanisms of Cell Wall Mechanosensation for the Regulation of Cell Growth – CellWallSense

The project focuses on the study of the cell wall in fungi, and in particular the mechanisms of mechanosensation. It uses methods including microscopy, genetics and modeling

By studying the dynamic localization of the Cell Wall sensor Wsc1p in fission yeast; we uncovered that it can form large clusters at sites where the Cell Wall is mechanically pressed. This occurs at sites of cell-cell contact in interphase or during mating, and can be exacerbated by growing cells in confined environment in microfabricated channels. By mapping Cell Wall deformation together with Wsc1 recruitment, and by manipulating Cell Wall stress, we established that this local recruitment occurs in dose-dependence with Cell Wall mechanical stress. These data suggested that Wsc1 is a bona fide Cell Wall mechanosensor.

We screened for mutants in membrane trafficking, polarity or the cytoskeleton, and found that mechanosensing by Wsc1 is independent of these canonical effectors. By generating truncation alleles, we showed, that force detection and clustering depend on the large extracellular domains that interact with Cell Wall carbohydrate. FRAP analysis, further suggested that this protein diffuses laterally at the cell surface, and that diffusivity may be reduced at sites where
the cell wall is compressed. From these data we proposed a “kinetic-trap” model in which mechanodetection at sites of Cell Wall compression may be mediated by an enhanced engagement of sensors with the Cell Wall, that restrict diffusivity and allow the formation of sensosomes to repair the Cell Wall . These data were published in one important recent paper (Neeli-Venkata et al. Developmental Cell, 2021).

As follow-up projects, we now would like to understand how molecular mechanosensors architecture may have evolved to support CW integrity among different types of CWs and cell growth properties found in fungi. Notably, Wsc1 is found across all fungi, and has similar extracellular domains (a STR long “nano-spring” domain, and a smaller CW-binding WSC domain). Yet, the STR domain exhibits interesting variations in length suggesting that different sensors could have built-in properties to promote CW mechanosensation in different species. To address this, we are pursuing two different lines of investigation: (i) We are developing super-resolution methods to map sensor size directly in vivo, by tagging the C and N-ter with different fluorophores; and (ii) we express several Wsc homologues from different species in fission yeast, and use our set of quantitative tools for CW analysis, to test if and how they detect and transduce forces on the CW with more or less sensitivity. Finally, we are alos studying more broadly the function of mechanosensing in the Cell Wall in different polar growth transitions such as during mating, New end take off, branching or germination.

Published Papers and Reviews:
1- Chevalier L, Pinar Sala M, Le Borgne R , Durieu C, Peñalva M, Boudaoud A# and Minc N# (2022) Cell Wall Dynamics in a Filamentous Fungus. BioRxiv. doi: 10.1101/2022.06.12. 495826.
2- Municio-Diaz C, Muller E, Drevensek S, Fruleux A, Lorenzetti Z, Boudaoud A# and Minc N# (2022) «Mechanobiology of the cell wall – insights from tip-growing plant and fungal cells« , J Cell Science, 135 (21): jcs259208.
3- Neeli-Venkata R, Municio Diaz C, Celador R, Sanchez Y, Minc N (2021) «Detection of surface forces by the cell-wall mechanosensor Wsc1 in yeast« , Developmental Cell 56, 1–15
4- Mishra R, Minc N, Peter M (2022) Cells under pressure: how yeast cells respond to mechanical forces. Trends Microbiol. 30(5). doi: 10.1016/j.tim.2021.11.006.
5- Taheraly S, Ershov D, Dmitrieff S and Minc N (2020) «An image analysis method to survey the dynamics of polar protein abundance in the regulation of tip growth«, J Cell Science, 133(22)

Papers in preparation:
1. Chevalier, L, Klingelschmitt, F, Mousseron L, Boudaoud A, and Minc N, “Mechanical Strategies Supporting Rapid Tip Growth in Filamentous Fungi” In preparation
2. Lorenzetti E, Boudaoud A, and A Fruleux, “Inference of ” In preparation

The Cell Wall (CW) is a thin and stiff layer encasing and protecting bacterial, plant and fungal cells. It undergoes dynamic modifications in mechanics and composition that drive growth, reproduction, and infection. Such modifications entail risks of CW breakage and lysis of cells, due to their high internal pressure. In fungi, those risks are mitigated by the cell wall integrity pathway (CWI), which detects CW defects through membrane mechanosensors, and promotes compensatory responses. Building on novel quantitative approaches of our consortium to dynamically map CW mechanics around live fission yeast cells, and to model walled cells growth and morphogenesis, we propose an interdisciplinary program aiming at dissecting the mechanisms of CW mechanosensing by surface sensors of the CWI and at addressing the function of mechanosensation in cell growth. This project shall shed light on the mechanisms of surface mechanosensing and their role in promoting cell survival during growth.