L'assemblage d'une machinerie mécanosensible des jonctions adhérentes déclenche la polymérisation et le remodelage de l'actine en réponse à la force actomyosine
Year: 2025
Type: dissertation
Abstract: Cells establish connections with each other (cell-cell adhesions) and with their environment (cell-ECM adhesions) to maintain the integrity of healthy tissues and regulate numerous biological processes, including morphogenesis, collective cell migration, and wound healing. These structures enable tissues to maintain their tensegrity by sensing and adapting to intracellular and extracellular mechanical cues, which are converted into biochemical signals through a process called mechanotransduction. This requires the establishment and maintenance of mechanosensitive cell-cell junctions. First, cells initiate contact with each other by projecting lamellipodia, which rely on actin branching by Arp2/3. This process enables the formation of cadherin-based adherens junctions (AJs). As these AJs mature, a remodelling of the branched actin network into contractile networks, associated with the recruitment and regulation of mechanosensitive proteins such as α-catenin, vinculin and VASP, results in adhesion strengthening. In cells, studies suggest that these proteins are recruited in an actomyosin-dependent manner at AJs where they regulate actin polymerisation and organisation. However, the mechanisms by which actomyosin activity drives the assembly of AJ components to modulate actin dynamics and architecture remain unclear. The aim of this project was therefore to study the molecular mechanisms by which AJ proteins assemble in response to actomyosin contraction and regulate actin polymerisation and organisation. The complex signalling environment that controls AJs justifies disentangling these pathways by isolating this machinery in an in vitro assay made of purified proteins. To achieve this, we have developed a minimal system whose spatial organisation mimics the 2D architecture of the apical side of epithelial tissue. This artificial structure is a micropatterned honeycomb network in which the edges of the ‘artificial cells’ are decorated with α-catenin. This experimental system, in which the concentration and spatial organisation of a set of known components are adjustable, enables the observation of the recruitment of fluorescent proteins and their ability to regulate actin polymerisation and organisation using TIRF microscopy. We have successfully reconstituted AJ mechanosensitivity in vitro using up to eight proteins. Our observations show that binding a contractile actomyosin network to α-catenin is sufficient to induce assembly of α-catenin, vinculin, and VASP. Once formed, this machinery promotes actin assembly, inhibits the formation of Arp2/3-mediated branched actin networks, and remodels the actin cytoskeleton into thick bundles.
Source: theses.fr (ABES)
Author: Favarin, Aurélie
Language: English
Subfield: Cell Biology
Domain: Life Sciences
Open Access status: green
OpenAlex ID: W7112515652
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