Mechanical Anisotropy in E-cadherin-Induced Polarized Actin Architecture as a Driver of Interfacial Opening and Adherens Junction Formation Between Cells - Project Summary/Abstract Cadherin mediated cell-cell contact formation is essential for tissue integrity and organization. It has been proposed that the dynamic reorganization of cadherins and the actomyosin cortex is critical for the opening of cell-cell contacts. Although disruptions in adherens junctional complex can lead to diseases such as tumor metastasis and developmental disorders, the mechanisms by which cadherins regulate the mechanical properties of the actomyosin cortex are not fully understood. Active gel theory suggests that uneven mechanical stress within the actomyosin network drives flow, which facilitates the opening of intercellular junctions by depleting the F-actin and reducing interfacial tension. E-cadherin clusters are thought to modulate mechanical stress within the cortex through two primary pathways: (1) local inhibition of myosin contractility via depletion of Rho GTPases, and (2) direct mechanical coupling with actin. The current model primarily focuses on the first pathway, where E-cadherin-mediated downregulation of RhoA-GTP inhibits myosin-II activity at the contact center, initiating centrifugal F-actin flows. However, this model does not fully explain how E-cadherin clusters and actin co-localize at the contact rim once a steady state is reached. Therefore, we aim to investigate how the alternative pathway, involving direct interaction between E-cadherin and actin, modulates actomyosin symmetry breaking and leads to the dynamic reorganization of the cortical actomyosin network. Previous studies have identified key mechanical properties of the adherens junctional complex and the actomyosin network, showing that junctional adaptor proteins such as α-catenin and vinculin form directionally asymmetric catch bonds with F-actin. These asymmetric interactions suggest that E-cadherin clusters may promote the formation of anisotropic F-actin polar asters, with (+)-barbed ends oriented toward the center. Since myosin motors generate contractile forces between antiparallel actin filaments, the arms of these asters can be stabilized by catch bonds when they coupled to the opposite arm of another aster. Therefore, I propose that chain of E-cadherin clusters, linked by arms from actin asters, form the basic architecture of the interfacial actomyosin network. This ring- shaped structure can then expand due to the outward mechanical stress superimposed by local anisotropy and concentration gradients within the actomyosin network. In this proposal, I will test the following hypotheses to explore this working model. First, I will examine the mechanical coupling between E-cadherin clusters in close proximity using a patterned supported lipid bilayer model. Next, I will Investigate the arrangement-dependent mechanical coupling between E-cadherin clusters by addressing quantification of attractive force and position- dependent lifetime of E-cadherin clusters. Finally, I will develop a biophysical model, grounded on active polar gel model, to understand the role of mechanical coupling in interface opening. By addressing these hypotheses, this research will enhance our understanding of how E-cadherin clusters and actomyosin networks interact to regulate the formation of cell-cell contacts.
