Optochemical Control of Cell Contractility in Drosophila Embryos

Synchronization in epithelial tissue morphogenesis

Coordination of cell behavior is central to morphogenesis, when arrays of cells simultaneously undergo shape changes or dynamic rearrangements. In epithelia, cell shape changes invariably exert mechanical forces, which adjacent cells could sense to trigger an active response. However, molecular mechanisms for such mechano-transduction and especially their role for tissue-wide coordination in morphogenesis have remained ambiguous. Here, we investigate the function of Tmc, a key component of cellular mechano-transduction in vertebrate hearing, for coordination of cell dynamics in the epithelial amnioserosa of Drosophila embryos. We directly probed cell-cell mechano-transduction in vivo by opto-chemically inducing single-cell contractions and discovered a Tmc-dependent contraction response in neighboring cell groups. On the tissue scale, we uncover synchronization of neighboring cell area oscillations, which is impaired in Tmc mutants. A data-driven model of Tmc-dependent cell-cell interactions predicts that synchronization leads to an isotropic force map and effectively shields the tissue from external mechanical pulling. By microdissection, we detect equal junction tension along the axial and lateral axis in wild-type but increased lateral tension in Tmc mutants. Thus, Tmc transduces forces into an intracellular response that coordinates mechanical cell behavior in epithelial tissue.

Dynamics and functions of E-cadherin complexes in epithelial cell and tissue morphogenesis

Cell-cell adhesion is at the center of structure and dynamics of epithelial tissue. E-cadherin-catenin complexes mediate Ca2+-dependent trans-homodimerization and constitute the kernel of adherens junctions. Beyond the basic function of cell-cell adhesion, recent progress sheds light the dynamics and interwind interactions of individual E-cadherin-catenin complex with E-cadherin superclusters, contractile actomyosin and mechanics of the cortex and adhesion. The nanoscale architecture of E-cadherin complexes together with cis-interactions and interactions with cortical actomyosin adjust to junctional tension and mechano-transduction by reinforcement or weakening of specific features of the interactions. Although post-translational modifications such as phosphorylation and glycosylation have been implicated, their role for specific aspects of in E-cadherin function has remained unclear. Here, we provide an overview of the E-cadherin complex in epithelial cell and tissue morphogenesis focusing on nanoscale architectures by super-resolution approaches and post-translational modifications from recent, in particular in vivo, studies. Furthermore, we review the computational modelling in E-cadherin complexes and highlight how computational modelling has contributed to a deeper understanding of the E-cadherin complexes.