Role of mechanosensitive ion channels in coordinated epithelial cell dynamics in Drosophila

Abstract

Epithelial cells are able to sense and mechanically respond to the forces and movements generated and transmitted through their neighbors. These forces are multicellular at the tissue level, and are transmitted via multimeric protein complexes at the cell adhesion sites between two neighboring cells. The cell membrane in epithelial cells serve as a major site for receiving external mechanical forces, and via mechano-transduction these stimuli are converted into intracellular biochemical signals. Previous understanding of the junctional adhesion complexes (cadherin/catenin complex) may provide an insight, yet the key molecular components of mechano-transduction remained unidentified so far. In this study, we hypothesize that mechanosensitive (MS) ion channels (TMC, NOMPC and Piezo), might respond to the changes in tension at the plasma membrane and are crucial for maintenance and establishment coordinated cell behavior. A major morphogenetic transformation event in Drosophila embryos is Dorsal closure (DC). This event critically depends on the dynamics of a squamous epithelium called the Amnioserosa (AS). AS cells exhibit dynamic mechanical behavior that appears to be coordinated between cells by undergoing stable oscillations between cross-sectional area. In addition, AS cells are highly accessible to genetic manipulations and quantitative live cell imaging. This provides a robust model system to study mechanosensing and mechano-transduction in epithelial cells. Changes in tension at the adherens junction could be detected via mechano-transduction pathways, allowing cells to communicate with each other. I have found that MS ion channels are expressed in AS epithelium and are involved in establishing coordination between AS cells. In particular, I have found that the putative ion channel TMC is required for achieving isotropic junction tension and morphology within the AS. In order to understand the potential role of MS ion channels in establishing this coordinated cell behavior, I established methods and assays to follow Ca2+ dynamics and turnover in the AS cells. This study could reveal and characterize previously unanticipated functions of MS putative ion channel TMC in epithelial tissue morphogenesis. I attempted to elucidate the principles by which the interaction of adherens junctions and MS ion channels may contribute to guide the active mechanical behavior in the epithelial cells.