Meeting Abstract
Epithelial tissues typically act as barriers and provide support to organs and embryos, but during development, these tissues also display a dynamic, fluid-like behavior. During morphogenesis, epithelial tissues undergo both elastic (reversible) and plastic (irreversible) shape changes often characterized by local cell rearrangement mechanisms such as intercalation and rosette formation, which are primarily orchestrated by genetic programs (e.g. drosophila). Here, we have discovered a novel fracture-based mechanism by which epithelial tissues can exhibit fast and extreme plastic shape changes in a simple, flat, early divergent animal – Trichoplax adhaerens. These animals continuously glide on substrates using ciliary traction to generate mechanical forces – which lead to real-time organismal shape changes and also induce local stresses in the tissue. The epithelium is surprisingly able to sustain local physiological fracture holes (~min), which can either enlarge or ‘heal’ (~hr), resulting in permanent plastic shape change and topological cell rearrangement, with similarities to actomyosin purse-string healing. We employ live microscopy, novel bead-based tagging and engineering mechanics analysis to quantitatively demonstrate how forces mainly govern tissue fractures. We also use agent-based active elastic sheet models & simulations to uncover how ‘soft zones’ in tissues are created to enable morphological solid-to-liquid tissue transitions. We reveal how tissue fractures and healing play a critical role in the entire life cycle of these animals – during their (i) continuous shape change, and (ii) asexual reproduction, where an individual animal ‘splits into two’ by binary fission.
