Tissue Fracture Dynamics governs Mechanics of Morphogenesis in a Simple, Early Divergent Metazoan

Tissue flow mechanics dictate shape and form in all animals, and is commonly regulated by genetics. Here, we have discovered a novel case of morphogenesis regulated by tissue fracture dynamics in a simple, early divergent animal - the Trichoplax adhaerens. Live microscopy reveals that adult animals are capable of real-time extreme shape changes exhibiting both solid-like and liquid-like tissue properties. We quantitatively studied this phenomenon by developing a novel technique for long duration (~hrs) and large-scale (~mm) morphogenetic imaging and tracking of thousands of cells. We find surprising fluid-like patterns including vortices and shear zones. The ventral epithelial cells can physiologically undergo fast (~sec) and local cell rearrangements in response to internally generated forces. We find that these cellular rearrangements reflect mechanical force patterns generated by the animal’s natural movements. We further observe local micro-fracture dynamics that lead to tissue rearrangements. Remarkably, these fractures can heal over time and lead to permanent shape change. We demonstrate that micro-scale fracture and healing dynamics govern two biologically important phenomena – asexual reproduction by fission, and tissue mixing in an early divergent metazoan.