Meeting Abstract
Animals in their adulthood are often associated with a fixed shape and form, primarily determined by epithelial tissues, which hold organs and organ systems together. Here, we study morphogenesis in a simple, early diverging metazoan – the Trichoplax adhaerens (phylum Placozoa), known to exhibit a surprising amorphous ‘amoeboid’ shape change all throughout its adult form. The Trichoplax is one of the simplest known multicellular animals – with just six cell types and a flat, pancake-shaped three-layered body plan consisting of dorsal and ventral epithelial layers. Live microscopy reveals that adult animals are capable of real-time extreme shape changes and exhibit both a solid-like and liquid-like tissue behavior. In order to study this phenomenon, we developed a novel technique for large-scale cellular tracking over wide fields of view and long durations. We quantitatively link organism-scale shape changes to internal epithelial cell rearrangements by mapping their large-scale morphogenetic flow fields using micro-bead tags and cell tracking. We discovered that mechanical forces generated in these animals could result in physiological, localized, ventral epithelial fractures, which may either heal over time or enlarge in size, leading to large-scale cellular rearrangements and extreme shape changes such as long narrow threads. Under sufficient pulling forces, these threads may rupture, culminating the asexual reproduction process resulting in two or more daughter animals. We quantify these tissue fractures and other non-canonical tissue flow patterns, and demonstrate multi-scale tissue mixing over short and long time-scales.
