Biosciences Research Seminar - Morphogenesis during cnidarian gastrulation

In cnidarians, embryogenesis produces ciliated larvae called a planula, which has a very simple body plan: typically, cylindrical and roughly torpedo -shaped with a principal polarized “oral-aboral” axis and two epithelia body layers. These common planula features are established during gastrulation, but the morphogenesis processes involved vary markedly between different cnidarian species. In the hydrozoan laboratory model Clytia hemisphaerica, gastrulation involves a process termed unipolar cell ingression, in which the inner epithelium (endoderm) derives from mass epithelial-mesenchymal transition at the future oral pole of a monoepithelial blastula. This contrasts markedly from the gastrulation mode in the anthozoan Nematostella vectensis, in which endoderm formation primarily relies on cell sheet invagination. Observations of cell morphology and modelling approaches have helped to build a more complete understanding of the cellular basis of gastrulation in Clytia, and though comparisons with Nematostella and other species provide insights into the evolutionary plasticity of cnidarian gastrulation modes.