Epithelia are the most common tissues in animals and play a variety of functions: body shape definition and containment, protection against chemical, physical and biological aggressions, environmental sensing, secretion, and nutrient absorption. Within the IBDM, several teams study various aspect of the development and physiology of epithelia, using a wide panel of model organisms (DrosophilaXenopusC. elegans, mouse, organoids, cell lines…).

A strange newcomer is now joining this model organism zoo, the Placozoan Trichoplax adhaerens. Trichoplax is a small, flat marine animal of great anatomical and histological simplicity. It is composed almost exclusively of ciliated epithelial cells, organised in two epithelial sheets delimiting an internal cavity, and lacks any recognisable organ and major body axes. Despite its apparent simplicity, Trichoplax presents some surprising features that make it unique among all animals: in particular, it is characterised by an extreme morphological plasticity, which allows it to completely change its shape in a few minutes’ time, and by its ability to efficiently and quickly repair large mechanical wounds. The cellular and molecular bases of these phenomena remain completely unexplored, although they are probably related to the lack of basal lamina and to the absence of any intercellular junctions other than very small adherens-like junctions.

Andrea Pasini, in the Le Bivic’s team, has recently been awarded a grant from the CNRS Programme ‘Diversity of Biological Mechanisms’, to study the epithelial plasticity of Trichoplax. Studying this very evolutionarily derived organism will allow us to learn more about the processes and mechanisms of epithelial evolution and diversification in animals.