Cadherin switch marks germ layer formation in the diploblastic sea anemone Nematostella vectensis

Morphogenesisis a shape-building process during development of multicellular organisms. During this process the establishment and modulation of cell-cell contacts play an important role. Cadherins, the major cell adhesion molecules, form adherens junctionsconnecting epithelial cells. Numerous studies in Bilateriahave shown that cadherinsare associated with the regulation of cell differentiation, cell shape changes, cell migration and tissue morphogenesis. To date, the role of Cadherinsin non-bilaterians is unknown. Here, we study the expression and the function of two paralogous classical cadherins, cadherin1 and cadherin3, in the diploblastic animal, the sea anemone Nematostellavectensis. We show that a cadherinswitch is accompanying the formation of germ layers. Using specific antibodies, we show that both cadherinsare localized to adherens junctionsat apical and basal positions in ectodermand endoderm. During gastrulation, partial EMT of endodermalcells is marked by a step-wise down-regulation of cadherin3 and up-regulation of cadherin1. Knockdown experiments show that both cadherinsare required for maintenance of tissue integrity and tissue morphogenesis. Thus, both sea anemonesand bilaterians use independently duplicated cadherinscombinatorially for tissue morphogenesisand germ layerdifferentiation.