Gap junctions in sea anemone, Nematostella vectensis, embryo

Gap junctions (GJs) are composed of membrane proteins that form channels connecting the cytoplasm of adjacent cells and permeable to ions and small molecules. They are considered to be the main or only type of intercellular channels and a universal feature of all multicellular animals (Metazoa). Till recently, sea anemones and corals (Anthozoa, Cnidaria) appeared to be an exception from this rule. There were no structural or physiological data supporting the presence of GJ in Anthozoa. For some time no genes homologous to GJ proteins (connexins or pannexins) were detected in sea anemone Nematostella vectensis (Cnidaria, Anthozoa) or other Anthozoa genomes. Recently, pannexin homolog was found in Nematostella. Our intracellular recordings demonstrate electrical coupling between blastomeres in embryos at the 8-cells stage. At the same time, carboxyfluorescein fluorescent dye did not diffuse between electrically coupled cells, which excludes the possibility that the observed electrical coupling is mediated by incomplete cytoplasm separation during the cleavage. These data support the idea that GJ are ubiquitous for Metazoa, and pannexins are universal GJ proteins.