Gap junctions in Nematostella vectensis sea anemone embryos

Abstract

Gap junctions (GJs) are composed of membrane protein molecules and form intercellular channels that connect the cytoplasm of adjacent cells and are permeable to ions and small molecules. Gap junctions are found in different types of organisms and are considered to be a universal feature of all multicellular animals (Metazoa). Until recently, sea anemones and corals (Anthozoa) have appeared to be an exception from this rule. There were no structural or physiological data that support the presence of GJs in Anthozoa. No genes homologous to any of the two groups of the known GJ proteins, such as connexins and pannexins, were found in the genomes of the sea anemone Nematostella vectensis (Cnidaria, Anthozoa) or other Anthozoa animals. Lately, a homolog of pannexin was found in Nematostella; moreover, our physiological experiments demonstrated electrical coupling between blastomeres in embryos at the eight-cell stage. In addition, a fluorescent dye (carboxyfluorescein) showed no diffusion between electrically coupled cells, which excludes the possibility that the observed electrical coupling is mediated via incomplete cytoplasm separation during the cleavage. The obtained data support the idea that GJs are ubiquitous for Metazoa, whereas pannexins are universal GJ proteins.