title: Evolution of metazoan cell junction proteins: the scaffold protein MAGI and the transmembrane receptor tetraspanin in the demosponge Suberites domuncula.
abstract: Until recently the positioning of the sponges (phylum Porifera) within the metazoan systematics was hampered by the lack of molecular evidence for the existence of junctional structures in the surface cell layers. In this study two genes related to the tight junctions are characterized from the demosponge Suberites domuncula: tetraspanin (SDTM4SF), a cell surface receptor, and MAGI (SDMAGI), a MAGUK (membrane-associated guanylate kinase homologue) protein. Especially the MAGI protein is known in other metazoan animal phyla to exist exclusively in tight junctions. The characteristic domains of MAGI proteins (six PDZ domains, two WW domains, and a truncated guanylate kinase motif) are conserved in the sponge protein. The functional analysis of SDMAGI done by in situ hybridization shows its expression in the surface epithelial layers (exopinacoderm and endopinacoderm). Northern blot studies reveal that expression of SDMAGI and SDTM4SF increases after formation of the pinacoderm layer in the animals as well as in primmorphs. These results support earlier notions that sponges contain junctional structures. We conclude that sponges contain epithelia whose cells are organized by cell junctions.
authors.affiliation: Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, Duesbergweg 6, D-55099, Mainz, Germany.
authors.forename: Teresa
authors.initials: T
authors.lastname: Adell
authors.forename: Vera
authors.initials: V
authors.lastname: Gamulin
authors.forename: Sanja
authors.initials: S
authors.lastname: Perović-Ottstadt
authors.forename: Matthias
authors.initials: M
authors.lastname: Wiens
authors.forename: Michael
authors.initials: M
authors.lastname: Korzhev
authors.forename: Isabel M
authors.initials: IM
authors.lastname: Müller
authors.forename: Werner E G
authors.initials: WE
authors.lastname: Müller
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D018076:DNA, Complementary / Q000235:genetics; D019143:Evolution, Molecular; D015870:Gene Expression; D051528:Guanylate Kinases; D017403:In Situ Hybridization; D007365:Intercellular Junctions / Q000235:genetics*; D008522:Mediterranean Sea; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D009703:Nucleoside-Phosphate Kinase / Q000235:genetics; D010802:Phylogeny; D011161:Porifera / Q000235:genetics*; D017434:Protein Structure, Tertiary; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
chemical_list: D018076:DNA, Complementary; D008565:Membrane Proteins; D009703:Nucleoside-Phosphate Kinase; D051528:Guanylate Kinases