title: A novel amphioxus cadherin that localizes to epithelial adherens junctions has an unusual domain organization with implications for chordate phylogeny.
abstract: Although data are available from only vertebrates, urochordates, and three nonchordate animals, there are definite differences in the structures of classic cadherins between vertebrates plus urochordates and nonchordates. In this study we examined structural diversity of classic cadherins among bilaterian animals by obtaining new data from an amphioxus (Cephalochordata, Chordata), an acorn worm (Hemichordata), a sea star (Echinodermata), and an oyster (Mollusca). The structures of newly identified nonchordate cadherins are grouped together with those of the known sea urchin and Drosophila cadherins, whereas the structure of an amphioxus (Branchiostoma belcheri) cadherin, designated BbC, is differently categorized from those of other known chordate cadherins. BbC is identified as a cadherin by its cytoplasmic domain whose sequence is highly related to the cytoplasmic sequences of all known classic cadherins, but it lacks all of the five repeats constituting the extracellular homophilic-binding domain of other chordate cadherins. The ectodomains of BbC match the ectodomains found in nonchordate cadherins but not present in other chordate cadherins. We show that the BbC functions as a cell-cell adhesion molecule when expressed in Drosophila S2 cells and localizes to adherens junctions in the ectodermal epithelia in amphioxus embryos. We argue that BbC is the amphioxus homologue of the classic cadherins involved in the formation of epithelial adherens junctions. The structural relationships of the cadherin molecules allow us to propose a possibility that cephalochordates might be basal to the sister-groups vertebrates and urochordates.
authors.affiliation: Tsukita Cell Axis Project, ERATO, Japan Science and Technology Corporation, Yoshidakonoe-cho, Sakyo-ku, Kyoto 606-8501, Japan. hoda@brh.co.jp
authors.forename: Hiroki
authors.initials: H
authors.lastname: Oda
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Wada
authors.forename: Kunifumi
authors.initials: K
authors.lastname: Tagawa
authors.forename: Yasuko
authors.initials: Y
authors.lastname: Akiyama-Oda
authors.forename: Nori
authors.initials: N
authors.lastname: Satoh
authors.forename: Tom
authors.initials: T
authors.lastname: Humphreys
authors.forename: Shicui
authors.initials: S
authors.lastname: Zhang
authors.forename: Shoichiro
authors.initials: S
authors.lastname: Tsukita
mesh_terms: D022005:Adherens Junctions / Q000235:genetics* / Q000378:metabolism*; D000595:Amino Acid Sequence; D000818:Animals; D015820:Cadherins / Q000235:genetics* / Q000378:metabolism; D002816:Chordata, Nonvertebrate / Q000235:genetics* / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D008969:Molecular Sequence Data; D010125:Ostreidae / Q000235:genetics; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D013215:Starfish / Q000235:genetics; D014714:Vertebrates / Q000235:genetics
chemical_list: D015820:Cadherins