title: Expression patterns of Hox genes in larvae of the sea lily Metacrinus rotundus.
abstract: We cloned eight Hox genes (MrHox1, MrHox2, MrHox4, MrHox5, MrHox7, MrHox8, MrHox9/10, and MrHox11/13c) from the sea lily Metacrinus rotundus, a member of the most basal group of the extant echinoderms. At the auricularia stage, before the formation of the pentaradial rudiment, four MrHox genes were expressed sequentially along the anteroposterior (AP) axis in the straightened mesodermal somatocoels in the order MrHox5, MrHox7, MrHox8, and MrHox9/10. The expression of MrHox7 and MrHox8 was detected as early as the hatching stage in the presumptive somatocoel region of the archenteral sac. MrHox5 was expressed in the anteriormost region of the somatocoels, where a stalk-related structure (the chambered organ) forms later. In addition to the mesodermal somatocoels, MrHox7 was expressed in the oral hood ectoderm, which gives rise to the adhesive pit. The expression of four other MrHox genes (MrHox1, MrHox2, MrHox4, and MrHox11/13c) was not detected in any of the larval stages we examined. In comparison with the mesodermal sea urchin Hox genes, the MrHox genes are expressed more posteriorly along the AP (oral-anal) axis than the sea urchin orthologs, implying that the evolution of the eleutherozoans was accompanied by a posteriorization of the larval body. Our study illuminates the possible body plan and Hox expression patterns of the ancestral echinoderm and sheds light on the larval body plan of the last common ancestor of the echinoderms and chordates.
authors.affiliation: Department of Biological Sciences, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan.
authors.forename: Yuko
authors.initials: Y
authors.lastname: Hara
authors.forename: Masaaki
authors.initials: M
authors.lastname: Yamaguchi
authors.forename: Koji
authors.initials: K
authors.lastname: Akasaka
authors.forename: Hiroaki
authors.initials: H
authors.lastname: Nakano
authors.forename: Masaru
authors.initials: M
authors.lastname: Nonaka
authors.forename: Shonan
authors.initials: S
authors.lastname: Amemiya
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019521:Body Patterning; D003001:Cloning, Molecular; D004447:Echinodermata / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000737:chemistry / Q000235:genetics; D017403:In Situ Hybridization; D007814:Larva / Q000235:genetics / Q000378:metabolism; D008648:Mesoderm / Q000502:physiology; D008954:Models, Biological; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid
chemical_list: D018398:Homeodomain Proteins