title: Experimental Approach Reveals the Role of alx1 in the Evolution of the Echinoderm Larval Skeleton.
abstract: Over the course of evolution, the acquisition of novel structures has ultimately led to wide variation in morphology among extant multicellular organisms. Thus, the origins of genetic systems for new morphological structures are a subject of great interest in evolutionary biology. The larval skeleton is a novel structure acquired in some echinoderm lineages via the activation of the adult skeletogenic machinery. Previously, VEGF signaling was suggested to have played an important role in the acquisition of the larval skeleton. In the present study, we compared expression patterns of Alx genes among echinoderm classes to further explore the factors involved in the acquisition of a larval skeleton. We found that the alx1 gene, originally described as crucial for sea urchin skeletogenesis, may have also played an essential role in the evolution of the larval skeleton. Unlike those echinoderms that have a larval skeleton, we found that alx1 of starfish was barely expressed in early larvae that have no skeleton. When alx1 overexpression was induced via injection of alx1 mRNA into starfish eggs, the expression patterns of certain genes, including those possibly involved in skeletogenesis, were altered. This suggested that a portion of the skeletogenic program was induced solely by alx1. However, we observed no obvious external phenotype or skeleton. We concluded that alx1 was necessary but not sufficient for the acquisition of the larval skeleton, which, in fact, requires several genetic events. Based on these results, we discuss how the larval expression of alx1 contributed to the acquisition of the larval skeleton in the putative ancestral lineage of echinoderms.
authors: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors: Hiroyuki
authors: H
authors: Koga
authors: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors: Haruka
authors: H
authors: Fujitani
authors: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors: Yoshiaki
authors: Y
authors: Morino
authors: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.|Institute of Biogeosciences, Japan Agency for Marine-Earth Science and Technology, Yokosuka, Japan.
authors: Norio
authors: N
authors: Miyamoto
authors: Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Japan.|Institute for Molecular Science of Medicine, Aichi Medical University, Nagakute, Japan.
authors: Jun
authors: J
authors: Tsuchimoto
authors: National Institute for Basic Biology, Okazaki, Japan.
authors: Tomoko F
authors: TF
authors: Shibata
authors: Center for Information Biology, National Institute of Genetics, Mishima, Japan.|Department of Genetics, The Graduate University for Advanced Studies, Mishima, Japan.
authors: Masafumi
authors: M
authors: Nozawa
authors: National Institute for Basic Biology, Okazaki, Japan.|School of Life Science, The Graduate University for Advanced Studies, Okazaki, Japan.
authors: Shuji
authors: S
authors: Shigenobu
authors: Nagahama Institute of Bio-Science and Technology, Nagahama, Japan.
authors: Atsushi
authors: A
authors: Ogura
authors: Graduate School of Bioscience, Tokyo Institute of Technology, Yokohama, Japan.
authors: Kazunori
authors: K
authors: Tachibana
authors: Marine and Coastal Research Center, Ochanomizu University, Tateyama, Japan.
authors: Masato
authors: M
authors: Kiyomoto
authors: Marine and Coastal Research Center, Ochanomizu University, Tateyama, Japan.|Department of Integrated Biosciences, Graduate School of Frontier Sciences, The University of Tokyo, Kashiwa, Japan.|Research and Education Center of Natural Sciences, Keio University, Yokohama, Japan.
authors: Shonan
authors: S
authors: Amemiya
authors: Graduate School of Life and Environmental Sciences, University of Tsukuba, Tsukuba, Japan.
authors: Hiroshi
authors: H
authors: Wada
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004447:Echinodermata / Q000235:genetics / Q000502:physiology*; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D018398:Homeodomain Proteins / Q000235:genetics* / Q000502:physiology*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007814:Larva / Q000235:genetics / Q000502:physiology; D010641:Phenotype; D010802:Phylogeny; D012616:Sea Cucumbers / Q000235:genetics / Q000502:physiology; D017423:Sequence Analysis, RNA; D013215:Starfish / Q000235:genetics* / Q000502:physiology*; D047270:Strongylocentrotus purpuratus / Q000235:genetics / Q000502:physiology; D042461:Vascular Endothelial Growth Factor A / Q000378:metabolism
chemical_list: D018398:Homeodomain Proteins; D042461:Vascular Endothelial Growth Factor A