title: Dynamic Transport and Cementation of Skeletal Elements Build Up the Pole-and-Beam Structured Skeleton of Sponges.
abstract: Animal bodies are shaped by skeletons, which are built inside the body by biomineralization of condensed mesenchymal cells in vertebrates [1, 2] and echinoderms [3, 4], or outside the body by apical secretion of extracellular matrices by epidermal cell layers in arthropods [5]. In each case, the skeletons' shapes are a direct reflection of the pattern of skeleton-producing cells [6]. Here we report a newly discovered mode of skeleton formation: assembly of sponges' mineralized skeletal elements (spicules) in locations distant from where they were produced. Although it was known that internal skeletons of sponges consist of spicules assembled into large pole-and-beam structures with a variety of morphologies [7-10], the spicule assembly process (i.e., how spicules become held up and connected basically in staggered tandem) and what types of cells act in this process remained unexplored. Here we found that mature spicules are dynamically transported from where they were produced and then pierce through outer epithelia, and their basal ends become fixed to substrate or connected with such fixed spicules. Newly discovered "transport cells" mediate spicule movement and the "pierce" step, and collagen-secreting basal-epithelial cells fix spicules to the substratum, suggesting that the processes of spiculous skeleton construction are mediated separately by specialized cells. Division of labor by manufacturer, transporter, and cementer cells, and iteration of the sequential mechanical reactions of "transport," "pierce," "raise up," and "cementation," allows construction of the spiculous skeleton spicule by spicule as a self-organized biological structure, with the great plasticity in size and shape required for indeterminate growth, and generating the great morphological diversity of individual sponges.
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Sohei
authors.initials: S
authors.lastname: Nakayama
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kazushi
authors.initials: K
authors.lastname: Arima
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kotoe
authors.initials: K
authors.lastname: Kawai
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kurato
authors.initials: K
authors.lastname: Mohri
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Chihiro
authors.initials: C
authors.lastname: Inui
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Wakana
authors.initials: W
authors.lastname: Sugano
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Hibiki
authors.initials: H
authors.lastname: Koba
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kentaro
authors.initials: K
authors.lastname: Tamada
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Yudai J
authors.initials: YJ
authors.lastname: Nakata
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kouji
authors.initials: K
authors.lastname: Kishimoto
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Miyuki
authors.initials: M
authors.lastname: Arai-Shindo
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Chiaki
authors.initials: C
authors.lastname: Kojima
authors.affiliation: Department of Mechanical Engineering, Graduate School of Engineering, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya, Aichi 466-8555, Japan.
authors.forename: Takeo
authors.initials: T
authors.lastname: Matsumoto
authors.affiliation: Division of Embryology, National Institute of Basic Biology, 5-1 Higashiyama, Myodaiji, Okazaki, Aichi 444-8787, Japan.
authors.forename: Toshihiko
authors.initials: T
authors.lastname: Fujimori
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan.
authors.forename: Kiyokazu
authors.initials: K
authors.lastname: Agata
authors.affiliation: Department of Biophysics, Graduate School of Science, Kyoto University, Kitashirakawa-oiwake, Sakyo-ku, Kyoto 606-8502, Japan; Precursory Research for Embryonic Science and Technology (PRESTO) Program, Japan Science and Technology Agency (JST), 4-1-8 Honcho, Kawaguchi, Saitama 332-0012, Japan. Electronic address: funayama@mdb.biophys.kyoto-u.ac.jp.
authors.forename: Noriko
authors.initials: N
authors.lastname: Funayama
mesh_terms: D000818:Animals; D002484:Cementation; D003094:Collagen / Q000378:metabolism; D004848:Epithelium / Q000378:metabolism; D008903:Minerals / Q000378:metabolism; D011161:Porifera / Q000254:growth & development* / Q000378:metabolism*; D012863:Skeleton
chemical_list: D008903:Minerals; D003094:Collagen