title: Bio-sintering processes in hexactinellid sponges: fusion of bio-silica in giant basal spicules from Monorhaphis chuni.
abstract: The two sponge classes, Hexactinellida and Demospongiae, comprise a skeleton that is composed of siliceous skeletal elements (spicules). Spicule growth proceeds by appositional layering of lamellae that consist of silica nanoparticles, which are synthesized via the sponge-specific enzyme silicatein. While in demosponges during maturation the lamellae consolidate to a solid rod, the lamellar organization of hexactinellid spicules largely persists. However, the innermost lamellae, near the spicule core, can also fuse to a solid axial cylinder. Similar to the fusion of siliceous nanoparticles and lamella, in several hexactinellid species individual spicules unify during sintering-like processes. Here, we study the different stages of a process that we termed bio-sintering, within the giant basal spicule (GBS) of Monorhaphis chuni. During this study, a major GBS protein component (27 kDa) was isolated and analyzed by MALDI-TOF-MS. The sequences were used to isolate and clone the encoding cDNA via degenerate primer PCR. Bioinformatic analyses revealed a significant sequence homology to silicatein. In addition, the native GBS protein was able to mediate bio-silica synthesis in vitro. We conclude that the syntheses of bio-silica in M. chuni, and the subsequent fusion of nanoparticles to lamellae, and finally to spicules, are enzymatically-driven by a silicatein-like protein. In addition, evidence is now presented that in hexactinellids those fusions involve sintering-like processes.
authors.affiliation: Institute for Physiological Chemistry and Pathobiochemistry, Medical School, Johannes Gutenberg-University, Mainz, Germany. wmueller@uni-mainz.de
authors.forename: Werner E G
authors.initials: WE
authors.lastname: Müller
authors.forename: Xiaohong
authors.initials: X
authors.lastname: Wang
authors.forename: Zaklina
authors.initials: Z
authors.lastname: Burghard
authors.forename: Joachim
authors.initials: J
authors.lastname: Bill
authors.forename: Anatoli
authors.initials: A
authors.lastname: Krasko
authors.forename: Alexandra
authors.initials: A
authors.lastname: Boreiko
authors.forename: Ute
authors.initials: U
authors.lastname: Schlossmacher
authors.forename: Heinz C
authors.initials: HC
authors.lastname: Schröder
authors.forename: Matthias
authors.initials: M
authors.lastname: Wiens
mesh_terms: D000825:Animal Structures / Q000033:anatomy & histology* / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D000818:Animals; D015152:Blotting, Northern; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D011161:Porifera / Q000033:anatomy & histology* / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D012822:Silicon Dioxide / Q000737:chemistry / Q000378:metabolism*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D012822:Silicon Dioxide