title: Hardening of bio-silica in sponge spicules involves an aging process after its enzymatic polycondensation: evidence for an aquaporin-mediated water absorption.
abstract: BACKGROUND
  Spicules, the siliceous skeletal elements of the siliceous sponges, are synthesized enzymatically via silicatein. The product formed, bio-silica, constitutes their inorganic matrix. It remained unexplored which reactions are involved in molding of the amorphous bio-silica and formation of a solid and rigid biomaterial.
  
  
  METHODS
  Cell and molecular biological techniques have been applied to analyze processes resulting in the hardening of the enzymatically synthesized bio-silica. The demosponge Suberites domuncula has been used for the studies.
  
  
  RESULTS
  Cell aggregates (primmorphs) from the sponge S. domuncula, grown in the presence of Mn-sulfate, form spicules that comprise, instead of a smooth, a rough and porous surface which is decorated with irregular bio-silica deposits. During this process, the expression of the aquaporin-8 gene becomes down-regulated. Further in vitro studies showed that aquaporin is required for dehydration, and hardening of bio-silica following its enzymatic formation. The data show that in cell aggregates grown in the presence of Mn-sulfate, aquaporin-8 is down-regulated. We conclude that in cell aggregates grown in the presence of Mn-sulfate, the removal of reaction water, produced during the bio-silica polycondensation reaction, is inhibited.
  
  
  CONCLUSIONS
  This study highlights that besides the silicatein-driven polycondensation reaction, the spicule formation also requires a phase of syneresis that results in a hardening of the material.
authors.affiliation: ERC Advanced Grant Research Group at the Institute for Physiological Chemistry, University Medical Center of the Johannes Gutenberg University, Duesbergweg 6, D-55128 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: Matthias
authors.initials: M
authors.lastname: Wiens
authors.forename: Ute
authors.initials: U
authors.lastname: Schlossmacher
authors.forename: Klaus Peter
authors.initials: KP
authors.lastname: Jochum
authors.forename: Heinz C
authors.initials: HC
authors.lastname: Schröder
mesh_terms: D000042:Absorption / Q000187:drug effects; D000595:Amino Acid Sequence; D000818:Animals; D020346:Aquaporins / Q000145:classification / Q000235:genetics / Q000378:metabolism*; D002403:Cathepsins / Q000235:genetics / Q000378:metabolism; D005455:Fluorescent Antibody Technique; D015870:Gene Expression / Q000187:drug effects; D008278:Magnesium Sulfate / Q000494:pharmacology; D008855:Microscopy, Electron, Scanning; D008969:Molecular Sequence Data; D044367:Phase Transition / Q000187:drug effects; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017386:Sequence Homology, Amino Acid; D012822:Silicon Dioxide / Q000737:chemistry / Q000378:metabolism*; D013052:Spectrometry, X-Ray Emission; D047233:Suberites / Q000235:genetics / Q000378:metabolism* / Q000648:ultrastructure; D013997:Time Factors; D014867:Water / Q000378:metabolism*
chemical_list: D020346:Aquaporins; C112571:silicatein alpha; D014867:Water; D008278:Magnesium Sulfate; D012822:Silicon Dioxide; D002403:Cathepsins