6533b7d3fe1ef96bd125ffe8

RESEARCH PRODUCT

Hardening of bio-silica in sponge spicules involves an aging process after its enzymatic polycondensation: evidence for an aquaporin-mediated water absorption.

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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. General significance 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.