The Experts below are selected from a list of 1020 Experts worldwide ranked by ideXlab platform
Xiaohong Wang - One of the best experts on this subject based on the ideXlab platform.
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biosilica aging from enzyme driven gelation via syneresis to chemical biochemical hardening
Biochimica et Biophysica Acta, 2013Co-Authors: Xiaohong Wang, Ute Schlosmacher, Heinz C Schroder, Michael Korzhev, Lei Jiang, Werner E. G. MüllerAbstract:Abstract Background The distinguished property of the Siliceous Sponge spicules is their enzyme (silicatein)-catalyzed biosilica formation. The enzymatically formed, non-structured biosilica product undergoes a molding, syneresis, and hardening process to form the species-specifically shaped, hard structured skeletal spicules. Besides of silicatein, a silicatein-associated protein, silintaphin-2, is assumed to be involved in the process of biosilica formation in vivo. Methods Biosilica has been synthesized enzymatically and determined quantitatively. In addition, the subsequent hardening/aging steps have been followed by spectroscopic and electron microscopic analyses. Results The young spicules, newly formed in Sponge cell aggregates, comprise high concentrations of sodium (~ 1 w/w %) and potassium (0.3%). During aging the two alkali metals are removed from the spicules by 80%. In parallel, water is withdrawn from the biosilica deposits. A protein, the silicatein-α interactor silintaphin-2, comprises clusters rich in the anionic amino acids aspartic acid [D] and glutamic acid [E]. The very acidic peptide was found to significantly enhance silica polymerization. This peptide also caused a strong aggregation of silicatein/biosilica particles. Conclusions The observations are explained by sodium ion removal from the initially formed biosilica deposits to the acidic amino acids in silintaphin-2. The crucial amino acids facilitating/forcing the silicatein-mediated biosilica reaction are D and E. General significance The data presented here provide a reaction mechanism that at neutral pH the extent of biosilica formation can be strongly intensified by the removal of cations. The results contribute to an understanding of the structuring process taking place during the formation of the solid spicule rods.
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hierarchical composition of the axial filament from spicules of the Siliceous Sponge suberites domuncula from biosilica synthesizing nanofibrils to structure and morphology guiding triangular stems
Cell and Tissue Research, 2013Co-Authors: Enrico Mugnaioli, Ute Schlosmacher, Heinz C Schroder, Marco Giovine, Ute Kolb, Xiaohong WangAbstract:The major structural and enzymatically active protein in spicules from Siliceous Sponges, e.g., for Suberites domuncula studied here, is silicatein. Silicatein has been established to be the key enzyme that catalyzes the formation of biosilica, a polymer that represents the inorganic scaffold for the spicule. In the present study, it is shown, by application of high-resolution transmission and scanning transmission electron microscopy that, during the initial phase of spicule synthesis, nanofibrils with a diameter of around 10 nm are formed that comprise bundles of between 10 and 20 nanofibrils. In intracellular vacuoles, silicasomes, the nanofibrils form polar structures with a pointed tip and a blunt end. In a time-dependent manner, these nanofibrillar bundles become embedded into a Si-rich matrix, indicative for the formation of biosilica via silicatein molecules that form the nanofibrils. These biosilicified nanofibrillar bundles become extruded from the intracellular space, where they are located in the silicasomes, to the extracellular environment by an evagination process, during which a cellular protrusion forms the axial canal in the growing spicule. The nanofibrillar bundles condense and progressively form the axial filament that becomes localized in the extracellular space. It is concluded that the silicatein-composing nanofibrils act not only as enzymatic silica bio-condensing platforms but also as a structure-giving guidance for the growing spicule.
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a cryptochrome based photosensory system in the Siliceous Sponge suberites domuncula demospongiae
FEBS Journal, 2010Co-Authors: Xiaohong Wang, Heinz C Schroder, Dario Pisignano, Klaus Peter Jochum, Vladislav A Grebenjuk, Michael Korzhev, Julia S Markl, Matthias WiensAbstract:Based on the light-reactive behavior of Siliceous Sponges, their intriguing quartz glass-based spicular system and the existence of a light-generating luciferase [Muller WEG et al. (2009) Cell Mol Life Sci 66, 537–552], a protein potentially involved in light reception has been identified, cloned and recombinantly expressed from the demoSponge Suberites domuncula. Its sequence displays two domains characteristic of cryptochrome, the N-terminal photolyase-related region and the C-terminal FAD-binding domain. The expression level of S. domuncula cryptochrome depends on animal’s exposure to light and is highest in tissue regions rich in Siliceous spicules; in the dark, no cryptochrome transcripts/translational products are seen. From the experimental data, it is proposed that Sponges might employ a luciferase-like protein, the spicular system and a cryptochrome as the light source, optical waveguide and photosensor, respectively.
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Sponges porifera as living metazoan witnesses from the neoproterozoic biomineralization and the concept of their evolutionary success
Terra Nova, 2010Co-Authors: Xiaohong Wang, Matthias Wiens, Lu Gan, Werner Ma E G LlerAbstract:Terra Nova, 22, 1–11, 2010 Abstract The emergence of the Metazoa can be dated back to the Neoproterozoic Era which comprises the Cryogenian Period during which two major glaciations occurred, the Sturtian and the Varanger-Marinoan. At that time, the phylum Porifera (Sponges) evolved as the first animals and developed a hard skeleton. The two classes of Siliceous Sponges, the Hexactinellida and the Demospongiae, are already provided with the major genetic repertoire and gene regulatory networks that also exist in modern multicellular animals. Besides these metazoan innovations, the Siliceous Sponges display one autapomorphic character, silicatein, an enzyme which mediates bio-silica formation. Well preserved Siliceous Sponge fossils have been excavated from the Cambrian Burgess Shale- and Chengjiang deposits. It is concluded that it was the hard skeleton of the Siliceous Sponges that contributed to the successful evolution and survival of the Porifera during the last 500 Ma.
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formation of giant spicules in the deep sea hexactinellid monorhaphis chuni schulze 1904 electron microscopic and biochemical studies
Cell and Tissue Research, 2007Co-Authors: Carsten Eckert, Klaus Kropf, Christopf Seckert, Ute Schlosmacher, Wolfgang Tremel, Xiaohong Wang, Stephan E Wolf, Heinz C SchroderAbstract:The Siliceous Sponge Monorhaphis chuni (Hexactinellida) synthesizes the largest biosilica structures on earth (3 m). Scanning electron microscopy has shown that these spicules are regularly composed of concentrically arranged lamellae (width: 3–10 μm). Between 400 and 600 lamellae have been counted in one giant basal spicule. An axial canal (diameter: ~2 μm) is located in the center of the spicules; it harbors the axial filament and is surrounded by an axial cylinder (100–150 μm) of electron-dense homogeneous silica. During dissolution of the spicules with hydrofluoric acid, the axial filament is first released followed by the release of a proteinaceous tubule. Two major proteins (150 kDa and 35 kDa) have been visualized, together with a 24-kDa protein that cross-reacts with antibodies against silicatein. The spicules are surrounded by a collagen net, and the existence of a hexactinellidan collagen gene has been demonstrated by cloning it from Aphrocallistes vastus. During the axial growth of the spicules, silicatein or the silicatein-related protein is proposed to become associated with the surface of the spicules and to be finally internalized through the apical opening to associate with the axial filament. Based on the data gathered here, we suggest that, in the Hexactinellida, the growth of the spicules is mediated by silicatein or by a silicatein-related protein, with the orientation of biosilica deposition being controlled by lectin and collagen.
Kevin J Peterson - One of the best experts on this subject based on the ideXlab platform.
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Where's the glass? Biomarkers, molecular clocks, and microRNAs suggest a 200-Myr missing Precambrian fossil record of Siliceous Sponge spicules
2020Co-Authors: E Sp A Erling, Jeffrey M Robinson, Kevin J PetersonAbstract:ABSTRACT The earliest evidence for animal life comes from the fossil record of 24-isopropylcholestane, a sterane found in Cryogenian deposits, and whose precursors are found in modern demoSponges, but not choanoflagellates, calcareans, hexactinellids, or eumetazoans. However, many modern demoSponges are also characterized by the presence of Siliceous spicules, and there are no convincing demoSponge spicules in strata older than the Cambrian. This temporal disparity highlights a problem with our understanding of the Precambrian fossil record -either these supposed demoSponge-specific biomarkers were derived from the sterols of some other organism and are simply retained in modern demoSponges, or spicules do not primitively characterize crown-group demoSponges. Resolving this issue requires resolving the phylogenetic placement of another group of Sponges, the hexactinellids, which not only make a spicule thought to be homologous to the spicules of demoSponges, but also make their first appearance near the Precambrian ⁄ Cambrian boundary. Using two independent analytical approaches and data sets -traditional molecular phylogenetic analyses and the presence or absence of specific microRNA genes -we show that demoSponges are monophyletic, and that hexactinellids are their sister group (together forming the Silicea). Thus, spicules must have evolved before the last common ancestor of all living siliceans, suggesting the presence of a significant gap in the silicean spicule fossil record. Molecular divergence estimates date the origin of this last common ancestor well within the Cryogenian, consistent with the biomarker record, and strongly suggests that Siliceous spicules were present during the Precambrian but were not preserved
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where s the glass biomarkers molecular clocks and micrornas suggest a 200 myr missing precambrian fossil record of Siliceous Sponge spicules
Geobiology, 2010Co-Authors: Erik A Sperling, Jeffrey M Robinson, Kevin J PetersonAbstract:The earliest evidence for animal life comes from the fossil record of 24-isopropylcholestane, a sterane found in Cryogenian deposits, and whose precursors are found in modern demoSponges, but not choanoflagellates, calcareans, hexactinellids, or eumetazoans. However, many modern demoSponges are also characterized by the presence of Siliceous spicules, and there are no convincing demoSponge spicules in strata older than the Cambrian. This temporal disparity highlights a problem with our understanding of the Precambrian fossil record ‐ either these supposed demoSponge-specific biomarkers were derived from the sterols of some other organism and are simply retained in modern demoSponges, or spicules do not primitively characterize crown-group demoSponges. Resolving this issue requires resolving the phylogenetic placement of another group of Sponges, the hexactinellids, which not only make a spicule thought to be homologous to the spicules of demoSponges, but also make their first appearance near the Precambrian ⁄Cambrian boundary. Using two independent analytical approaches and data sets ‐ traditional molecular phylogenetic analyses and the presence or absence of specific microRNA genes ‐ we show that demoSponges are monophyletic, and that hexactinellids are their sister group (together forming the Silicea). Thus, spicules must have evolved before the last common ancestor of all living siliceans, suggesting the presence of a significant gap in the silicean spicule fossil record. Molecular divergence estimates date the origin of this last common ancestor well within the Cryogenian, consistent with the biomarker record, and strongly suggests that Siliceous spicules were present during the Precambrian but were not preserved.
Matthias Wiens - One of the best experts on this subject based on the ideXlab platform.
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advances in research on Siliceous Sponge spicules novel insight into the understanding of biomineralization mechanisms and bionic applications
Acta Geoscientica Sinica, 2011Co-Authors: X H Wang, Ute Schlosmacher, Heinz C Schroder, Matthias Wiens, Klaus Peter Jochum, Shunfeng Wang, F Zhou, Werner E. G. MüllerAbstract:Siliceous Sponges are the simplest and oldest multi-cellular animals on the Earth.They achieved a perfect technical blueprint during their million years of evolution.A new energy-saving and environmentally friendly technology has been developed by nature for human applications allowing the production of novel bio-inorganic mineral materials using nano-biotechnological approaches.There is a wide application prospect in the fields of optical fibers,microelectronics,biomedical materials and some further areas.Monorhaphis chuni lives in the deep sea over 1000 m in depth.Its giant basal spicule is growing to a length of 3 m and is therefore the largest bio-silica structure on the Earth.It is a highly suitable model for the study of bio-silicification mechanisms and for their bionic applications.In this paper,the authors systematically summarize the research progress in these giant basal spicules on the following topics:structure,composition,mechanical properties,optophysical properties,biochemical properties and molecular biological basis,biomineralization mechanism as well as bionic applications in biomedicine.
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a cryptochrome based photosensory system in the Siliceous Sponge suberites domuncula demospongiae
FEBS Journal, 2010Co-Authors: Xiaohong Wang, Heinz C Schroder, Dario Pisignano, Klaus Peter Jochum, Vladislav A Grebenjuk, Michael Korzhev, Julia S Markl, Matthias WiensAbstract:Based on the light-reactive behavior of Siliceous Sponges, their intriguing quartz glass-based spicular system and the existence of a light-generating luciferase [Muller WEG et al. (2009) Cell Mol Life Sci 66, 537–552], a protein potentially involved in light reception has been identified, cloned and recombinantly expressed from the demoSponge Suberites domuncula. Its sequence displays two domains characteristic of cryptochrome, the N-terminal photolyase-related region and the C-terminal FAD-binding domain. The expression level of S. domuncula cryptochrome depends on animal’s exposure to light and is highest in tissue regions rich in Siliceous spicules; in the dark, no cryptochrome transcripts/translational products are seen. From the experimental data, it is proposed that Sponges might employ a luciferase-like protein, the spicular system and a cryptochrome as the light source, optical waveguide and photosensor, respectively.
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Sponges porifera as living metazoan witnesses from the neoproterozoic biomineralization and the concept of their evolutionary success
Terra Nova, 2010Co-Authors: Xiaohong Wang, Matthias Wiens, Lu Gan, Werner Ma E G LlerAbstract:Terra Nova, 22, 1–11, 2010 Abstract The emergence of the Metazoa can be dated back to the Neoproterozoic Era which comprises the Cryogenian Period during which two major glaciations occurred, the Sturtian and the Varanger-Marinoan. At that time, the phylum Porifera (Sponges) evolved as the first animals and developed a hard skeleton. The two classes of Siliceous Sponges, the Hexactinellida and the Demospongiae, are already provided with the major genetic repertoire and gene regulatory networks that also exist in modern multicellular animals. Besides these metazoan innovations, the Siliceous Sponges display one autapomorphic character, silicatein, an enzyme which mediates bio-silica formation. Well preserved Siliceous Sponge fossils have been excavated from the Cambrian Burgess Shale- and Chengjiang deposits. It is concluded that it was the hard skeleton of the Siliceous Sponges that contributed to the successful evolution and survival of the Porifera during the last 500 Ma.
Isabelle Domartcoulon - One of the best experts on this subject based on the ideXlab platform.
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calcareous Sponge biomineralization ultrastructural and compositional heterogeneity of spicules in leuconia johnstoni carter 1871
Journal of Structural Biology, 2011Co-Authors: C Kopp, Jaroslaw Stolarski, Olivier Beyssac, Anders Meibom, Shakib Djediat, Jakub Szlachetko, Isabelle DomartcoulonAbstract:In contrast to Siliceous Sponge spicules, the biomineralization in calcareous Sponges is poorly understood. In particular, the existence of a differentiated central core in calcareous spicules is still controversial. Here we combine high-spatial resolution analyses, including NanoSIMS, Raman, SXM, AFM, SEM and TEM to investigate the composition, mineralogy and ultrastructure of the giant tetractines of Leuconia johnstoni Carter, 1871 (Baeriidae, Calcaronea) and the organization of surrounding cells. A compositionally distinct core is present in these spicule types. The core measures 3.5-10 mu m in diameter and is significantly depleted in Mg and lightly enriched in S compared with the adjacent outer layer in the spicule. Measured Mg/Ca ratios in the core range from 70 to 90 mmol/mol compared to 125-130 mmol/mol in the adjacent calcite envelope. However, this heterogeneous distribution of Mg and S is not reflected in the mineralogy and the microstructure. Raman spectroscopy demonstrates a purely calcitic mineralogy. SEM examination of slightly etched spicules indicates an ultrastructure organized hierarchically in a concentric pattern, with layers less than 250 nm in width inside layers averaging 535 +/- 260 nm. No change in structural pattern corresponds to the Mg/Ca variation observed. AFM and TEM observations show a nano-granular organization of the spicules with a network of intraspicular organic material intercalated between nanograins 60-130 nm in diameter. Observations of sclerocyte cells in the process of spiculogenesis suggest that the compositionally distinct core is produced by a sub-apical sclerocyte "founder cell" that controls axial growth, while the envelope is secreted by lateral sclerocytes "thickener cells", which control radial growth. (C) 2010 Elsevier Inc. All rights reserved.
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calcareous Sponge biomineralization ultrastructural and compositional heterogeneity of spicules in leuconia johnstoni
Journal of Structural Biology, 2011Co-Authors: C Kopp, Jaroslaw Stolarski, Olivier Beyssac, Anders Meibom, Shakib Djediat, Jakub Szlachetko, Isabelle DomartcoulonAbstract:In contrast to Siliceous Sponge spicules, the biomineralization in calcareous Sponges is poorly understood. In particular, the existence of a differentiated central core in calcareous spicules is still controversial. Here we combine high-spatial resolution analyses, including NanoSIMS, Raman, SXM, AFM, SEM and TEM to investigate the composition, mineralogy and ultrastructure of the giant tetractines of Leuconia johnstoni Carter, 1871 (Baeriidae, Calcaronea) and the organization of surrounding cells. A compositionally distinct core is present in these spicule types. The core measures 3.5-10 mu m in diameter and is significantly depleted in Mg and lightly enriched in S compared with the adjacent outer layer in the spicule. Measured Mg/Ca ratios in the core range from 70 to 90 mmol/mol compared to 125-130 mmol/mol in the adjacent calcite envelope. However, this heterogeneous distribution of Mg and S is not reflected in the mineralogy and the microstructure. Raman spectroscopy demonstrates a purely calcitic mineralogy. SEM examination of slightly etched spicules indicates an ultrastructure organized hierarchically in a concentric pattern, with layers less than 250 nm in width inside layers averaging 535 +/- 260 nm. No change in structural pattern corresponds to the Mg/Ca variation observed. AFM and TEM observations show a nano-granular organization of the spicules with a network of intraspicular organic material intercalated between nanograins 60-130 nm in diameter. Observations of sclerocyte cells in the process of spiculogenesis suggest that the compositionally distinct core is produced by a sub-apical sclerocyte "founder cell" that controls axial growth, while the envelope is secreted by lateral sclerocytes "thickener cells", which control radial growth. (C) 2010 Elsevier Inc. All rights reserved.
Heinz C Schroder - One of the best experts on this subject based on the ideXlab platform.
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biosilica aging from enzyme driven gelation via syneresis to chemical biochemical hardening
Biochimica et Biophysica Acta, 2013Co-Authors: Xiaohong Wang, Ute Schlosmacher, Heinz C Schroder, Michael Korzhev, Lei Jiang, Werner E. G. MüllerAbstract:Abstract Background The distinguished property of the Siliceous Sponge spicules is their enzyme (silicatein)-catalyzed biosilica formation. The enzymatically formed, non-structured biosilica product undergoes a molding, syneresis, and hardening process to form the species-specifically shaped, hard structured skeletal spicules. Besides of silicatein, a silicatein-associated protein, silintaphin-2, is assumed to be involved in the process of biosilica formation in vivo. Methods Biosilica has been synthesized enzymatically and determined quantitatively. In addition, the subsequent hardening/aging steps have been followed by spectroscopic and electron microscopic analyses. Results The young spicules, newly formed in Sponge cell aggregates, comprise high concentrations of sodium (~ 1 w/w %) and potassium (0.3%). During aging the two alkali metals are removed from the spicules by 80%. In parallel, water is withdrawn from the biosilica deposits. A protein, the silicatein-α interactor silintaphin-2, comprises clusters rich in the anionic amino acids aspartic acid [D] and glutamic acid [E]. The very acidic peptide was found to significantly enhance silica polymerization. This peptide also caused a strong aggregation of silicatein/biosilica particles. Conclusions The observations are explained by sodium ion removal from the initially formed biosilica deposits to the acidic amino acids in silintaphin-2. The crucial amino acids facilitating/forcing the silicatein-mediated biosilica reaction are D and E. General significance The data presented here provide a reaction mechanism that at neutral pH the extent of biosilica formation can be strongly intensified by the removal of cations. The results contribute to an understanding of the structuring process taking place during the formation of the solid spicule rods.
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hierarchical composition of the axial filament from spicules of the Siliceous Sponge suberites domuncula from biosilica synthesizing nanofibrils to structure and morphology guiding triangular stems
Cell and Tissue Research, 2013Co-Authors: Enrico Mugnaioli, Ute Schlosmacher, Heinz C Schroder, Marco Giovine, Ute Kolb, Xiaohong WangAbstract:The major structural and enzymatically active protein in spicules from Siliceous Sponges, e.g., for Suberites domuncula studied here, is silicatein. Silicatein has been established to be the key enzyme that catalyzes the formation of biosilica, a polymer that represents the inorganic scaffold for the spicule. In the present study, it is shown, by application of high-resolution transmission and scanning transmission electron microscopy that, during the initial phase of spicule synthesis, nanofibrils with a diameter of around 10 nm are formed that comprise bundles of between 10 and 20 nanofibrils. In intracellular vacuoles, silicasomes, the nanofibrils form polar structures with a pointed tip and a blunt end. In a time-dependent manner, these nanofibrillar bundles become embedded into a Si-rich matrix, indicative for the formation of biosilica via silicatein molecules that form the nanofibrils. These biosilicified nanofibrillar bundles become extruded from the intracellular space, where they are located in the silicasomes, to the extracellular environment by an evagination process, during which a cellular protrusion forms the axial canal in the growing spicule. The nanofibrillar bundles condense and progressively form the axial filament that becomes localized in the extracellular space. It is concluded that the silicatein-composing nanofibrils act not only as enzymatic silica bio-condensing platforms but also as a structure-giving guidance for the growing spicule.
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advances in research on Siliceous Sponge spicules novel insight into the understanding of biomineralization mechanisms and bionic applications
Acta Geoscientica Sinica, 2011Co-Authors: X H Wang, Ute Schlosmacher, Heinz C Schroder, Matthias Wiens, Klaus Peter Jochum, Shunfeng Wang, F Zhou, Werner E. G. MüllerAbstract:Siliceous Sponges are the simplest and oldest multi-cellular animals on the Earth.They achieved a perfect technical blueprint during their million years of evolution.A new energy-saving and environmentally friendly technology has been developed by nature for human applications allowing the production of novel bio-inorganic mineral materials using nano-biotechnological approaches.There is a wide application prospect in the fields of optical fibers,microelectronics,biomedical materials and some further areas.Monorhaphis chuni lives in the deep sea over 1000 m in depth.Its giant basal spicule is growing to a length of 3 m and is therefore the largest bio-silica structure on the Earth.It is a highly suitable model for the study of bio-silicification mechanisms and for their bionic applications.In this paper,the authors systematically summarize the research progress in these giant basal spicules on the following topics:structure,composition,mechanical properties,optophysical properties,biochemical properties and molecular biological basis,biomineralization mechanism as well as bionic applications in biomedicine.
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a cryptochrome based photosensory system in the Siliceous Sponge suberites domuncula demospongiae
FEBS Journal, 2010Co-Authors: Xiaohong Wang, Heinz C Schroder, Dario Pisignano, Klaus Peter Jochum, Vladislav A Grebenjuk, Michael Korzhev, Julia S Markl, Matthias WiensAbstract:Based on the light-reactive behavior of Siliceous Sponges, their intriguing quartz glass-based spicular system and the existence of a light-generating luciferase [Muller WEG et al. (2009) Cell Mol Life Sci 66, 537–552], a protein potentially involved in light reception has been identified, cloned and recombinantly expressed from the demoSponge Suberites domuncula. Its sequence displays two domains characteristic of cryptochrome, the N-terminal photolyase-related region and the C-terminal FAD-binding domain. The expression level of S. domuncula cryptochrome depends on animal’s exposure to light and is highest in tissue regions rich in Siliceous spicules; in the dark, no cryptochrome transcripts/translational products are seen. From the experimental data, it is proposed that Sponges might employ a luciferase-like protein, the spicular system and a cryptochrome as the light source, optical waveguide and photosensor, respectively.
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formation of giant spicules in the deep sea hexactinellid monorhaphis chuni schulze 1904 electron microscopic and biochemical studies
Cell and Tissue Research, 2007Co-Authors: Carsten Eckert, Klaus Kropf, Christopf Seckert, Ute Schlosmacher, Wolfgang Tremel, Xiaohong Wang, Stephan E Wolf, Heinz C SchroderAbstract:The Siliceous Sponge Monorhaphis chuni (Hexactinellida) synthesizes the largest biosilica structures on earth (3 m). Scanning electron microscopy has shown that these spicules are regularly composed of concentrically arranged lamellae (width: 3–10 μm). Between 400 and 600 lamellae have been counted in one giant basal spicule. An axial canal (diameter: ~2 μm) is located in the center of the spicules; it harbors the axial filament and is surrounded by an axial cylinder (100–150 μm) of electron-dense homogeneous silica. During dissolution of the spicules with hydrofluoric acid, the axial filament is first released followed by the release of a proteinaceous tubule. Two major proteins (150 kDa and 35 kDa) have been visualized, together with a 24-kDa protein that cross-reacts with antibodies against silicatein. The spicules are surrounded by a collagen net, and the existence of a hexactinellidan collagen gene has been demonstrated by cloning it from Aphrocallistes vastus. During the axial growth of the spicules, silicatein or the silicatein-related protein is proposed to become associated with the surface of the spicules and to be finally internalized through the apical opening to associate with the axial filament. Based on the data gathered here, we suggest that, in the Hexactinellida, the growth of the spicules is mediated by silicatein or by a silicatein-related protein, with the orientation of biosilica deposition being controlled by lectin and collagen.