Co-expression and Functional Interaction of Silicatein with Galectin

Abstract

Sponges (phylum Porifera) of the class of Demospongiae are stabilized by a siliceous skeleton. It is composed of silica needles (spicules), which provide the morphogenetic scaffold of these metazoans. In the center of the spicules there is an axial filament that consists predominantly of silicatein, an enzyme that catalyzes the synthesis of biosilica. By differential display of transcripts we identified additional proteins involved in silica formation. Two genes were isolated from the marine demosponge Suberites domuncula; one codes for a galectin and the other for a fibrillar collagen. The galectin forms aggregates to which silicatein molecules bind. The extent of the silicatein-mediated silica formation strongly increased if associated with the galectin. By applying a new and mild extraction procedure that avoids hydrogen fluoride treatment, native axial filaments were extracted from spicules of S. domuncula. These filaments contained, in addition to silicatein, the galectin and a few other proteins. Immunogold electron microscopic studies underscored the role of these additional proteins, in particular that of galectin, in spiculogenesis. Galectin, in addition to silicatein, presumably forms in the axial canal as well as on the surface of the spicules an organized net-like matrix. In the extraspicular space most of these complexes are arranged concentrically around the spicules. Taken together, these additional proteins, working together with silicatein, may also be relevant for potential (nano)-biotechnological applications of silicatein in the formation of surface coatings. Finally, we propose a scheme that outlines the matrix (galectin/silicatein)-guided appositional growth of spicules through centripetal and centrifugal synthesis and deposition of biosilica.The members of the phylum Porifera (sponges) are grouped according to their mineral skeleton into three classes: Hexactinellida and Demospongiae, which comprise a siliceous skeleton, and Calcarea, with calcareous skeletal materials (1). The elements constituting these skeletons are termed spicules; they are used as systematic characters for a given sponge species (2). Given the comprehensive studies of Bütschli (3) and Minchin (4), a descriptive view of the formation of the siliceous spicules has been well established. In demosponges, where most studies have been performed with Suberites domuncula, spicules are initially formed within specialized cells called sclerocytes (5). S. domuncula has the advantage of containing only macroscleres (tylostyles/oxeas), whereas most other sponges, e.g. Tethya aurantium, contain macroscleres (oxeas) as well as microscleres (spherasters) (6). Spicules have in their center a 1-2-m-wide axial canal (7), which contains the axial filament. In demosponges first siliceous deposits are arranged around this axial filament. When spicules reach lengths of about 10 m they are extruded from the cells. The spicules are completed extracellularly in the mesohyl (8), where they reach final sizes of 10 m (microscleres) and 200 m (mac...

Demosponge and Sea Anemone Fibrillar Collagen Diversity Reveals the Early Emergence of A/C Clades and the Maintenance of the Modular Structure of Type V/XI Collagens from Sponge to Human

“…Moreover, Blast analyses of sponge or Hydra ESTs suggest the presence of B clade collagens in these taxa (9,20). Fibrillar collagen chains of undetermined clade have also been characterized in the freshwater demosponge Ephydatia mülleri (21) and in the marine demosponge Suberites domuncula (22).…”

Analysis of silicatein gene expression and spicule formation in the demosponge Amphimedon queenslandica

“…Indeed, silicatein also controls spicule growth, which occurs in two different directions, an increase in length due to the elongation of the axial filament, and an increased in width by apposition of silica lamellae Schröder et al 2006;Wang et al 2010). Silicatein may therefore be used for growth rather than for the formation of new spicules when a certain stage is reached, such as the larval stage, resulting in an unrelated expression with numbers.…”

“…Additional to water temperature, different concentrations of silica, iron, selenium and germanium can influence spicule formation (Krasko et al 2002;Le Pennec et al 2003;Müller et al 2005b;Simpson et al 1985). Silica concentration in the surrounding water and water temperature can affect silicatein gene expression, thus affecting spicule production (Krasko et al 2002;Schröder et al 2006). Data obtained in this study, specifically for larvae and postlarvae, were based in the laboratory where water quality differs from the natural condition.…”

“…These vesicles are present within the axial canal as well as around the spicule in the mesohyl (Müller et al 2005a;Schröder et al 2006;Wang et al 2011a), leading to axial and radial growth of the spicule. The axial growth corresponds to the deposition of silica lamellae on the inner surface of the spicule within the axial canal (Wang et al 2011a) (Fig.…”

“…Radial growth corresponds to the deposition of silica lamellae from the mesohyl onto the surface of the spicule. Silicatein appears to bind with galectin molecule in the presence of Ca 2+ and silintaphin-2 proteins to form a lamellar structure orientated by collagen around the growing spicule (Müller et al 2005a;Schröder et al 2006;Wang et al 2010;Wiens et al 2011). A mature spicule is formed when the apposition of those lamellae fuse to form a solid siliceous layer around the filament ).…”