Toward understanding the morphogenesis of siliceous spicules in freshwater sponge: Differential mRNA expression of spicule‐type‐specific silicatein genes in Ephydatia fluviatilis

Abstract

Siliceous spicules of sponges are morphologically diverse and provide good models for understanding the morphogenesis of biomineralized products. The silica deposition enzyme silicatein is a component of siliceous spicules of sponges and is thought to be the key molecule determining the morphology of spicules. Here, we focused on the silicateins of the freshwater sponge Ephydatia fluviatilis, which has two types of morphologically and functionally different spicules, called megascleres and gemmoscleres. We isolated six isoforms of silicateins and examined their mRNA expression in the cells producing megascleres and gemmoscleres. The spicule-type-specific mRNA expression of these isoforms and differential expression during spicule development suggest that the characteristic morphology of spicules is due to the specific properties and combinatory functions of silicatein isoforms. Developmental Dynamics 237:3024 -3039, 2008.

Glassin, a histidine-rich protein from the siliceous skeletal system of the marine sponge Euplectella , directs silica polycondensation

“…Because these initial early discoveries, silicateins have been identified in numerous other demosponge species (12)(13)(14)(15)(16)(17)(18).…”

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

“…Afterward, silicatein has been isolated from other marine sponges, including Petrosia ficiformis (Pozzolini et al 2004), Hymeniacidon perlevis (Cao et al 2007), Cratomorpha meyeri (Müller et al 2008b), Latrunculia oparinae (Kozhemyako et al 2009) and Geodia cydonium (Müller et al 2007c), as well as freshwater sponges including Lubomirskia baicalensis (Kaluzhnaya et al 2005;Kaluzhnaya et al 2011), Ephydatia fluviatilis (Funayama et al 2005;Mohri et al 2008) and Ephydatia muelleri (Kaluzhnaya et al 2011). …”

“…However, freshwater sponges seem to lack silicatein β but often code for four isoforms of silicatein α (e.g. E. fluviatilis and L. baicalensis; Kaluzhnaya et al 2005;Kaluzhnaya et al 2011;Mohri et al 2008). In E. fluviatilis primmorph the different silicatein α isoforms are expressed at different times during the formation of spicules (Mohri et al 2008),…”

“…This is followed by an extracellular phase where spicule growth is driven by the concentration of soluble silica present in the surrounding environment. The final morphogenesis of spicules is poorly characterised (Chombard et al 1998;Mohri et al 2008;Uriz 2006). It has been suggested that the final shape of the spicule is driven by the shape of the filament (Ecker et al 2006;Piserra 2003).…”

“…Silicatein is present specifically in siliceous sponges (demonsponges, hexactinellids and homoscleromorphs) and was first discovered in the axial filament of the demosponge Tethya aurantia where two genes have been isolated, silicatein α and silicatein β (Shimizu et al 1998). Silicatein genes have since been identified in other marine and freshwater sponges (Krasko et al 2000;Pozzolini et al 2004;Cao et al 2007;Kaluzhnaya et al 2005;Funayama et al 2005;Mohri et al 2008).…”