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.