Müller Werner E G, Krasko Anatoli, Le Pennec Gaël, Schröder Heinz C
Institut für Physiologische Chemie, Abteilung Angewandte Molekularbiologie, Universität, D-55099 Mainz, Germany.
Microsc Res Tech. 2003 Nov 1;62(4):368-77. doi: 10.1002/jemt.10402.
The main inorganic material forming the skeletal elements in Demospongiae as well as in Hexactinellida, the spicules, is amorphous silica. The spicules occur in the cytoplasm and the extracellular space and also in the nucleus (as silicate crystals) of some sponge cells; the function in the latter compartment is unknown. Recent evidence shows that the formation of spicules is mediated by the enzyme silicatein. The cDNA as well as the gene encoding this enzyme was cloned from Suberites domuncula. The recombinant silicatein catalyzes the synthesis of amorphous silicate using tetraethoxysilane as substrate. The enzyme is dependent on ferric iron. Silicatein also has proteolytic (cathepsin-like) activity. Incubation of primmorphs, a special form of 3D-cell aggregates, with silicon resulted in a strong increase of their size from 1-7 mm to approximately 10 mm. The morphogenetic activity of silicate is underscored by the finding that this ion increases gene expression of silicatein and collagen. Based on these findings, it is concluded that both iron and silicate stimulate the activity of silicatein. Furthermore, it is proposed that the growing spicules are surrounded by the scavenger receptor which might be considered as a docking molecule for the collagen matrix into which the spicules are embedded.
在寻常海绵纲以及六放海绵纲中，构成骨骼成分的主要无机物质——骨针，是无定形二氧化硅。骨针存在于细胞质、细胞外空间，在某些海绵细胞的细胞核中也有（呈硅酸盐晶体形式）；其在细胞核中的功能尚不清楚。最近的证据表明，骨针的形成由硅酸酶介导。编码这种酶的cDNA以及基因已从多孔动物软海绵中克隆出来。重组硅酸酶以四乙氧基硅烷为底物催化无定形硅酸盐的合成。该酶依赖于三价铁。硅酸酶还具有蛋白水解（类组织蛋白酶）活性。用硅处理原形体（一种特殊形式的三维细胞聚集体），其大小会从1 - 7毫米显著增加到约10毫米。硅酸增加硅酸酶和胶原蛋白的基因表达这一发现突出了硅酸的形态发生活性。基于这些发现，可以得出铁和硅酸都能刺激硅酸酶活性的结论。此外，有人提出生长中的骨针被清道夫受体包围，该受体可被视为骨针所嵌入的胶原蛋白基质的对接分子。
