Expression of silicatein and collagen genes in the marine sponge Suberitesdomuncula is controlled by silicate and myotrophin

The major skeletal elements in the (Porifera) sponges, are spicules formed from inorganic material. The spicules in the Demospongiae class are compose d of hydrated, amorphous silica. Recently an enzyme, silicatein, which poly merizes alkoxide substrates to silica was described from the sponge Tethya aurantia. In the present study the cDNA encoding silicatein was isolated fr om the sponge Suberites domuncula. The deduced polypeptide comprises 331 am ino acids and has a calculated size of M-r 36 306. This cDNA was used as a probe to study the potential role of silicate on the expression of the sili catein gene. For these studies, primmorphs, a special form of aggregates co mposed of proliferating cells, have been used. It was found that after incr easing the concentration of soluble silicate in the seawater medium from ar ound 1 mu m to approximately 60 mu m, this gene is strongly upregulated. Wi thout additional silicate only a very weak expression could be measured. Be cause silica as well as collagen are required for the formation of spicules , the expression of the gene encoding collagen was measured in parallel. It was also found that the level of transcripts for collagen strongly increas es in the presence of 60 mu m soluble silicate. In addition, it is demonstr ated that the expression of collagen is also upregulated in those primmorph s which were treated with recombinant myotrophin obtained from the same spo nge. Myotrophin, however, had no effect on the expression of silicatein. Fr om these data we conclude that silicate influences the expression of the en zyme silicatein and also the expression of collagen, (via the mediator myot rophin).