Molecular Characterization of a Nonfibrillar Collagen from the Marine Sponge <Emphasis Type="Italic">Chondrosia reniformis</Emphasis> Nardo 1847 and Positive Effects of Soluble Silicates on Its Expression

We report here the complete cDNA sequence of a nonfibrillar collagen (COLch) isolated from the marine sponge Chondrosia reniformis, Nardo 1847 using a PCR approach. COLch cDNA consists of 2,563 nucleotides and includes a 5′ untranslated region (UTR) of 136 nucleotides, a 3′ UTR of 198 nucleotides, and an open reading frame encoding for a protein of 743 amino acids with an estimated M _r of 72.12 kDa. The phylogenetic analysis on the deduced amino acid sequence of C-terminal end shows that the isolated sequence belongs to the short-chain spongin-like collagen subfamily, a nonfibrillar group of invertebrate collagens similar to type IV collagen. In situ hybridization analysis shows higher expression of COLch mRNA in the cortical part than in the inner part of the sponge. Therefore, COLch seems to be involved in the formation of C. reniformis ectosome, where it could play a key role in the attachment to the rocky substrata and in the selective sediment incorporation typical of these organisms. qPCR analysis of COLch mRNA level, performed on C. reniformis tissue culture models (fragmorphs), also demonstrates that this matrix protein is directly involved in sponge healing processes and that soluble silicates positively regulate its expression. These findings confirm the essential role of silicon in the fibrogenesis process also in lower invertebrates, and they should give a tool for a sustainable production of marine collagen in sponge mariculture.