Regulatory roles of sterol regulatory element-binding protein (SREBP) on lipid metabolism in marine invertebrate Chlamys nobilis

Sterol regulatory element-binding protein (SREBP) has mainly been studied in vertebrates in which lipogenesis is regulated in both liver and adipose tissue. There is, however, a paucity of information on bivalves, in which lipogenesis occurs essentially in ovary. To investigate the regulatory roles of SREBP on lipid metabolism in mollusks, the cDNA of scallop Chlamys nobilis was sequenced, its expression in different tissues and different developmental ovary stages was studied, and effect of 17β-estradiol (E2) on CnSREBP in ovary was investigated. The predicted scallop SREBP contains a conserved helix-loop-helix domain and a leucine zipper (bHLH-Zip) region, however, the amino acid sequence only shows a 39-45% identity with vertebrate. Phylogenetic tree analysis showed that the putative scallop SREBP (CnSREBP) clustered separately with invertebrate SREBP-1 and SREBP-2. There is a significantly positive correlation between CnSREBP expression level and lipid content in tissues (r = 0.9705, P < 0.001), but a reverse relationship between the gene expression level and ovary mature degree. Moreover, the gene was significantly repressed by 17β-estradiol. Our results indicated that CnSREBP was similar with vertebrate SREBP-1, which could regulate lipid metabolism in the scallops.