0023-6152

AA00697606

1800841

Unrefereed

0023-6152

AA00697606

Stanniocalcin (STC) is a glycoprotein hormone that was first isolated from teleost corpuscles of Stannius. STC is involved in the decrease in plasma Ca^2+ level in teleosts. Comparative studies between invertebrate chordate STC and two paralogous vertebrate STCs suggest that the chordate ancestral gene of STC diverged into two paralogous genes in the evolution of vertebrates. However, this evolutionary scenario remains unclear. To clarify the diversification process of vertebrate STC, we made an attempt to isolate orthologs of STC in extant jawless fishes (cyclostomes) located most distantly in the vertebrate tree of life. In the present study, we searched the STC–like sequence by performing degenerate PCR in the inshore hagfish Eptatretus burgeri. We identified a STC homolog, designated as Eb–STC. Our molecular phylogenetic analysis confirmed that Eb–STC is a member of the STC family. The comparison of amino acid sequences revealed that Eb–STC is similar to gnathostome STC1 and 2, in that Eb–STC shares the 10 conserved cysteine residues that form intramolecular disulfide bonds. Eb–STC and gnathostome STCs possess the conserved N–glycosylated site. However, typical features discriminated between STC1 and 2, such as the distinct position of the cysteine residue associated with the intermolecular dimer, were not observed in Eb–STC. Tissue distribution analysis revealed that Eb–STC is expressed in various organs, but not in the brain. This expression pattern resembles that of teleost STC1 and 2, suggesting that Eb–STC acts as a paracrine factor. To the best of our knowledge, this is the first report on the identification and molecular characterization of STC in cyclostomes.