MOLECULAR-CLONING AND CDNA SEQUENCE-ANALYSIS OF COHO SALMON STANNIOCALCIN

Stanniocalcin (STC) (formerly known as both teleocalcin and hypocalcin) is an anti-hypercalcemic, glycoprotein hormone that is produced by the corpuscles of Stannius (CS), endocrine glands that are confined to bony fishes. The hormone has a unique amino acid sequence and exists as a disulfide-linked homodimer in the native state. In previous studies, we have described the purification and characterization of two salmon STCs, and examined the regulation of hormone secretion in response to calcium using both in vitro and in vivo model systems. This report describes the molecular cloning and cDNA sequence analysis of a coho salmon STC messenger RNA (mRNA) from a salmon CS lambda gt10 cDNA library. The STC mRNA in salmon is approximately 2 kilobases in length and encodes a primary translation product of 256 amino acids. The first 33 residues comprise the prepro region of the hormone, whereas the remaining 223 residues make up the mature form of the hormone. One N-linked, glycosylation consensus sequence was identified in the protein coding region as well as an odd number of half cysteine residues, the latter of which would allow for interchain bonding or dimerization of monomeric subunits. In addition, three sites were identified in the mature protein core of STC (two dibasic, one tribasic) that may be acted upon by endopeptidases to produce truncated forms of the hormone. In support of this latter possibility, Western blot analysis revealed multiple molecular weight forms of STC within salmon glands.