Novel expression of the stanniocalcin gene in fish

It is currently accepted that the fish stanniocalcin (STC) gene is expresse d exclusively in the corpuscles of Stannius (CS), unique endocrine glands o n the kidneys of bony fishes. In this study, we have re-examined the patter n of fish STC gene expression in the light of the recent evidence for wides pread expression of the gene in mammals. Surprisingly, we found by Northern blotting that the fish gene was also expressed in the kidneys and gonads, in addition to the CS glands. Moreover, Southern blotting of PT-PCR product s revealed STC mRNA transcripts in all tissues assayed, including brain, he art, gill, muscle and intestine. In situ hybridization Studies using digoxi genin-labeled riboprobes localized STC mRNA to chondrocytes, and both matur e and developing nephritic tubules. Immunocytochemical staining indicated t hat the STC protein was widespread in cells of the gill, kidney, brain, eye . pseudobranch and skin. We also characterized the salmon STC gene, establi shing that it vas comprised of five exons as opposed to four in mammals. A single transcription start site was identified by printer extension 99 bp u pstream of the start codon. This is the first evidence of STC gene expressi on in fish tissues other than the CS glands and suggests that, as in mammal s, fish STC operates via both local and endocrine pathways.