cDNA cloning of Japanese flounder stanniocalcin 2 and its mRNA expression in a variety of tissues.

Stanniocalcin 1 (STC1) is a glycoprotein hormone important in the maintenance of calcium and phosphate homeostasis in both fishes and mammals. Although two related STC genes, STC1 and STC2, were found to be expressed in multiple tissues as paracrine regulators in mammals, spatial expression pattern of stc2 mRNA has not been elucidated in fishes in contrast to that of clearly described stc1. In the present study, we have cloned and characterized a full-length stc2 cDNA from Japanese flounder (Paralichyhus olivaceus) ovary and analyzed expression pattern of stc2 in both sexes. The flounder stc2 cDNA (1501 nucleotides) encoded a putative prehormone of 286 amino acids (aa) with a signal peptide of 20 aa and a mature protein of 266 aa. The deduced aa sequence of flounder stc2 showed high sequence identity with those of pufferfish, zebrafish, and human (57.7-89.0%), whereas it showed less identity with that of flounder stc1 (24.3%). RT-PCR analysis revealed that the flounder stc2 gene is expressed in all examined tissues including the pituitary, brain, heart, kidney, gills, stomach, spleen, skin, dorsal fin, skeletal muscle, liver, corpuscles of Stannius, intestine, ovary and testis. Our data indicate that fish stc2 gene, like stc1, is expressed in a wide variety of tissues.