Studies of the function and gene of somatolactin, a new pituitary hormone

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The goal of the roject is to stablish a newy fund pituitary protein, somatolactin, as a tropic hormone. Somatolactin (SL) is a new hypophysial member of growth hormone (GH) and prolactin (PRL) family of teleosts. SLs of Atantic cod, flunder, salmonids, gilthead, carp, and channel catfsh, and SLcDNAs of flunder, Atantic cod, and chum salmon have been identified. Comparison of the SL sequences so far analyzed indicates that this protein is highly conserved, more so than the GHs from the corresponding species. Immunhistochemistry with a specific antiserum to cod SL revealed that SL is present in periodic-acid-Shiff-positive cells of the ars intermeda in cod and mst other teleost species, and in chromophoic cells of the pars intermedia in salmonids. By an eectron-microscopic immunohistochemistry protein A-gold complex s localized mostly on the secretory granules of these cels of rainbow trout. A homologous radio-immunoassay specific for salmon SL was deeloped and validated. Increases of plasma SL levels have been bserved, during the final year of reroductive maturation of coho slmn, after transfer rainbow trout from Ca-rich fresh water to fresh water, and after exposure rainbow trout to acidic waer. These findings suggest that SL regulates reproduction, Ca-metabolism, and acid-base balance. Salmon SL gene was comprised of five exones as in the case of mammalian GH/PRL gees, but was ulike salmnid GH genes, which have 6 exones. Upstream from the transcriptional initiation site were found one TATA box and four consensus sequences corresponding to the Pit-1 binding element, which is known to be essential to expression of mammalian GH and PRL genes. Salmon Pit-1 mRNA was found to encode a 365 amino acid protein, which was 74 residues larger than that of rat Pit-1. Using antibody against chum samon Pit-1, this protein was shwn to be located in the nuclei in the SL-producing cells in the pars intermedia. In experments of cotransection into HeLa cells, Pit-1 enhanced the promo