Expression and cellular localization of somatostatin fromParalichthys olivaceus

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Somatostatin(SS) called also somatotropin release-inhibiting factor is a peptide named for its ability to inhibit pituitary growth hormone release.To facilitate investigation of the SS function in the teleost,its coding sequence in paralichthys olivaceus was isolated by the technique of Rapid Amplification of cDNA Ends(RACE).SYBR Green I Quantitative Real-time PCR analysis and immunohistochemistry were used to assess the expression of SS at mRNA and protein level.The deduced protein sequence con-tains 126 amino acid residues and a predicted molecular mass of 14.3 kD.Very low level of SS mRNA is presented during the first three days after hatching.The expression level of the SS gene was increased con-stantly before metamorphosis and steadily during the metamorphosis,then increased significantly during post-metamorphosis.There was no SS-positive reaction in the oropharyngeal cavity and esophagus.SS secreting cells are only distributed in the stomach,pancreas and pituitary.Several types of SS secreting cells could be distinguished in above organs.In stomach,SS secreting cells are dispersively distributed among the epithelium cells,presenting various kinds of forms such as ovoid,globular,triangle,elongated or spindle-shaped aspects.The pancreas and liver of flounder combine into a single organ named hepato-pancreas,and SS-positive cells are only located in the pancreas,showing as globular-shaped,most of them are closed to blood vessels.SS-positive cells at high density are located in pars distalis of pituitary,so it is difficult to distinguish the shape of those cells.