cDNA cloning and isolation of somatolactin in Mozambique tilapia and effects of seawater acclimation, confinement stress, and fasting on its pituitary expression.
Somatolactin (SL) is a member of the growth hormone (GH)/prolactin (PRL) family of pituitary hormones, and is found in a variety of teleost species. Somatolactin is thought to be involved in a wide range of physiological actions, including reproduction, stress response, the regulation of Ca(2+) and acid-base balance, growth, metabolism, and immune response. We report here on the cDNA structure of SL from the pituitary of Mozambique tilapia, Oreochromis mossambicus, and its gene expression in response to seawater acclimation, stress, and fasting. Tilapia SL cDNA (1573bp long) encoded a prehormone of 230 amino acids. Sequence analysis of purified SL revealed that the prehormone is composed of a signal peptide of 23 amino acids and a mature protein of 207 amino acids, which has a possible N-glycosylation site at position 121 and seven Cys residues. Tilapia SL shows over 80% amino acid identity with SLalpha of advanced teleosts such as medaka and flounder, and around 50% identity with SLbeta of carp and goldfish. Acclimation to seawater had no effect on pituitary expression of SL or on hepatic expression of the putative tilapia SL receptor (GHR1). By contrast, seawater acclimation resulted in significant increases in pituitary GH expression and in hepatic expression of tilapia GH receptor (GHR2). Confinement stress had no effect on pituitary expression of either SL or GH, or on hepatic expression of GHR1, whereas a significant increase was seen in GHR2 expression in the liver. Fasting for 4 weeks resulted in significant reductions in SL transcripts both in fresh water and seawater. It is highly likely that SL is involved in metabolic processes in tilapia along with the GH/IGF-I axis.
Uchida
Katsuhisa
K
Sado Marine Biological Station, Niigata University, Sado, Niigata, Japan. k-uchida@cc.niigata-u.ac.jp
Moriyama
Shunsuke
S
Breves
Jason P
JP
Fox
Bradley K
BK
Pierce
Andrew L
AL
Borski
Russell J
RJ
Hirano
Tetsuya
T
Grau
E Gordon
EG
D000064:Acclimatization / Q000502:physiology; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular / Q000379:methods; D018076:DNA, Complementary / Q000235:genetics; D005215:Fasting / Q000502:physiology*; D029941:Fish Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D005786:Gene Expression Regulation; D006023:Glycoproteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013006:Growth Hormone / Q000235:genetics; D008969:Molecular Sequence Data; D010902:Pituitary Gland / Q000378:metabolism*; D010907:Pituitary Hormones / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D016133:Polymerase Chain Reaction; D011986:Receptors, Somatotropin / Q000235:genetics; D012623:Seawater; D016415:Sequence Alignment; D013312:Stress, Physiological / Q000502:physiology*; D017210:Tilapia / Q000235:genetics / Q000378:metabolism
D018076:DNA, Complementary; D029941:Fish Proteins; D006023:Glycoproteins; D010907:Pituitary Hormones; D011986:Receptors, Somatotropin; C064448:somatolactin protein, fish; D013006:Growth Hormone