Isolation of Growth Hormone-Releasing Hormone and Its Receptor Genes from Scatophagus argus and Their Expression Analyses

The teleost Scatophagus argus is a species whose females grows faster than males. Growth hormone ( gh ) mRNA abundance in females pituitary is higher than that in males; however the mechanism underlining such differential is still unknown. Growth hormone (GH) is tightly associated with GH-releasing hormone (Ghrh) in vertebrates. In this study, Ghrh gene ( ghrh ) and its receptor gene, ghrhr , were isolated from S. argus . Tissue expression analysis showed that ghrh and ghrhr were mainly expressed in hypothalamus while ghrhr was expressed in pituitary and gh was predominantly expressed in pituitary. Twenty cultured S. argus individuals were used to compare ghrh, ghrhr and gh mRNA abundances, 120 g and 181 g average weight for male ( n =11) and female ( n = 9), respectively. Real-time PCR indicated that the ghrh and ghrhr mRNA abundances in male hypothalamus were significantly higher than those in female hypothalamus while that of gh mRNA abundance was significantly higher in female pituitary than in male pituitary. The ghrh and ghrhr mRNA abundances were significantly up-regulated in female hypothalamus 3h after injection of 0.1 mg kg −1 body weight Ghrh while pituitary ghrhr and gh mRNA abundances were not affected. In female hypothalamus, ghrh and ghrhr mRNA abundances were not affected at 6h post-injection of 4mg kg −1 body weight 17α-methyltes-tosterone (17α-MT) or 17β-Estradiol (E 2 ). In female pituitary, ghrhr mRNA abundance was down-regulated by 17α-MT while that of gh mRNA abundance was up-regulated by E 2 . Our findings indicated that E 2 , rather than Ghrh, plays an important role in up-regulating the expression of gh in female S. argus , which should aid to understand the sexual dimorphism of teleost growth.