Abstract:In order to deeply understand underlying mechanisms for regulating reproductive trait of Cynoglossus semilaevis, the physiological role of GH/IGF-Ⅰaxis in ovarian development was explored. The levels of growth hormone (GH) mRNA of pituitary and IGF-Ⅰ mRNA of liver, brain, and ovary at different ovarian development stages were determined by quantitative real-time PCR (qRT-PCR) analysis. Meanwhile, the expression levels of serum GH, IGF-Ⅰ, estradiol (E2) and testosterone (T) were detected by radioimmunoassay (RIA) and ELISA methods, respectively. Furthermore, the correlation between the mRNA and peptides expression levels of GH, IGF-Ⅰand gonadosomatic index (GSI), and the one between the expression levels of serum E2 and serum T during ovarian development was calculated with statistical methods. The results showed that, the levels of pituitary GH mRNA significantly increased at stage Ⅳ ovary, and peaked at stage Ⅴ ovary, but decreased significantly post spawning (stage Ⅵ). It has significantly positive relationship with the expression levels of GSI, serum GH and serum IGF-Ⅰ during ovarian development. The serum GH levels showed similar trend with pituitary GH mRNA expression levels. Liver IGF-Ⅰ mRNA achieved the minimum levels at stage Ⅳ and stage Ⅴ ovaries, but with a significant increase at stage Ⅵ ovary. It was significantly positive correlated with brain IGF-Ⅰ mRNA levels and serum IGF-Ⅰ levels, but significantly negative correlated with serum E2 and serum T levels during ovarian development. Brain IGF-Ⅰ mRNA levels significantly increased since stage Ⅱ ovary and peaked at stage Ⅳ ovary, and showed a significant negative relationship with serum IGF-Ⅰ levels. Ovary IGF-Ⅰ mRNA levels significantly increased at stage Ⅱ ovary and peaked at stage Ⅳ ovary, then significantly declined at stage Ⅴ ovary until stage Ⅵ ovary. It was significantly correlated with serum E2 levels but negatively correlated with serum IGF-Ⅰlevels. Serum IGF-Ⅰ levels showed similar trend with liver IGF-Ⅰ mRNA levels, which significantly decreased at stage Ⅳ ovary, but then significantly ascended to peak at stage Ⅵ ovary. These results revealed that GH and IGF-Ⅰ synergistically or antagonistically play physiological role in ovarian development of C. semilaevis in endocrine or paracrine ways, and their regulation functions are related with synthesis/secretion during ovary development regulation. The present results could provide a new clue for better understanding the possible mechanism for reproductive regulation of C. semilaevis.
