Molecular cloning, characterization, and mRNA expression of gonadotropins during larval development in turbot (Scophthalmus maximus)

摘要

Gonadotropins (GtHs) play a pivotal role in regulating the reproductive axis and puberty. In this study, full-length sequences coding for common glycoprotein alpha subunit (CG alpha) and luteinizing hormone beta (LH beta) were isolated from female turbot (Scophthalmus maximus) pituitary by homology cloning and a strategy based on rapid amplification of cDNA end-polymerase chain reaction. Results showed that the two cDNAs consisted of 669 and 660 nucleotides encoding 129 and 139 amino acids, respectively. CG alpha and LH beta manifested typical characteristics of glycoprotein hormones, high homologies with the corresponding sequences of available teleosts, and high homology with that of Hippoglossus hippoglossus. CG alpha, FSH beta, and LH beta mRNAs were abundant in the pituitary, but less expressed in extra-pituitary tissues. The cg alpha, fsh beta, and lh beta were detected at 1-day post-hatching (dph) and peaked simultaneously at early-metamorphosis (22 dph). cg alpha and fsh beta mRNA levels were significantly increased at pre-metamorphosis, peaked in early metamorphosis, and then gradually decreased until metamorphosis was completed. Conversely, lh beta mRNA levels gradually decreased at pre-metamorphosis, dramatically peaked at early metamorphosis, and then decreased during metamorphosis. In addition, the mRNA levels of cg alpha were significantly higher than those of fsh beta and lh beta during turbot larval metamorphic development, whereas no significant difference was found between fsh beta and lh beta. These results suggested (i) an early activation of the GtHs system after hatching, which was the highest expression at early metamorphosis, and (ii) FSH beta and LH beta were together involved in the establishment of the reproductive axis during larval development in turbot. These findings contribute to further understanding the potential roles of GtHs during fish larval development.