Molecular characterization and quantification of estrogen receptors in turbot (Scophthalmus maximus)

Estrogens regulate various reproductive processes via estrogen receptor (ER)-mediated signaling pathway in vertebrates. In this study, full-length sequences coding for ER alpha, ER beta 1 and ER beta 2 were isolated from female turbot (Scophthalmus maximus) by homology cloning and a strategy based on rapid amplification of cDNA end-polymerase chain reaction (RACE-PCR). The nucleotide and amino acid sequences of turbot ERs showed high homologies with the corresponding sequences of other fish species and significant homology with the Japanese flounder (Paralichthys olivaceus) and the European sea bass (Dicentrarchus labrax). Turbot ERs contained six typical nuclear receptor-characteristic domains and exhibited high evolutionary conservation in the functional domains. Quantitative real-time polymerase chain reaction analysis revealed that the er alpha and er beta (beta 1, beta 2) mRNAs were abundant in the liver and ovary, respectively. Furthermore, hepatic mRNA levels of er alpha and vitellogenin (vtg) were found increased gradually from pre-vitellogenesis to late-vitellogenesis stages, with the highest values observed at the late-vitellogenesis stage, and then decreased from migratory-nucleus to atresia stages. However, mRNA levels of er alpha in the ovary remained unchanged during ovarian development. Hepatosomatic index, gonadosomatic index, serum estradio1-17 beta and the mRNA levels of er beta 1 and er beta 2 in the ovary manifested results similar to the expression of er alpha mRNAs in the liver. These findings indicated that ER alpha is mainly involved in hepatic vitellogenesis, and ER beta s may play crucial roles to regulate ovarian development in turbot. Overall, this study improves understanding of the physiological functions of turbot ERs, which will be valuable for fish reproduction and broodstock management. (C) 2017 Elsevier Inc. All rights reserved.