Molecular cloning of estrogen receptor alpha and expression pattern of estrogen receptor subtypes in male and female goldfish.

Estrogen plays an important role in the regulation of gonadotropin production in vertebrates. In this study, we isolated the estrogen receptor (ER) alpha cDNA from the goldfish pituitary. Primers for ERalpha were designed based on the similarity of selected regions (C and E domains) of known ER genes. Full-length cDNA sequence for ERalpha was determined by 3' and 5' RACE procedures. ERalpha cDNA clone was found to contain 2087 nucleotides including an open reading frame that encodes 564 amino acids, with a molecular weight of 62.8 kDa. We also cloned ERbeta-1 and ERbeta-2 from the published information and investigated the expression pattern of these ER subtypes in a variety of tissues in male and female goldfish by reverse transcriptase-polymerase chain reaction (RT-PCR). Significant variations in the relative expression of ERalpha, ERbeta-1 and ERbeta-2 were observed in different tissues in male and female goldfish. Pituitary was found to have the highest expression level of ERalpha in both male and female goldfish. Significantly, lower levels of ERalpha expression were observed in the brain, ovary, testis, liver, muscle, heart and intestine. Ovary and testis were found to have higher transcript levels of ERbeta-1 with much lower levels in the brain, pituitary, liver, muscle and heart. The ERbeta-2 was found to be expressed strongly in the pituitary followed by intestine with lower expression in other tissues. The present study provides molecular characterization of ERalpha, and information on tissue specific distribution of different ER subtypes in male and female goldfish.