Nucleotide sequence, tissue expression patterns and phylogenetic analysis of estrogen receptor one mRNA in the Murray rainbowfish (Melanotaenia fluviatilis) (Atheriniformes, Actinopterygii)

Estrogens are steroidal hormones that control many physiological processes in both female and male vertebrates. Like other vertebrates, fish have two distinct estrogen receptors (Esr) subtypes, Esr1 and Esr2a that have been isolated in a number of species, as well as a third subtype, Esr2b. The mRNA encoding the Esr1 was isolated from the female liver of an Australian freshwater fish, the Murray rainbowfish, Melanotaenia fluviatilis. The rainbowfish esr1 cDNA was 2569 bp in length and with an open reading frame to encode a protein of 611 amino acids. Phylogenetic analysis and multiple amino acid sequence alignment indicated close relationship and high similarity with killifish (Fundulus heteroclitus) and gilthead sea bream (Sparus aurata). Expression of rainbowfish esr1 mRNA was abundant in the liver, gonads and intestine of adult female and male rainbowfish. This is the first isolation of the full-length nucleotide sequence of an estrogen receptor from rainbowfish. This sequence provides a valuable molecular tool that can be used in future studies investigating estrogen mechanisms, actions and tissue-specific expression in juvenile and adult rainbowfish.