Molecular cloning of estrogen receptors alpha and beta in the ovary of a teleost fish, the Tilapia (Oreochromis niloticus)

Estrogen receptors (ER) in mammals have recently been shown to be encoded b y two distinct genes, ER alpha and ER beta. In this study, cDNAs encoding t wo tilapia ER subtypes, tER5.1 and tER4.3, were cloned from an ovarian cDNA library of a teleost fish, the tilapia Oreochromis niloticus. The tER5.1 a nd tER4.3 contain complete open reading frames encoding 585 and 557 amino a cid residues, respectively. The two receptors share about 12% homology in t he A/B domain, 96% in the DNA binding domain (C domain), 12% in the D domai n, 57% in the ligand binding domain (E damain), and 20% in the F domain. Ph ylogenetic analysis of ER proteins from various vertebrate species indicate d that vertebrate ERs consist of two major groups (ER alpha and ER beta); t ER5.1 and tER4.3 belong to ER alpha and ER beta subtypes, respectively. Thu s, we consider tER5.1 and tER4.3 to be the tilapia homologs of ER alpha (tE R alpha) and ER beta (tER beta), respectively. In transient transfection as says using mammalian COS-7 cells, both tER alpha and tER beta showed estrad iol-17 beta dependent activation of transcription from the estrogen-respons ive ERE-Luc promoter. This is the first report of the presence of ER alpha and ER beta within a single non-mammalian vertebrate species.