KAILASANATH, V.; BURMEISTER, S.S.; HOKE, K.L.; FERNALD, R.D.; Stanford University; Stanford University; Stanford University; Stanford University: Characterization of Multiple Estrogen Receptors in a Cichlid Fish
Estrogen plays a critical role in development, physiology, and behavior of both males and females through its action on estrogen receptors (ERs). In the cichlid fish, Haplochromis burtoni, social behaviors are important regulators of steroid hormones and steroids, in turn, influence behavior. To understand how steroids are integrated with social cues, we are characterizing the ERs in the brain of H. burtoni. Phylogenetic analysis indicates the existence of three forms of ER (ER-&alpha, -&beta 1, and -&beta 2) in teleosts due to an early duplication of ER-&beta during evolution. We cloned partial sequences of two forms of ER using degenerate PCR coupled with rapid amplification of cDNA ends. Based on sequence similarity and phylogenetic analysis, our 3 kb clone (containing D and E/F domains and 3� untranslated region (UTR)) is ER-&alpha and our 1.4 kb clone (containing 5� UTR, A/B and C domains) is an ER-&beta. The predicted amino acid sequence of our ER-&alpha clone is 54% identical to human ER-&alpha and 63% to zebrafish ER-&alpha. The predicted amino acid sequence of our ER-&beta clone shares 64, 61, and 69% sequence identity to human ER-&beta, zebrafish ER-&beta 1, and zebrafish ER-&beta 2, respectively. Based on a comparison with ER forms in species for which three ERs have been cloned, we concluded that our ER-&beta fragment was most similar to the third form of ER first described in Atlantic croaker as ER-&gamma and subsequently called ER-&beta 2 in zebrafish. We also localized expression of H. burtoni ER-&alpha and -&beta in male and female brains using in situ hybridization. Both forms of ER were expressed in the preoptic area (POA), although distribution of the two genes differed, as ER-&beta was also expressed in the ventral part of the subpallium. This distribution pattern shows estrogen may affect brain regions known to control reproductive and social behaviors.
