Abstract:
Steroid hormones are a key regulator of reproductive biology in vertebrates, and are largely
regulated via nuclear receptor families. Estrogen signaling is regulated by two estrogen
receptor (ER) subtypes alpha and beta in the nucleus. In order to understand the role of
estrogen in vertebrates, these ER from various species have been isolated and were
functionally analyzed using luciferase reporter gene assays. Interestingly, species difference
in estrogen sensitivity has been noted in the past, and it was reported that snake ER displayed
highest estrogen sensitivity. Here, we isolated additional ER from three lizards: chameleon
(Bradypodion pumilum), skink (Plestiodon finitimus), and gecko (Gekko japonicus). We have
performed functional characterization of these ERs using reporter gene assay system, and
found high estrogen sensitivity in all three species. Furthermore, comparison with results 2
from other tetrapod ER revealed a seemingly uniform gradual pattern of ligand sensitivity
evolution. In silico 3D homology modeling of the ligand-binding domain revealed structural
variation at three sites, helix 2, and juncture between helices 8 and 9, and caudal region of
helix 10/11. Docking simulations indicated that predicted ligand-receptor interaction also correlated with the reporter assay results, and overall squamates displayed highest stabilized interactions. The assay system and homology modeling system provides tool for in-depth comparative analysis of estrogen function, and provides insight toward the evolution of ER among vertebrates.
