The estrogen plays critical roles in reproductive physiology through estrogen receptor(ER).The ERs are considered Class I members of the superfamily of nuclear receptors,characterized as ligand-inducible transcription factors.ER exists in two known forms,the classical estrog receptor-alpha(ERα) and the more recently discovered estrogen receptor-beta(ERβ).Gene targeting techniques were used to generate mice lacking either functional ERα(ERαKO),ERβ(ERβKO),or both ERs(ER αβ KO) to provide a model for evaluatin...