Animal-based reporter assays using reporter mice are a potentially powerful tool for the identification of drug candidates. To our knowledge, the ERE-Luc (estrogen responsive element-luciferase gene) mouse is the first example of a reporter animal to be used for drug development [25] , although several studies with simple reporter mice have been documented previously [26] [27] [28] . The ERE-Luc model is a unique reporter animal for drug discovery that was developed to identify ligands that bind estrogen receptors (ERs). Because ERs are ubiquitously expressed in mammals, this mouse model was required to be generally applicable to the activity of ERs [29] .