The ATP-binding cassette (ABC) transporter 2 (ABCG2) is expressed by stein cells in many organs and in stein cells of solid tumors. These cells are isolated based on the side population (SP) phenotype, a Hoechst 3342 dye efflux property believed to be conferred by ABCG2. Because of the limitations of this approach we generated transgenic mice that express Nuclear GFP (GFPn) Coupled to the Puromycin-resistance gene, under the control of ABCG2 promoter/enhancer sequences. We show that ABCG2 is expressed in neural progenitors of the developing forebrain and spinal cord and in embryonic and adult endothelial cells of the brain. Using the neurosphere assay, we isolated tripotent ABCG2-expressing neural stein cells from embryonic mouse brain, This transgenic line is a powerful tool for studying the expression of ABCG2 in many tissues and for performing functional studies in different experimental settings. (C) 2009 Elsevier Inc. All rights reserved.