
<ArticleTitle>The ABC transporter <prot>Bcrp1</prot>/<prot>ABCG2</prot> is expressed in a wide variety of stem cells and is a molecular determinant of the side-population phenotype.</ArticleTitle>
<AbstractText>Stem cells from bone marrow, skeletal muscle and possibly other tissues can be identified by the 'side-population' (SP) phenotype. Although it has been assumed that expression of ABC transporters is responsible for this phenotype, the specific molecules involved have not been defined. Here we show that expression of the <prot>Bcrp1</prot> (also known as <prot>Abcg2</prot> murine/<prot>ABCG2</prot> human) gene is a conserved feature of stem cells from a wide variety of sources. <prot>Bcrp1</prot> mRNA was expressed at high levels in primitive murine hematopoietic stem cells, and was sharply downregulated with differentiation. Enforced expression of the <prot>ABCG2</prot> cDNA directly conferred the SP phenotype to bone-marrow cells and caused a reduction in maturing progeny both in vitro and in transplantation-based assays. These results show that expression of the <prot>Bcrp1</prot>/<prot>ABCG2</prot> gene is an important determinant of the SP phenotype, and that it might serve as a marker for stem cells from various sources.</AbstractText>
