Tissue-based stem cells: ABC transporter proteins take centre stage

Abstract

In adult tissues, with the notable exception of the haematopoietic system, the identity of somatic stem cells has often been inferred based on no more evidence than their location. Functional data (clonogenicity) to confirm such an appellation has been absent due to the inability to find appropriate cellular markers with which to isolate live stem cells. Flow cytometry has isolated haematopoietic stem cells based on their ability to exclude Hoechst dye. Named the side population (SP), this phenotype may be a universal marker of stem cells in adult tissues.