Open AccessA Side Order of Stem Cells: The SP Phenotype
Author(s) -
Challen Grant A.,
Little Melissa H.
Publication year - 2006
Publication title -
stem cells
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.159
H-Index - 229
eISSN - 1549-4918
pISSN - 1066-5099
DOI - 10.1634/stemcells.2005-0116
Subject(s) - stem cell , biology , side population , microbiology and biotechnology , population , cell sorting , adult stem cell , stem cell marker , haematopoiesis , phenotype , hematopoietic stem cell , endothelial stem cell , cancer stem cell , flow cytometry , genetics , in vitro , demography , sociology , gene
A defining property of murine hematopoietic stem cells (HSCs) is low fluorescence after staining with Hoechst 33342 and Rhodamine 123. These dyes have proven to be remarkably powerful tools in the purification and characterization of HSCs when used alone or in combination with antibodies directed against stem cell epitopes. Hoechst low cells are described as side population (SP) cells by virtue of their typical profiles in Hoechst red versus Hoechst blue bivariate fluorescent‐activated cell sorting dot plots. Recently, excitement has been generated by the findings that putative stem cells from solid tissues may also possess this SP phenotype. SP cells have now been isolated from a wide variety of mammalian tissues based on this same dye efflux phenomenon, and in many cases this cell population has been shown to contain apparently multipotent stem cells. What is yet to be clearly addressed is whether cell fusion accounts for this perceived SP multipotency. Indeed, if low fluorescence after Hoechst staining is a phenotype shared by hematopoietic and organ‐specific stem cells, do all resident tissue SP cells have bone marrow origins or might the SP phenotype be a property common to all stem cells? Subject to further analysis, the SP phenotype may prove invaluable for the initial isolation of resident tissue stem cells in the absence of definitive cell‐surface markers and may have broad‐ranging applications in stem cell biology, from the purification of novel stem cell populations to the development of autologous stem cell therapies.