title: Sca+CD34- murine side population cells are highly enriched for primitive stem cells.
abstract: OBJECTIVE
  The aim of this study was to characterize murine side population (SP) stem cells and SP cell subpopulations for primitive stem cell capacity.
  
  
  METHODS
  SP cells, characterized by a specific Hoechst dye efflux pattern, were isolated by flow cytometric analysis and sorting from murine adult whole bone marrow (WBM). Different subpopulations of SP cells were isolated by staining with anti-Sca and anti-CD34 antibodies. Primitive stem cell content of SP cells and SP subsets were determined by cobblestone area-forming cell (CAFC) frequencies.
  
  
  RESULTS
  Measurement of CAFC frequencies revealed that SP cells are greatly enriched for both primitive stem cells (day-28-35 CAFC) and somewhat more mature hematopoietic cells (day-14-21 CAFC) compared to WBM. The day-28 and day-35 CAFC enrichments in SP cells vs WBM cells were 1065 and 471, respectively. Analysis of the subpopulations of SP cells revealed that SP(+)Sca(-)CD34(+) cells contained almost exclusively day-7 CAFC and had little day-28-35 CAFC activity. SP(+)Sca(+)CD34(+) cells had high day-7-14 CAFC frequencies, but lower day-35 CAFC frequencies compared to SP(+)Sca(+)CD34(-) cells. SP(+)Sca(+)CD34(-) cells contained very low day-7 CAFC activity, but nearly 2200 times the day-28-35 CAFC activity as normal bone marrow. To evaluate the influence of Hoechst dye efflux capacity, we divided the SP tail into four groups of cells. The SP cells with lowest efflux of Hoechst dye contained the highest progenitor activity (day-7-14 CAFC). The highest day-35 CAFC frequencies, nearly 6000 times those of normal marrow, were seen in the SP cells with the greatest efflux of the Hoechst dye.
  
  
  CONCLUSIONS
  Murine SP cells contain both progenitor and primitive populations of hematopoietic stem cells. The most primitive stem cells measured in the in vitro CAFC assay mark for Sca(+) and CD34(-) and have a high ability to efflux Hoechst dye. Isolation of these cells may provide the means to directly study mechanisms of primitive stem cell damage.
authors.affiliation: Department of Radiation Oncology, Brigham and Women's Hospital, and the Dana-Farber Cancer Institute, Harvard Medical School, Boston, Mass 02115, USA.
authors.forename: Kalindi
authors.initials: K
authors.lastname: Parmar
authors.forename: Calies
authors.initials: C
authors.lastname: Sauk-Schubert
authors.forename: Daniel
authors.initials: D
authors.lastname: Burdick
authors.forename: Maris
authors.initials: M
authors.lastname: Handley
authors.forename: Peter
authors.initials: P
authors.lastname: Mauch
mesh_terms: D000818:Animals; D018952:Antigens, CD34 / Q000032:analysis; D000943:Antigens, Differentiation / Q000032:analysis; D001562:Benzimidazoles; D001854:Bone Marrow Cells / Q000166:cytology / Q000276:immunology; D018929:Cell Culture Techniques; D005434:Flow Cytometry; D005456:Fluorescent Dyes; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000276:immunology; D008297:Male; D051379:Mice
chemical_list: D018952:Antigens, CD34; D000943:Antigens, Differentiation; D001562:Benzimidazoles; D005456:Fluorescent Dyes; C047076:senescent cell differentiation antigen; C017807:bisbenzimide ethoxide trihydrochloride