Characterization and localization of side population cells in mouse skin

Stem Cells. Jun-Jul 2005;23(6):834-41. doi: 10.1634/stemcells.2004-0226.


Recently, the detection of side population (SP) cells, which have the ability to strongly efflux Hoechst 33342 fluorescence dye, has attracted attention as a method of stem cell isolation. We identified SP cells from mouse skin using the same method as from bone marrow. This population almost completely disappeared after treatment with the calcium channel blocker verapamil. SP cells were mainly localized in the epidermis, with a few in the dermis. The ratio of SP cells decreased as the mouse became older. Surface marker analysis revealed that the sorted SP cells expressed alpha6-integrin, beta1-integrin, Sca-1, keratin 14, and keratin 19, which are proliferating and progenitor cell markers, at levels higher than in non-SP cells, while they expressed E-cadherin, CD34, and CD71 at lower levels. The expression of breast cancer resistance protein 1 (BCRP1), which participates in dye efflux, was expressed at high levels at both the protein and mRNA level in sorted SP cells. Immunohistochemical analysis showed that BCRP1 was expressed in the basal layers and hair bulge regions of mouse skin. BCRP1 mRNA was found in basal layers and hair follicles of newborn skin by in situ hybridization. These results indicate that the localization of BCRP1-positive cells is compatible with that of keratinocyte stem cells. Based on the close relationship between BCRP1 and the SP cell phenotype, we conclude that keratinocyte stem cells are closely related to the SP- or BCRP1-positive cells.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, CD / biosynthesis
  • Antigens, CD34 / biosynthesis
  • Antigens, Ly / biosynthesis
  • Benzimidazoles / pharmacology
  • Blotting, Western
  • Bone Marrow Cells / cytology
  • Cadherins / biosynthesis
  • Cell Membrane / metabolism
  • Dermis / cytology
  • Epidermal Cells
  • Immunohistochemistry
  • In Situ Hybridization
  • Integrin alpha6 / biosynthesis
  • Integrin beta1 / biosynthesis
  • Keratin-14
  • Keratinocytes / cytology
  • Keratins / biosynthesis
  • Ki-67 Antigen / biosynthesis
  • Membrane Proteins / biosynthesis
  • Mice
  • Phenotype
  • RNA, Messenger / metabolism
  • Receptors, Transferrin / biosynthesis
  • Reverse Transcriptase Polymerase Chain Reaction
  • Skin / cytology*
  • Stem Cells / cytology
  • Time Factors
  • Verapamil / pharmacology


  • Antigens, CD
  • Antigens, CD34
  • Antigens, Ly
  • Benzimidazoles
  • CD71 antigen
  • Cadherins
  • Integrin alpha6
  • Integrin beta1
  • Keratin-14
  • Ki-67 Antigen
  • Krt14 protein, mouse
  • Ly6a protein, mouse
  • Membrane Proteins
  • RNA, Messenger
  • Receptors, Transferrin
  • Keratins
  • Verapamil
  • bisbenzimide ethoxide trihydrochloride