Murine epidermal label-retaining cells isolated by flow cytometry do not express the stem cell markers CD34, Sca-1, or Flk-1

Keratinocyte stem cells are present in the murine epidermis, based on both in vitro and in vivo evidence, and better characterization of these cells r emains an active goal. Because keratinocyte stem cells are believed to cycl e slowly, a good method for identification is based on their ability to ret ain nucleoside analog, such as bromodeoxyuridine. Adult stem cells have bee n identified in other tissues, including hematopoietic, neural, and skeleta l muscle, and stem cell surface markers have been characterized. We wanted to determine if cell-surface markers present on both hematopoietic and skel etal muscle stem cells (CD34, Sca-1, and Flk-1) were also present on kerati nocyte stem cells, and could be used to identify them. The cell-surface exp ression of cells that retained bromodeoxyuridine label for at least 21 d wa s compared with that of nonlabel-retaining cells. Double-labeling for flow cytometric analysis was employed, and label-retaining cells were found to l ack expression of the tested markers. beta1 integrin levels were also evalu ated, and although high expression was found on label-retaining cells, it w as not specific for these cells.