Coexistence of Quiescent and Active Adult Stem Cells in Mammals

In the (Stem Cell) Zone

Efforts to isolate and characterize various types of stem cells have revealed much about the molecular mechanisms of stem cell self-renewal and differentiation, as well as the function of the microenvironment, or stem cell niche. Li and Clevers (p. 542 ) review what is known about stem cells in the hair follicle, bone marrow, and intestinal epithelium and suggest that two stem cell populations, one that is quiescent and one that is actively in the cell cycle, may coexist in these tissues in a so-called “zoned” stem cell model.