Figure 2.

Different models of stem cell division. In model A, each stem or progenitor cell gives rise to a different cell type requiring a different stem cell population for each tissue. Models B and C demonstrate the possibility of a multipotent stem cell generating different types of precursors by asymmetric division. Model B presupposes stem cell maturation over time in response to extrinsic signals, thus it does not generate truly identical daughter cells. Model D displays a model of symmetric cell division without the necessity of asymmetric division.