Figure 2.

IFNα induces activation of HSCs in vivo. In vivo treatment of mice with the cytokine IFNα induces cell cycle entry of dormant and homeostatic HSCs as well as multipotent progenitors (MPPs). IFNα signaling leads to rapid phosphorylation of STAT1 and PKB, as well as activation of a set of IFNα target genes. The IFNα response is also associated with a robust up‐regulation of the stem cell marker Sca‐1 (red) on the cell surface of stimulated cells. This up‐regulation of Sca‐1 is required for the IFNα‐mediated activation and proliferation of stem/progenitors, since dHSCs lacking Sca‐1 no longer divide in response to IFNα.