The role of IFN-α during embryonic hematopoiesis. Although IFN-γ has been reported to play a role in promoting emergence of HSCs, Kim et al show that IFN-α promotes the next step in development of HSCs: the maturation of AGM HSCs. In this process, IFN-α signals parallel to Arid3a, with Arid3a being a transcriptional co-regulator of IFN effector genes. Therefore, when Arid3a is absent, IFN signaling in AGM HSCs is dampened. Exogenous IFN-α treatment of AGM HSCs will lead to saturation of the system with STAT1, overcoming this defect. See the complete Figure 7 in the article by Kim et al that begins on page 204.