p57Kip2 indirectly regulates AGM HSCs

In this issue of Blood, Kapeni et al(1) reported that the deletion of p57Kip2 leads to increased proliferation of neural crest cell-derived sympathoadrenal (SA) progenitors in the mouse embryonic aorta-gonad-mesonephros (AGM) region, which in turn generates more SA cells that promote the repopulation capacity of hematopoietic stem cells (HSCs) by secreting catecholamines.