The bone marrow environment is critical for regulating the quiescence and proliferation of hematopoietic stem cells (HSCs). In Nature, Kinisaki et al. show that quiescent HSCs associate specifically with small arterioles that are preferentially found in the endosteal bone marrow. Dormant HSCs associate with rare NG2+ periarteriolar pericytes, which are also quiescent and have higher expression of genes associated with 'HSC niche' activity. Depletion of NG2+ cells diminishes the pool of long-term repopulating HSCs in the bone marrow. Pharmacological or genetic activation of the HSC cycle alters the distribution of HSCs from NG2+ periarteriolar niches to LEPR+ perisinusoidal niches. These results indicate that there are spatially distinct, arteriolar and sinusoidal niches for quiescent HSCs versus proliferating HSCs in the bone marrow.

Nature (9 October 2013) doi:10.1038/nature12612