PerspectiveSTEM CELLS

Potency finds its niches

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Science  08 Jan 2016:
Vol. 351, Issue 6269, pp. 126-127
DOI: 10.1126/science.aae0325

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Hematopoietic stem cells (HSCs) located atop the hematopoietic hierarchy are responsible for the lifelong production of all mature blood cells. These partly dormant, long-term self-renewing, multipotent HSCs in the bone marrow generate multipotent progenitors (MPPs) with reduced self-renewal activity before lineage determination and differentiation are initiated (1, 2). For decades, it was thought that MPPs lose their multipotent capacity in a stepwise fashion, generating first a series of oligopotent and from there unipotent progenitors to finally make all hematopoietic cell types. The presence of oligopotent intermediates such as common lymphoid progenitors (CLPs) and common myeloid progenitors (CMPs) is crucial to this model because they define the path from multipotent to unipotent cells. A study by Notta et al. on page 139 of this issue (3) and another study by Paul et al. (4) provide strong evidence for the nonexistence of CMPs in human and mouse bone marrow. And on page 176 of this issue, Khan et al. (5) report a niche population in the fetal liver that maintains proliferating HSCs.