Niches are local tissue microenvironments that maintain and regulate stem cells. Haematopoiesis provides a model for understanding mammalian stem cells and their niches, but the haematopoietic stem cell (HSC) niche remains incompletely defined.
Outstanding questions concern the cellular complexity of the niche, the role of the endosteum and functional heterogeneity among perivascular microenvironments. Haematopoietic stem cell (HSC) niches are present in diverse tissues throughout development, beginning in the aorta–gonad–mesonephros (AGM) region and the yolk sac, followed by the placenta, fetal liver, spleen and bone marrow.
Postnatally, the bone marrow is the primary site of HSC maintenance and haematopoiesis, but in response to haematopoietic stress the niche can shift to extramedullary sites. Defining niche components and how they work in concert to regulate haematopoiesis provides the opportunity to improve regeneration following injury or HSC transplantation and to understand how disordered niche function could contribute to disease. (Nature 505, 327–334 (16 January 2014) doi:10.1038/nature12984)