Minireview: The stem cell next door: skeletal and hematopoietic stem cell "niches" in bone.

Long known to be home to hematopoietic stem cells (HSC), the bone/bone marrow organ and its cellular components are directly implicated in regulating hematopoiesis and HSC function. Over the past few years, advances on the identity of HSC "niche" cells have brought into focus the role of cells of osteogenic lineage and of marrow microvessels. At the same time, the identity of self-renewing multipotent skeletal progenitors (skeletal stem cells, also known as mesenchymal stem cells) has also been more precisely defined, along with the recognition of their own microvascular niche. The two sets of evidence converge in delineating a picture in which two kinds of stem cells share an identical microanatomical location in the bone/bone marrow organ. This opens a new view on the manner in which the skeleton and hematopoiesis can cross-regulate via interacting stem cells but also a novel view of our general concept of stem cell niches.