The Bone Marrow Microenvironment for Hematopoietic Stem Cells.

The main function of the microenvironment in the bone marrow (BM) is to provide signals that regulate and support the production of the billions of blood cells necessary to maintain homeostasis. The best characterized BM microenvironment is the niche that regulates hematopoietic stem cells. Efforts from many different laboratories have revealed that the niche is mainly perivascular and that blood vessels and perivascular stromal cells are the key components. In addition numerous cell types have been shown to be components of the niche. Here we discuss our current understanding of the niche and the evidence supporting the role of different types of cells in regulating hematopoietic stem cell numbers and function in vivo.