The hematopoietic stem cell niche: What's so special about bone?

Hematopoietic stem cells (HSCs) require a supportive microenvironment to regulate their function and produce sufficient hematopoietic cells over the lifetime of an individual. With the exception of fish, all vertebrates, including mammals, maintain HSCs in a complex niche within the bone marrow. Several bone specific cellular populations have been implicated as components of the HSC niche and are part of a complex network that regulates HSC functions. However, the full extent of interactions within the HSC niche, and the role of individual cell populations remain to be fully elucidated. Further, it is not clear why fish are the exception, and what advantage is gained by housing HSCs in the bone marrow. To gain a better understanding of hematopoiesis and the mechanisms that drive hematopoietic disease processes a clearer picture of the complex HSC regulatory interactions in the bone marrow microenvironment is required.