[Functional diversity of the hematopoietic stem cell niche]

Hematopoietic stem cells (HSCs) reside at the top of the differentiation hierarchy and differentiate into multiple hematopoietic cell lineages via a finely-tuned process. HSCs have been shown to locate in a specific microenvironment (niche) that integrates HSC function, including self-renewal, and differentiation. Accumulating evidence has revealed that various types of cells in and around the bone marrow participate in HSC function regulation as niche-comprising cells. Furthermore, recent studies have identified the stromal cells closely associated with bone marrow vasculatures as HSC niche components. The remarkable advances in experimental technologies have enabled the identification of functional differences among distinct niche cell types in the bone marrow. In this article, we review recent evidence regarding the HSC niche by focusing on the cell types associated with bone marrow vasculatures and discuss future research directions.