It has synthesized recent findings (including our own) on stem cell niches and their functions. The findings summarized in this review have supported an essential role of the niche in regulation of the balance between stem cell self-renewal and differentiation in vivo. This review has also provided a list of outstanding unanswered questions related to stem cell niches.

Stem cells require a special environment or a niche for their survival and function in the body. When stem cells are isolated and put onto culture dishes, they tend to lose their properties and undergo either differentiation or senescence.

Identification of intimate partners (niche cells) for these stem cells will be helpful to understand how stem cells are maintained in the body, as well as to expand stem cells on dishes for future cell therapy. This review intends to give stem cell researchers an updated summary of findings on stem cell niches, and to help the researchers who are interested in stem cells, but have not yet worked on them, to get into the field. We truly hope that this review makes more scientists become interested in stem cell niches and thus helps advance future stem cell research.