Stem Cell Niches

The 2007 review by V V Terskikh et al. discussed the nature of stem cell niches and their interaction with stem cells. Stem cell niches, which are formed during ontogeny, can exist independently of stem cells and can remain vacant. However, stem cell self-renewal cannot be maintained for long periods outside of the niche except under specific conditions, such as in vitro. These niches can be occupied by excessive or transplanted stem cells and can support their functioning. The size of a niche determines the number of stem cells it can maintain. Excessive stem cells either differentiate in the presence of a specific signal or undergo apoptosis in the absence of such signal. The niches control the number of stem cells in the body and protect it from excessive stem cell proliferation. Under certain conditions, stem cells can leave and return to their niches. Stem cells are retained in the niche by cell-to-cell interactions and adhesion to the extracellular matrix. Both the niches and stem cells arise at a particular ontogenetic stage and are capable of long self-renewal.