Stem-cell niche refers to a microenvironment, within the specific anatomic location where
stem cells are found, which interacts with stem cells to regulate cell fate. The word 'niche' can be in reference to the
in vivo or
in vitro stem-cell microenvironment. During embryonic development, various niche factors act on embryonic stem cells to alter gene expression, and induce their proliferation or differentiation for the development of the fetus. Within the human body, stem-cell niches maintain adult stem cells in a quiescent state, but after tissue injury, the surrounding micro-environment actively signals to stem cells to promote either self-renewal or differentiation to form new tissues. Several factors are important to regulate stem-cell characteristics within the niche: cell–cell interactions between stem cells, as well as interactions between stem cells and neighbouring differentiated cells, interactions between stem cells and adhesion molecules, extracellular matrix components, the oxygen tension, growth factors, cytokines, and the physicochemical nature of the environment including the pH, ionic strength (e.g.
Ca2+ concentration) and metabolites, like
ATP, are also important. The stem cells and niche may induce each other during development and reciprocally signal to maintain each other during adulthood.