Figure 4.

Altered function of niche cells for self‐renewal or differentiation of stem cells. It is hypothesized that niche cells do not autonomously determine the fate of stem cells locating near them, but stem cells might affect the niche and thus influence their behavior. In brief, when stem cells producing factor A come near the niche and factor A then stimulates the niche cells, factor B produced from the niche cells induces self‐renewal of the stem cell. In contrast, when stem cells producing factor C come near the niche and factor C stimulates the niche cells, factor D produced from the niche cells induces differentiation of the stem cell.