Stem cell niche in tissue homeostasis, aging and cancer.

Stem cells have an essential role in tissue homeostasis, repair, and regeneration of a tissue or an organ. Stem cells are immature cells having unlimited ability of self-renewal and capacity to differentiate into specialized cell types. Proper regulation of these dual properties is critical in animal development, growth control, and reproduction. Accumulating evidences suggest that stem cell behavior is regulated by both extracellular signals from the niche cells and intrinsic signal within stem cells. Using diverse model systems, tremendous work has been done to understand how niche control the stem cell self-renewal and differentiation. This review presents the progress made in stem cell niche field in germline and somatic stem cells in lower organism and mammals. The knowledge gained by studying the stem cells and its niches in diverse model organisms and the molecular mechanisms regulate their behavior are vital in understanding tissue homeostasis, regeneration, aging and cancer in humans.