ABSTRACT
The life-long maintenance of adult self-renewing tissues, including the hematopoietic system, the skin and the intestinal epithelium is dependent on adult stem cells. These cells have the intrinsic capability to self-renew, therefore producing cells of the same kind, as well as to differentiate, giving rise to more committed progenitor and differentiated cells to maintain their host tissue. Many terminally differentiated cells of the hematopoietic system, such as granulocytes, have rapid turnover rates and therefore need to be constantly replaced during homeostasis. Additionally, during hematopoietic stress conditions such as bleeding or toxic insult, the demand for production of new blood cells is further increased. In order to maintain the integrity of the system also under such conditions, hematopoietic stem and progenitor cells have to be able to sense such injuries and rapidly produce new blood cells.
