Regulation of niche molecules for the maintenance of cardiac stem cells.

Bone marrow (BM) transplantation was the first application utilizing stem cells for tissue regeneration therapy, exploiting the function of HSCs for differentiation into all cells of the hematopoietic lineage. BM reconstitution is maintained long term by the self-renewal activity of HSCs. Transfusions of red blood cells or platelets remain important for transient treatment of hematopoietic deficiencies, but stem cell transplantation is required for whole tissue/organ regeneration. At the present time, methods to generate tissue/organ-specific terminallydifferentiated cells from immature cell types, such as ES and iPS cells, have been established; we need to keep in mind that issue/organ specific stem cells play central roles in the formation, development and maintenance of most organs and are thought to be crucial cell populations for tissue regeneration therapies. The first definitively identified stem cell populations were the hematopoietic stem cells (HSCs). Since then, many stem cell populations have been isolated and gradually tissue/organ-specific stem cells have been identified in diverse organs such as brain, skin and colon. A single stem cell generates large numbers of terminally-differentiated tissue/organ-specific cells via its differentiation into progenitor cells; however, it must retain the ability to divide asymmetrically, whereby 1 daughter cell retains stemness. The latter event is designated self-renewal and, by means of this property of stem cells, turnover of tissue-specific cells is maintained. T