Stem Cells

A stem cell is a self-renewing cell that is both the first cell of a new organism and the cell that is responsible for the renewal of adult tissues. The fertilized egg is the ultimate stem cell. Following conception, the fertilized egg divides to produce identical daughter cells, which later give rise to progeny that provide all of the cells of the developing organism. These are called embryonic stem cells (ESCs). In the adult organism, individual stem cells are responsible for not only normal tissue renewal (adult stem cells) but also for sexual reproduction (germ stem cells). The adult stem cell divides to give rise to two daughter cells, one of which remains a stem cell; the other begins the process of differentiation. Stem cells in the adult not only replace the mature dying cells of specific tissues but may also have the potential to contribute to broader repair of injured tissues. Stem cells of the adult are also the cells that give rise to cancers. It is anticipated that treatment of genetic diseases and repair of damaged organs will be accomplished by exploitation of the properties of either embryonic or adult stem cells.