Pushpam Kumar Sinha
Abstract
It is a commonly held belief nowadays that cancer originates in tissue-specific adult stem cells. Most of the tissues in human body have adult stem cells at their base. The difference between embryonic stem cell and adult stem cell is that whereas the former, through a carefully orchestrated cellular program of development genes, can give rise to terminally differentiated cells of all types, the later can repair the terminally differentiated tissue by giving rise to cells of few types specific to the tissue. In a majority of tissues the adult stem cells are relatively quiet, swinging into action only on signals of damage or injury to tissue. One of the exceptions of this is the adult stem cell of intestinal epithelium, which is continuously in action as the differentiated cells of intestinal epithelium are continuously shed into the lumen. The adult stem cells have the property of self-renewal: they can undergo asymmetric cell division to give rise to two distinct daughter cells one of which is the exact copy of mother stem cell and the other is a partially differentiated progenitor cell or progeny, and symmetric cell division to give rise to two identical daughter cells which are exact replicas of mother stem cells.