Pushpam Kumar Sinha
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.