Spatial Peculiarities of Stem Cells in Plants and Animals

 The life of any organism begins at the level of stem cells. The fertilized egg considered as ultimate stem cell, divides to give rise to lines of cells that form various differentiated organs. During these early divisions, each daughter cell retains totipotency. Then, through a series of divisions and differentiations, the embryonic stem cells (ESCs) lose potential and gain differentiated function. During normal tissue renewal in adult organs, tissue stem cells give rise to progeny that differentiate into mature functioning cells of that tissue. Stem cells which are not totipotent are called “progenitor cells”[1].   Stem cells display specific characteristic to be called as stem cells. The first characteristic of stem cells is that they are naïve cells- meaning that they either expresses very little cell surface markers of differentiation or no cell surface marker of differentiation. Second characteristic is asymmetric cell division, which is responsible for the self renewal of the stem cell pool[1,2]. During early embryonic development, each cell divides and gives rise to two daughter cells with the same potential: symmetric division. During normal tissue renewal in the adult, each progenitor cell gives rise to one daughter cell that remains a progenitor cell, and one daughter cell that begins the process of determination to a terminally differentiated cell-asymmetric division.