[sciencell]

Stem cells, by definition, can undergo infinite number of cell division while remain in an undifferentiated state. However, they can also give rise to differentiated daughter cells that are committed to specialized cell fate in all three primary germ layers: ectoderm, mesoderm and endoderm. During embryogenesis, the degree of this differentiation becomes gradually restricted as the fetus develops and the potential of various stem cells is limited by the class they belong to. While both totipotent and pluripotent stem cells can generate every type of cells found in the body, only totipotent ones are able to form an entire organism. In contrast, multipotent stem cells are more mature in developmental age compared to totipotent and pluripotent stem cells, and therefore, can only give rise to a limited population of cells within a specific lineage.

The particularly extrinsic and intrinsic molecular signaling network that confers their self-renewal and differentiation remain fairly uncharacterized. However, a consistent requirement for the Oct4, Nanog and Sox2 transcription factors in maintaining pluripotency seems to be evolutionarily conserved between mouse and human.