Figure 1.

Schematic representation of different types of stem cells. (a) ESCs are derived from the inner cell mass of the blastocyst and can be cultured in vitro as colony-forming cells. (b) Adult pluripotent stem cells, derived from a totipotent cell, differentiate in tissue-specific committed cells, which contribute to tissue homeostasis and regeneration by forming adult terminally differentiated cells. (c) In pathological conditions, normal cells or stem cells can accumulate genetic mutations and can transform into cancer-initiating cells with stem-like features, which can take over the other cells, forming the tumor mass.