Stem cells appear to be fundamental cellular units associated with the origin of multicellular organisms and have evolved to function in safeguarding the cellular homeostasis in organ t- sues. The characteristics of stem cells that distinguish them from other cells have been the fascinating subjects of stem cell research. The important properties of stem cells, such as ma- tenance of quiescence, self-renewal capacity, and differentiation potential, have propelled this exciting ?eld and presently form a common theme of research in developmental biology and medicine. The derivation of...