Are Embryonic Stem Cells Truly Pluripotent?
Pluripotency—that is the ability to give rise to differentiated cell types that are derived from all three primary germ layers of the embryo, endoderm, mesoderm, and ectoderm—is what makes ES cells unique. How do we know that these cells are, indeed, pluripotent? Laboratory-based criteria for testing the pluripotent nature of ES cells derived from mice include three kinds of experiments [19]. One test is conducted by injecting ES cells derived from the inner cell mass of one blastocyst into the cavity of another blastocyst. The “combination” embryos are then transferred to the uterus of a pseudopregnant female mouse, and the progeny that result are chimeras. Chimeras are a mixture of tissues and organs of cells derived from both donor ES cells and the recipient blastocyst. This test has been extended in studies designed to test whether cultured ES cells can be used to replace the inner cell mass of a mouse blastocyst and produce a normal embryo. They can, but the process is far less ef
