EMBRYONIC STEM CELLS (ESCS)

The embryonic stem cell is defined by its origin in the embryo. The fertilized egg has unbounded sternness. At this stage it is totipotent and can create all kinds of cells. Totipotency is limited to only one or two divisions. As the egg becomes a blastocyst and before it implants in the uterus, the hollow round ball develops a clump of cells—the inner cell mass—and becomes pluripotent. Embryonic stem cells are harvested exclusively from this inner cell mass in the blastocyst. When placed in a cell culture in vitro, ESCs differentiate into many kinds of cells. which are shown in all three germ layers. But because the induction or communication process is disrupted between the 1CM and the trophoblast. the cells can generate only embryonic germ cells that will not become a human embryo. This remarkable feat of the ESC was first shown in the l980s. using the 1CM of a mouse blastocyst. In the culture dish, cell-to-cell communicationled to the formation of nerve, skin, and other cells. But without the surrounding layers of the trophoblast. they received no signals from the mother’s

uterus. The cells became like wandering boys. able to make all the necessary differentiated cells but unable to put them together to become living beings.