Stem Cell Ground State

During embryonic development in mammals, the first step is the formation of the zygote by fertilization of the egg by the sperm. Following fertilization, the zygote undergoes multiple cell division cycles called cleavages to generate the morula, an early stage in the development of an embryo. This stage is followed by an arrangement of the cells into several layers. The outer layer, or the trophoblast, eventually forms the placenta and the inner layer, known as the inner cell mass (ICM), forms the actual embryo. This two-layered structure, which is present before the embryo attaches itself onto the walls of the uterus, is known as the blastocyst.

The ICM is composed of pluripotent stem cells that can generate every cell type in the body and has been ...