Embryonic stem cells are derived from embryos, specifically the inner cell mass of a blastocyst, a hollow ball of cells that forms approximately five days after conception. Embryonic stems cells are the most primitive stem cells and as a result contain the most long-term promise for novel cell therapies and tissue regeneration.
Embryonic stem cells are derived from embryos at a developmental stage before the time that implantation would normally occur in the uterus. Fertilization normally occurs in the oviduct, and during the next few days, a series of cleavage divisions occur as the embryo travels down the oviduct and into the uterus. Each of the cells (blastomeres) of these cleavage-stage embryos are undifferentiated, i.e. they do not look or act like the specialized cells of the adult, and the blastomeres are not yet committed to becoming any particular type of differentiated cell. Indeed, each of these blastomeres has the potential to give rise to any cell of the body. The first differentiation event in humans occurs at approximately five days of development, when an outer layer of cells committed to becoming part of the placenta (the trophectoderm) separates from the inner cell mass (ICM). The ICM cells have the potential to generate any cell type of the body, but after implantation, they are quickly depleted as they differentiate to other cell types with more limited developmental potential. However, if the ICM is removed from its normal embryonic environment and cultured under appropriate conditions, the ICM-derived cells can continue to proliferate and replicate themselves indefinitely and still maintain the developmental potential to form any cell type of the body. These pluripotent, ICM-derived cells are ES cells.
Embryonic stem cells are pluripotent, meaning they have the ability to differentiate into any of the 200-plus cell types required by the body. These pluripotent stem cells can give rise to all tissues, including the complete spectrum of mesoderm, endoderm, and ectoderm derivatives. Multiple ESC lines have been derived from a wide range of species, ranging from mouse to human. Human ESCs have now been demonstrated to give rise to various cell types, including hematopoietic cells, neuron-like cells, glial progenitors, dendritic cells, hepatocytes, pancreatic islet-like cells, osteocytes, chondrocytes, adipocytes, cardiomyocytes, as well as muscular, endothelial, skin, lung, and retinal tissues. This quintessential differentiation potential provides a promising avenue to produce a large quantity of transplantable cells from a renewable source.
Understanding and controlling embryonic stem cell differentiation and growth will require years of intensive research. Growing these cells in the laboratory is a time-consuming and painstaking process. Scientists must monitor embryonic stem cells closely and provide constant care to ensure continued growth and prevent uncontrolled or spontaneous differentiation. Most embryonic stem cells used for research today have been donated from excess blastocysts created during in-vitro fertilization.
- What stages of early embryonic development are important for generating embryonic stem cells
- How are embryonic stem cells grown in the laboratory
- human ES cell lines
- What laboratory tests are used to identify embryonic stem cells
- How are embryonic stem cells stimulated to differentiate
