Main article: Cell potency
A: Stem cell colonies that are not yet differentiated.
B: Nerve cells, an example of a cell type after differentiation.
Potency specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell.[15]
- Totipotent (also known as omnipotent) stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable organism.[15] These cells are produced from the fusion of an egg and sperm cell. Cells produced by the first few divisions of the fertilized egg are also totipotent.[16]
- Pluripotent stem cells are the descendants of totipotent cells and can differentiate into nearly all cells,[15] i.e. cells derived from any of the three germ layers.[17]
- Multipotent stem cells can differentiate into a number of cell types, but only those of a closely related family of cells.[15]
- Oligopotent stem cells can differentiate into only a few cell types, such as lymphoid or myeloid stem cells.[15]
- Unipotent cells can produce only one cell type, their own,[15] but have the property of self-renewal, which distinguishes them from non-stem cells
Identification[edit]
In practice, stem cells are identified by whether they can regenerate tissue. For example, the defining test for bone marrow or hematopoietic stem cells (HSCs) is the ability to transplant the cells and save an individual without HSCs. This demonstrates that the cells can produce new blood cells over a long term. It should also be possible to isolate stem cells from the transplanted individual, which can themselves be transplanted into another individual without HSCs, demonstrating that the stem cell was able to self-renew.
Properties of stem cells can be illustrated in vitro, using methods such as clonogenic assays, in which single cells are assessed for their ability to differentiate and self-renew.[18][19] Stem cells can also be isolated by their possession of a distinctive set of cell surface markers. However, in vitro culture conditions can alter the behavior of cells, making it unclear whether the cells shall behave in a similar manner in vivo. There is considerable debate as to whether some proposed adult cell populations are truly stem cells.[20]
