The classical definition of a stem cell requires that it possess two properties:
- Self-renewal - the ability to go through numerous cycles of cell division while maintaining the undifferentiated state.
- Potency - the capacity to differentiate into specialized cell types. In the strictest sense, this requires stem cells to be either totipotent or pluripotent - to be able to give rise to any mature cell type, although multipotent or unipotent progenitor cells are sometimes referred to as stem cells.
Potency definitions
''Potency'' specifies the differentiation potential (the potential to differentiate into different cell types) of the stem cell.
- Totipotent (a.k.a omnipotent) stem cells can differentiate into embryonic and extraembryonic cell types. Such cells can construct a complete, viable, organism.
- Multipotent stem cells can differentiate into a number of cells, but only those of a closely related family of cells. As well, stem cells can be isolated based on a distinctive set of cell surface markers. However, ''in vitro'' culture conditions can alter the behavior of cells, making it unclear whether the cells will behave in a similar manner ''in vivo''. Considerable debate exists whether some proposed adult cell populations are truly stem cells.
Further Reading
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