A stem cell is formally defined by two simultaneous properties: self-renewal, in which division yields at least one daughter that remains undifferentiated, and the capacity to differentiate into more specialized cell types — the latter capacity being quantified as potency. Potency forms a hierarchy of decreasing developmental breadth, from pluripotent cells of the blastocyst inner cell mass (capable of giving rise to every somatic cell type), to multipotent somatic stem cells (restricted to the lineages of a single tissue family), to unipotent stem cells (producing only one mature cell type), with induced pluripotent stem cells demonstrating that this progression is reversible through defined genetic reprogramming of already-specialized cells. This concept belongs to cell and developmental biology and to regenerative medicine, and it formalizes the general principle that development proceeds by progressive restriction of fate, with stem cell populations maintained at steady state by obligate asymmetric replication and stochastic differentiation and driven toward specific fates by environmental chemical signals acting against a gene-expression program that otherwise maintains the undifferentiated state.
A stem cell is formally defined by two simultaneous properties: self-renewal, in which division yields at least one daughter that remains undifferentiated, and the capacity to differentiate into more…