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The hallmarks of adult stem cells

Our knowledge about stem cells is evolving. I’d like to summarize the current understanding of adult stem cell properties as a whole. Recent research has shown there are some common features for all somatic stem cells residing in different organs. Some of these features overlap with embryonic stem cells, some are distinct.

1. Self-renewal
The most important and fundamental quality of stem cells. Self-renewal is defined as an ability of a cell to replicate itself, thereby allowing indefinite replenishment:

Self-renewal is the process by which a stem cell divides asymmetrically or symmetrically to generate one or two daughter stem cells that have a developmental potential similar to the mother cell

(definition from the review [1])

2. Multipotency
Ability to give progeny of many distinct lineages via differentiation process:

Stem cells whose progeny are of multiple differentiated cell types, but all within a particular tissue, organ, or physiological system.

(ISSCR definition [2])

Unlike adult stem cells, embryonic stem cells are pluripotent.

3. Niche
Specific anatomical location (microenvironment) within tissue where stem cell resides. Niche is ensuring self-renewal and stem cell properties via signals from surrounding cells, nervous system and mechanical cues.

4. Quiescence and specific cell cycle kinetics
Adult stem cells possess slow cell cycle kinetics with distinct large quiescent and dormant fractions. The ability of cycling stem cells to undergo quiescence and vice versa underlie the system of dynamic equilibrium.

NB: Predominant quiescence as an hallmark of adult stem cells was recently challenged for hematopoietic system [3].

5. Regenerative potential
Ability to replenish, replace or repair of mature cell types in normal or damaged (pathological) tissue. Regenerative potential could occur through such processes as: differentiation, growth factors release, fusion, horizontal genetic material transfer.

Taken together, the hallmarks indicated above define the adult stem cell. Please let me know if I have missed something.