Bridges between Cell Cycle Regulation and Self-Renewal Maintenance.

Stem cells are a unique population that lies at the summit of any, or at least most, biological systems. They can differentiate in a variety of mature cell types, but they also have the ability to self-renew, that is, the capacity to divide and retain all the features of the mother cell. The regulation of self-renewal has been studied for many years, but several aspects of this regulation are still vague. The combined decision to divide and self-renew or differentiate suggests that the mechanisms that regulate self-renewal and cell cycle activity are intermingled. While inactivation of many cell cycle regulators impacts the physiological and pathological biology of stem cells, the exact mechanisms that link the decision to enter the cell cycle and the choice of the cellular fate are poorly understood. The multiplicity of signals and pathways regulating self-renewal add to the complexity of the phenomenon. Here, I will review the described links between the cell cycle and self-renewal and discuss the role of the niche in the regulation of both mechanisms.