The forkhead O (FoxO) family of transcription factors participates in diverse 
physiologic processes, including induction of cell-cycle arrest, stress 
resistance, differentiation, apoptosis, and metabolism. Several recent studies 
indicate that FoxO-dependent signaling is required for long-term regenerative 
potential of the hematopoietic stem cell (HSC) compartment through regulation of 
HSC response to physiologic oxidative stress, quiescence, and survival. These 
observations link FoxO function in mammalian systems with the evolutionarily 
conserved role of FoxO in promotion of stress resistance and longevity in lower 
phylogenetic systems. Furthermore, these findings have implications for aging in 
higher organisms and in malignant stem cell biology, and suggest that FoxOs may 
play an important role in the maintenance and integrity of stem cell 
compartments in a broad spectrum of tissues.