It is now known that in the adult, pools of neuroepithelial stem cells are retained in the central nervous system (CNS) (e.g., hippocampus, subventricular zone, olfactory bulb, and spinal cord) (11,14,39). Neural crest-derived stem cells in the peripheral nervous system (PNS) have recently been isolated and characterized from sensory neurons in dorsal root ganglia (DRG) (25) and trigeminal ganglia (23). The neural stem cells (NSCs) in PNS are particular interesting in that, compared to CNS stem cells, those in the DRG remain devoid of trophic influences of a ventricular system. The conservation of stem cells in the PNS is less understood than that of the CNS. Furthermore, the NSCs in the CNS, disregarding embryonic or adult origin, once isolated from their local environment, adopt various differential pathways and lose their phenotype potentials. The typical example is that the embryonic stem cells screened from the substantia nigra largely lose their ability to express dopamine neurons (3,27). It is unclear how long the neural crest-derived stem cells can be preserved without loosing their stem cell potency and how much differential potency is
