STEM
CELLS IN THE CNS: INTRINSIC AND EXTRINSIC MECHANISMS
Embryogenesis involves
the proliferation of stem cells, followed by differentiation and migration of
the resultant cell types. In the CNS, derived from the neural tube, neuronal
stem cells persist in the subventricular (or subependymal) zone of
the lateral ventricles (I).
Waves of neuronal proliferation, differentiation,
and migration occur during prenatal CNS development. After birth, stem cells in
the subventricular zone continue to proliferate and produce granule cells
(neurons) for many brain regions; this process is driven by postnatal
environmental stimuli. Throughout adulthood, in the sub-granular zone of
the dentate gyrus, radial glial-like cells give rise to neuroblasts that
contribute new granule cell neurons (II). In addition, oligodendroglial progenitor
cells throughout the CNS can proliferate and then differentiate into mature
oligodendrocytes (III). This process can occur after a demyelinating lesion and
helps to remyelinate CNS axons (e.g., after a multiple sclerosis lesion).
