ABSTRACT
The adult vertebrate central nervous system (CNS) consists of four major differentiated cell types: neurons, astrocytes, oligodendrocytes and ependymal cells. Historically, there has been disagreement on how these differentiated cell types are generated in the CNS. Progress remains hindered by the complexity of cell structure in this system, the lack of specific cell surface markers to identify distinct cell types and the presence of numerous transit amplifying cell populations that rapidly generate early progenitors. At present it is clear that some cells, termed neural stem cells, can generate neurons as well as astrocytes and oligodendrocytes of the glial lineage both in vitro and in vivo. However, controversy still exists over whether the majority of glia in the CNS are generated by multipotential stem cells or progenitor cells that were born as committed glioblasts. Nevertheless, the existence of stem cells in the CNS has important implications for understanding both the mechanisms that generate neural diversity during embryonic development and the recruitment and differentiation of neural stem cells present in the adult. This review summarizes our knowledge of stem cells that comprise the CNS and examines the broad plasticity reported for adult CNS stem cell populations.
