Radial glia phenotype: Origin, regulation, and transdifferentiation

Radial glial cells play a major guidance role for migrating neurons during central nervous system (CNS) histogenesis but also play many other crucial roles in early brain development. Being among the earliest cells to differe ntiate in the early CNS, they provide support for neuronal migration during embryonic brain development; provide instructive and neurotrophic signals required for the survival, proliferation, and differentiation of neurons; a nd may be multipotential progenitor cells that give rise to various cell ty pes, including neurons. Radial glial cells constitute a major cell type of the developing brain in numerous nonmammalian and mammalian vertebrates, in creasing in complexity in parallel with the organization of the nervous tis sue they help to build. In mammalian species, these cells transdifferentiat e into astrocytes when neuronal migration is completed, whereas, in nonmamm alian species, they persist into adulthood as a radial component of astrogl ia. Thus, our perception of radial glia may have to change from that of pat h-defining cells to that of specialized precursor cells transiently fulfill ing a guidance role during brain histogenesis. In that respect, their appar ent change of phenotype from radial fiber to astrocyte probably constitutes one of the most common transdifferentiation events in mammalian developmen t. (C) 2000 Wiley-Liss, Inc.