Radial 'glial' progenitors: neurogenesis and signaling.

Cells with radial morphology in the developing brain were first identified more than 100 years ago. These cells, later termed radial glia, have been studied primarily as migratory scaffolds and glial progenitors. However, it has become increasingly clear, on the basis of in vitro studies and more recent in vivo fate mapping experiments, that radial glia also generate neurons during embryonic development. Now the challenge will be to understand the signaling events that regulate the spatial and temporal heterogeneity of these cells and their developmental potential. Recent work has identified the Notch, ErbB, and fibroblast growth factor signaling pathways as central to the regulation of radial 'glial' progenitors.