Radial glias and radial fibers: what is the function of radial fibers?

Radial glias have been thought to serve as a scaffold to support and direct neurons in their radial migration during the development of the cerebral cortex. However, a recent series of studies on neocortical development showed that these cells behave as multifunctional cells. These studies have provided strong support for the idea that radial glias function as multipotential progenitor cells that give rise to various cell types, including neurons. Proliferation of the radial glia was thought to result in inheritance of the radial fiber by a postmitotic neuron, and it was considered that one role of the radial fiber was to act as a cable to lift the postmitotic neuron. In this review, we propose another function of the radial fiber in the developing neocortex. This novel function is proposed based on the fact that the characteristics of the radial glias are identical to those of neuroepithelial cells. Before neuron production, the neuroepithelial cells proliferate and increase in number, retaining and reproducing radial fibers attached to the surface of the basement membrane (the pia mater). During neuron production, the radial glias also reproduce radial fibers at the time of each cell division. We believe that the radial fiber functions to receive signals for morphogenesis, proliferation and differentiation from the pia mater and acts as a cable to conduct information transduced from such signals to the cell soma.