Growth factor influences on the production and migration of cortical neurons.

Production of neurons from progenitor cells is the first step in building the complex, six-layered cerebral cortex. The neurons that will populate the mature cortex are produced during development in an active proliferative neuroepithelium, the ventricular zone (VZ), adjacent to the cerebral ventricle (Rakic 1975; McConnell 1995; Caviness et al. 1996; Ross 1996). The first postmitotic neurons move out of the ventricular zone to form the preplate, just beneath the pia. Subsequent neuronal cohorts, generated in the neo-cortical ventricular zone, move into the preplate to form the cortical plate, which will eventually become layers 2 through 6 of cortex. At the earliest stages of cortical plate formation, preplate neurons are divided into two layers, the marginal zone, above the cortical plate, and the subplate, below it (Marin-Padilla 1971; Luskin and Shatz 1985; Allendoerfer and Shatz 1994). Many neurons move into the cortical plate under the guidance of the processes of radial glia (Hatten 1990; Rakic et al. 1994), but others, arising in distant proliferative zones, migrate tangentially into cortex, guided by cues that have not been defined (reviewed in Pearlman et al. 1998).