Changes in cerebral cortex size are governed by fibroblast growth factor during embryogenesis

We show that fibroblast growth factor 2 (FGF2) and FGF receptors are transi ently expressed by cells of the pseudostratified ventricular epithelium (PV E) during early neurogenesis. A single microinjection of FGF2 into cerebral ventricles of rat embryos at E15.5 increased the volume and total number o f neurons in the adult cerebral cortex by 18% and 87%, respectively. Microi njection of FGF2, by the end of neurogenesis, at E20.5, selectively increas ed the number of glia. Mice lacking the FGF2 gene had fewer cortical neuron s and glia at maturity. BrdU studies in FGF2-microinjected and FGF2-null an imals suggested that FGF2 increases the proportion of dividing cells in the PVE without affecting the cell-cycle length. Thus, FGF2 increases the numb er of rounds of division of cortical progenitors.