Figure 1.

Cortical development at different stages in humans and the equivalent time line in mice. (A) As the neural tube develops, it enlarges into three vesicles corresponding to the forebrain, midbrain, and hindbrain regions of the adult brain. At this stage, the neural tube wall has a single layer of neuroepithelial cells (NECs). These cells migrate to the lumen of the neural tube to divide, a phenomenon also known as interkinetic nuclear migration. (B) At the midstage of neurogenesis, apical radial glial cells (aRGCs) that derived from NECs can undergo either symmetric division to expand the progenitor pool size or asymmetric division, giving rise to basal RGCs (bRGCs) or intermediate progenitors (IPs). Note that bRGCs are almost absent in rodents. bRGCs, IPs, and aRGCs will eventually generate postmitotic neurons that migrate toward the pial surface. (VZ) Ventricular zone, (SVZ) subventricular zone, (IZ) intermediate zone, (CP) cortical plate. (C) The fully formed adult cerebral cortex consists of six layers of neurons.