Figure 1.

Establishment of cell polarity in cerebral cortex development. (A) The early neuroepithelium is composed of highly polarized neuroepithelial stem cells (NESCs, apical-basal polarity is indicated). NESCs give rise to radial glia progenitor stem cells (RGPCs) which exhibit even more polarized cellular morphology with an extended basal process. During neurogenesis symmetric radial glia progenitor (RGP) divisions may generate two RGPs but asymmetric divisions produce a renewing RGP and a neuron or an intermediate progenitor (IP). IPs further divide symmetrically in the subventricular zone (SVZ) to produce neurons. The basal processes of RGPs serve as a scaffold for nascent post-mitotic neurons, which migrate in a step-wise fashion coupled with changes in cell polarity, from the ventricular zone (VZ)/SVZ through the intermediate zone (IZ) in order to reach the cortical plate (CP). After nascent cortical projection neurons have delaminated from the neuroepithelium at the ventricular surface they move radially away to the SVZ exhibiting bipolar (BP) morphology. Within the SVZ/IZ, neurons “sojourn” for about 24 h or longer and most adopt a multipolar (MP) morphology, extending and retracting processes in all directions. At one point fundamental cellular polarization events take place that predetermine the future axon of the neuron before the neuron again adopts a bipolar morphology and starts locomoting along the radial glial fiber through the IZ. Once reaching the subplate (SP), neurons enter the CP and migrate towards the marginal zone (MZ) where they detach from the radial glial fiber. Finally, neurons settle in their appropriate position in the CP and the leading process will eventually become the dendrite. (B) This panel depicts the migrating neuron from panel (A) in higher detail with the leading and trailing processes which eventually become the dendrite and axon, respectively.