Differential origins of neocortical projection and local circuit neurons: Role of Dlx genes in neocortical interneuronogenesis

Herein we review the evidence that neocortical projection neurons and interneurons are derived from distinct regions within the telencephalon. While neocortical projection neurons are derived from the ventricular zone of the neocortex, neocortical interneurons appear to he derived from the germinal zone of the basal ganglia. These interneurons follow a tangential migratory pathway from the ganglionic eminences to the cortex. Interneurons of the olfactory bulb follow a distinct tangential migration from the basal ganglia. The Dix homeobox genes, which are essential for basal ganglia differentiation, are also required for the development of neocortical and olfactory bulb interneurons. Furthermore, evidence is presented that retroviral-mediated expression of DLX2 in neocortical cells can induce GABAergic interneuron differentiation.