Figure 1.

Embryonic origin and mature fates of cortical interneurons. (a) Schematic showing the subdivisions of the embryonic telencephalon. The three regions where cortical and hippocampal interneurons originate are the medial ganglionic eminence (MGE) (including the dorsal MGE-dMGE), the caudal ganglionic eminence (CGE) and the preoptic area (POA). The dorsal part of the CGE (dCGE) is a caudal extension of the lateral ganglionic eminence (LGE) and is distinct from the MGE. These progenitor zones of the telencephalon can be identified by combinatorial expression of transcription factors within the neuroepithelium. (b) The major classes of cortical interneurons that originate from the three neuroepithelial regions during embryogenesis can be identified using neurochemical markers. The MGE generates 60% of all cortical interneurons and includes mainly parvalbumin (PV)-expressing and somatostatin (SST)-expressing subtypes. A large fraction of the SST cells co-express reelin (RLN). SST/calretinin (CR) co-expressing interneurons are derived exclusively from the dMGE. The POA generates ∼10% of all cortical interneurons and includes a variety of subtypes. The dCGE is the source of ∼30% of all cortical interneurons. Half of these co-express RLN and smaller fractions express vasoactive intestinal peptide (VIP) and/or CR. Note that neuropeptide Y (not shown in the figure) is also expressed in subsets of cortical interneurons, including ones derived from the POA. (c) Distribution of MGE (red)-derived, POA (blue)-derived and dCGE (green)-derived interneuron populations within the different layers (I–VI) of the adult cortex.