A wide diversity of cortical GABAergic interneurons derives from the embryonic preoptic area

GABA-containing (GABAergic) interneurons comprise a very heterogeneousgroupof cells that are crucial for cortical function. Different classes of interneurons specialize in targeting specific subcellular domains of excitatory pyramidal cells or other interneurons, which provides cortical circuits with an enormous capability for information processing. As in other regions of the CNS, cortical interneuron diversity is thought to emerge from the genetic specification of different groups of progenitor cells within the subpallium. Most cortical interneurons originate from twomainregions, the medial and the caudal ganglionic eminences(MGEand CGE, respectively). In addition, it has beenshownthat progenitors in the embryonic preoptic area (POA) also produce a small population of cortical GABAergic interneurons. Here, we show that the contribution of the POA to the complement of cortical GABAergic interneurons is larger than previously believed. Using genetic fate mapping and in utero transplantation experiments, we demonstrate that Dbx1-expressing progenitor cells in the POA give rise to a small but highly diverse cohort of cortical interneurons, with some neurochemical and electrophysiological characteristics that were previously attributed to MGE- or CGEderived interneurons. There are, however, some features that seem to distinguish POA-derived interneurons from MGE- or CGE-derived cells, such as their preferential laminar location. These results indicate that themechanismscontrolling the specification of different classes of cortical interneurons might be more complex than previously expected. Together with earlier findings, our results also suggest that the POA generates nearly 10% of the GABAergic interneurons in the cerebral cortex of the mouse.