Distinctcis-Regulatory Elements from theDlx1/Dlx2Locus Mark Different Progenitor Cell Populations in the Ganglionic Eminences and Different Subtypes of Adult Cortical Interneurons

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Abstract
Distinct subtypes of cortical GABAergic interneurons provide inhibitory signals that are indispensable for neural network function. TheDlxhomeobox genes have a central role in regulating their development and function. We have characterized the activity of threecis-regulatory sequences involved in forebrain expression of vertebrateDlxgenes: upstream regulatory element 2 (URE2), I12b, and I56i. The three regulatory elements display regional and temporal differences in their activities within the lateral ganglionic eminence (LGE), medial ganglionic eminence (MGE), and caudal ganglionic eminence (CGE) and label distinct populations of tangentially migrating neurons at embryonic day 12.5 (E12.5) and E13.5. We provide evidence that the dorsomedial and ventral MGE are distinct sources of tangentially migrating neurons during midgestation. In the adult cortex, URE2 and I12b/I56i are differentially expressed in parvalbumin-, calretinin-, neuropeptide Y-, and neuronal nitric oxide synthase-positive interneurons; I12b and I56i were specifically active in somatostatin-, vasoactive intestinal peptide-, and calbindin-positive interneurons. These data suggest that interneuron subtypes use distinct combinations ofDlx1/Dlx2enhancers from the time they are specified through adulthood.