Cortical excitatory neurons and glia, but not GABAergic neurons, are produced in the Emx1-expressing lineage

Abstract

By homologous recombination of an internal ribosome entry site and Cre recombinase coding region into the 3'-untranslated region of the mouse Emx1 gene, we have generated a strain of mice, Emx1(IRES)cre, that expresses the Cre recombinase in a spatial and temporal pattern like that observed for Emx1. When mated to reporter strains, these mice are a sensitive means to fate-map the Emx1-expressing cells of the developing forebrain. Our results demonstrate that radial glia, Cajal-Retzius cells, glutamatergic neurons, astrocytes, and oligodendrocytes of most pallial structures originate from an Emx1-expressing lineage. On the other hand, most of the pallial GABAergic neurons arise outside the Emx1-expressing lineage. Structures that are located near the basal ganglia (e.g., the amygdala and endopiriform nuclei) are not uniformly derived from Emx1-expressing cells.

Fig. 1.

Tissue-specific lox recombination driven by Emx1^IREScre.A, Schematic of the Emx1^IREScretargeting construct. SA, Splice acceptor;UGA, stop codon; pA, polyadenylation signal; black triangles, FRT sites; small arrow, PGK promoter. B, Schematic of Emx1 exon 3. Hatched box, Coding region; open box, 3′-untranslated. C, Western blots of cortical protein from wild-type mice (lanes 1,2) and Emx1^IREScre/Emx1^IREScremice (lanes 3, 4), probed with anti-Emx1 or anti-NeuN. D, An X-galstained E10.5 Emx1^IREScre;R26R embryo. E, An E10.5 Emx1^IREScre;R26R embryo X-gal stained and processed for neurofilament immunohistochemistry. Cranial ganglia are numbered.F–I, Sections (10 μm) of X-gal-stained E12.5 Emx1^IREScre;R26R embryos. AEP, Anterior entopeduncular area;amyg, amygdala; ch, choroid plexus primordium; DP, dorsal pallium; EMT, eminentia thalami; hem, cortical hem;MGE, medial ganglionic eminence; MP, medial pallium; LGE, lateral ganglionic eminence;LP, lateral pallium; POA, preoptic area;OT, olfactory tuberculum; pspb, pallial–subpallial boundary; Sp, pallial septum;Ssp, subpallial septum; VP, ventral pallium. Also see supplemental material athttp://www.jneurosci.org.

Fig. 2.

Recombination in the adult Emx1^IREScre;R26R brain. A–F, Coronal sections (40 μm) of X-gal-stained adult Emx1^IREScre;R26R brain. AA, Anterior amygdaloid area; ac, anterior commissure; ACo, anterior cortical amygdaloid nucleus; AHip, amygdalohippocampal area;BL, basolateral amygdala; BM, basomedial amygdala; Bst, bed nucleus of stria terminalis;C, central amygala; cc, corpus callosum;ch, choroid plexus; Cing.Cx, cingulate cortex; CLdl, dorsolateral claustrum;CLvm, ventromedial claustrum; CxA, cortex–amygdala transition zone; DP, dorsal pallidum;DTT, dorsal tenia tectum; EPd, dorsal endopiriform nucleus; EPv, ventral endopiriform nucleus;ERCx, ectorhinal cortex; f, fimbria;Hy, hypothalamus; L, lateral amygdala;LP, lateral pallidum; LSD, lateral septal nucleus dorsal; LSI, intermediate lateral septal nucleus; M, medial amygdala; MS, medial septum; NAOT, bed nucleus of the accessory olfactory tract; NLOT (2), nucleus of lateral olfactory tract, layer II;Pal, pallidum; PCol,posterolateral cortical amygdaloid nucleus; PCom, posteromedial amygdaloid nucleus; PirCx, piriform cortex;PLd, paralamboid septal nucleus dorsal; St, striatum; Th, thalamus; VP, ventral pallidum;VTT, ventral tenia tectum. Also see supplemental material athttp://www.jneurosci.org.

Fig. 3.

Interneurons originate outside the Emx1 lineage.A–C, Adult Emx1^IREScre;R26R visual cortex probed with anti-β-Gal and anti-GABA.D–F, E12.5 Emx1^IREScre;R26R pallium probed with anti-calbindin anti-β-Gal.G–L, Adult Emx1^IREScre;R26R striatum, probed with anti-β-Gal and the other antibodies indicated. All sections are 10 μm coronal. Arrows indicate double-labeled cells.

Fig. 4.

Cajal-Retzius cells, astrocytes, and oligodendrocytes. A–F, Retrosplenial cortex (A–C) and visual cortex (D–F) of P4 Emx1^IREScre;R26R mice probed with anti-calretinin and anti-β-Gal.G–I, E12.5 Emx^IREScre;R26R cortical plate probed with anti-RC2 and anti-β-Gal.Asterisk indicates nucleus.J–L, Cultured Emx1^IREScre;R26R astrocytes probed with anti-β-Gal and anti-S-100.M–O, X-gal-stained adult Emx1^IREScre;R26R corpus callosum (M), fimbria (N), and anterior commissure (O). P–U, Emx1^IREScre;R26R (P–R) and Emx1^IREScre;Z/AP (S–U) corpus callosum probed with anti-β-Gal and anti-Rip. S, Arrow indicates blood vessel. V, Adult Emx1^IREScre;Z/AP neocortex. Blood vessels and scattered cells (arrows) are X-gal stained.