Disease relevance of Emx2

• A goal of this study was to use recombinant adenovirus (AdV) to ectopically express Emx2 in the embryonic neocortex as a gain-of-function approach to study its role in the area-specific targeting of thalamocortical axons (TCAs), using the rat as a model [1].

High impact information on Emx2

• The Emx2 expression domain is comprised of dorsal telencephalon and small diencephalic regions, both dorsally and ventrally [2].
• We previously cloned and characterized Emx1 and Emx2, two mouse genes related to empty spiracles that are expressed in restricted regions of the developing forebrain, including the presumptive cerebral cortex and olfactory bulbs [2].
• Regulation of area identity in the mammalian neocortex by Emx2 and Pax6 [3].
• Our results substantiate that COUP-TFI, an intrinsic factor, may work in concert with Pax6 and Emx2 to specify neocortical identity [4].
• Mammalian homeogenes of the Emx family, Emx1 and Emx2, are expressed in the developing cerebral cortex and are involved in the patterning of the rostral brain [5].

Biological context of Emx2

• Here we show that high-level expression of at least one functional allele of either of the homeobox genes Emx2 or Pax6 in the dorsal telencephalon is necessary and sufficient to stably activate morphogenesis of cerebral cortex and to repress that of adjacent structures, such as striatum [6].
• Molecular genetic studies implicate fibroblast growth factor 8 (FGF8), and the transcription factor Emx2, in development of the neocortical area map [7].
• Vax1 chromosomal location is mapped at the distal end of the mouse chromosome 19, linked with that of Emx2 [8].
• We previously demonstrated that the two homeobox genes Emx2 and Pax6 promote development of caudal-medial and rostral-lateral cortex, respectively, by properly shaping the early cortical protomap and possibly modulating the tangential growth ratio between medial and lateral cortical anlagen [9].
• Analysis of the phenotype of Emx2 null embryos has shown that this transcription factor plays important roles in neuroblast proliferation, migration and differentiation, as well as in the development of the diencephalon, where it has been shown to cooperate with Otx2 [10].

Anatomical context of Emx2

• Emx2 patterns the neocortex by regulating FGF positional signaling [7].
• Conversion of cerebral cortex into basal ganglia in Emx2(-/-) Pax6(Sey/Sey) double-mutant mice [6].
• Cortical size, lamination, thalamus, and thalamocortical pathfinding are normal in homozygous nestin-Emx2 mice [11].
• As expected for a transcription factor, Emx2 is present in the nucleus of immature and mature olfactory sensory neurons [12].
• Subcellular fractionations of olfactory bulb synaptosomes, combined with chemical lesions of olfactory neurons, confirm the presence of Emx2 in axon terminals [12].

Associations of Emx2 with chemical compounds

• Emx2 knockout mice appear to show a shift in the areal identity in the cerebral cortex , which is matched with altered distribution of thalamocortical projections (Bishop et al. [2000] Science 288:344-349; Mallamaci et al. [2000] Nat Neurosci. 3:679-686) [corrected] [13].
• We used carbocyanine dye tracing to visualize thalamocortical and corticofugal projections as well as immunohistochemistry for L1 and TAG-1, respective markers of the two axonal systems, in wild-type, heterozygote, and null mutant for Emx2 at embryonic (E) ages ranging from E13.5 to E18 [13].
• Finally, retinoic acid proximalizes both the level of Emx-2 expression and the positional memory of the blastema suggesting Emx-2 may participate in pattern formation by specifying positional information [14].

Regulatory relationships of Emx2

• In particular, Emx2 appears to be expressed exclusively in the germinal ventricular zone of the developing cerebral cortex [15].
• During early embryogenesis, Emx2 is expressed in the presumptive cerebral cortex and olfactory bulbs and later, in the hippocampus proper and dentate gyrus [16].
• At the same time, Emx2 is expressed in the epithelial components of the developing urogenital system and, in Emx2 mutant mice, the kidneys, ureters, gonads and genital tracts were completely missing [17].
• The vertebrate Emx genes are expressed in a nested pattern in early embryonic cerebral cortex, such that a medial strip of cortex expresses Emx2 but not Emx1 [18].

Other interactions of Emx2

• Here we report that Emx2, by regulating FGF8, has an indirect but vital role in area-map development [7].
• Finally, cortical domain shifts that characterize Emx2 mutants were rescued by sequestering excess FGF8 with a truncated FGF receptor construct [7].
• Finally Emx2 is very interesting from the evolutionary point of view, as it has been shown to share a high degree of homology in its sequence and function with Vax1, another homeobox gene regulating basal forebrain development [10].
• Loss of Emx2 function leads to ectopic expression of Wnt1 in the developing telencephalon and cortical dysplasia [19].
• In order to genetically determine the interaction between Emx and Otx genes in forebrain development, we have examined Emx2(-/-)Otx2(+/-) double mutants and Emx2 knock-in mutants into the Otx2 locus (Otx2(+/Emx2)) [20].

Analytical, diagnostic and therapeutic context of Emx2

• In order to better understand the role of Emx1 and Emx2 in the maturation of the cortex we analysed by in situ hybridization their expression patterns in the developing mouse cerebral cortex, from embryonic day 12.5 to adulthood [21].
• Increased expression of Emx2 reduced average implantation rate by approximately 40% (P = 0.00006) resulting in an average number of implanted embryos per litter of 13.7 in the control group to 8.2 in the pcDNA3.1/Emx2-treated group [22].
• Micromanipulation experiments revealed that ectoderm ablation over the somites does not affect Emx2 expression but inhibits the formation of the scapula blade indicating that Emx2 is not sufficient to induce scapula blade formation [23].
• Traced entorhinal afferents in co-cultures with hippocampus from embryonic Emx2-/- mice terminate diffusely in the prospective dentate gyrus in contrast to the layer-specific termination of co-cultures from wild-type littermates [24].
• Linkage mapping of Emx2 to mouse chromosome 19 [25].

References