Specific glial populations regulate hippocampal morphogenesis

The hippocampus plays an integral role in spatial navigation, learning and memory, and is a major site for adult neurogenesis. Critical to these functions is the proper organization of the hippocampus during development. Radial glia are known to regulate hippocampal formation, but their precise function in this process is yet to be defined. We find that in Nuclear Factor I b (Nfib)-deficient mice, a subpopulation of glia from the ammonic neuroepithelium of the hippocampus fail to develop. This results in severe morphological defects, including a failure of the hippocampal fissure, and subsequently the dentate gyrus, to form. As in wild-type mice, immature nestin-positive glia, which encompass all types of radial glia, populate the hippocampus in Nfib-deficient mice at embryonic day 15. However, these fail to mature into GLAST- and GFAP-positive glia, and the supragranular glial bundle is absent. In contrast, the fimbrial glial bundle forms, but alone is insufficient for proper hippocampal morphogenesis. Dentate granule neurons are present in the mutant hippocampus but their migration is aberrant, likely resulting from the lack of the complete radial glial scaffold usually provided by both glial bundles. These data demonstrate a role for Nfib in hippocampal fissure and dentate gyrus formation, and that distinct glial bundles are critical for correct hippocampal morphogenesis

Gene expression signature of cerebellar hypoplasia in a mouse model of Down syndrome during postnatal development

Background Down syndrome is a chromosomal disorder caused by the presence of three copies of chromosome 21. The mechanisms by which this aneuploidy produces the complex and variable phenotype observed in people with Down syndrome are still under discussion. Recent studies have demonstrated an increased transcript level of the three-copy genes with some dosage compensation or amplification for a subset of them. The impact of this gene dosage effect on the whole transcriptome is still debated and longitudinal studies assessing the variability among samples, tissues and developmental stages are needed. Results We thus designed a large scale gene expression study in mice (the Ts1Cje Down syndrome mouse model) in which we could measure the effects of trisomy 21 on a large number of samples (74 in total) in a tissue that is affected in Down syndrome (the cerebellum) and where we could quantify the defect during postnatal development in order to correlate gene expression changes to the phenotype observed. Statistical analysis of microarray data revealed a major gene dosage effect: for the three-copy genes as well as for a 2 Mb segment from mouse chromosome 12 that we show for the first time as being deleted in the Ts1Cje mice. This gene dosage effect impacts moderately on the expression of euploid genes (2.4 to 7.5% differentially expressed). Only 13 genes were significantly dysregulated in Ts1Cje mice at all four postnatal development stages studied from birth to 10 days after birth, and among them are 6 three-copy genes. The decrease in granule cell proliferation demonstrated in newborn Ts1Cje cerebellum was correlated with a major gene dosage effect on the transcriptome in dissected cerebellar external granule cell layer. Conclusion High throughput gene expression analysis in the cerebellum of a large number of samples of Ts1Cje and euploid mice has revealed a prevailing gene dosage effect on triplicated genes. Moreover using an enriched cell population that is thought responsible for the cerebellar hypoplasia in Down syndrome, a global destabilization of gene expression was not detected. Altogether these results strongly suggest that the three-copy genes are directly responsible for the phenotype present in cerebellum. We provide here a short list of candidate genes

NFIA controls telencephalic progenitor cell differentiation through repression of the Notch effector Hes1

The balance between self-renewal and differentiation of neural progenitor cells is an absolute requirement for the correct formation of the nervous system. Much is known about both the pathways involved in progenitor cell self-renewal, such as Notch signaling, and the expression of genes that initiate progenitor differentiation. However, whether these fundamental processes are mechanistically linked, and specifically how repression of progenitor self-renewal pathways occurs, is poorly understood. Nuclear factor I A (Nfia), a gene known to regulate spinal cord and neocortical development, has recently been implicated as acting downstream of Notch to initiate the expression of astrocyte-specific genes within the cortex. Here we demonstrate that, in addition to activating the expression of astrocyte-specific genes, Nfia also downregulates the activity of the Notch signaling pathway via repression of the key Notch effector Hes1. These data provide a significant conceptual advance in our understanding of neural progenitor differentiation, revealing that a single transcription factor can control both the activation of differentiation genes and the repression of the self-renewal genes, thereby acting as a pivotal regulator of the balance between progenitor and differentiated cell states

Loss of neuronal potassium/chloride cotransporter 3 (KCC3) is responsible for the degenerative phenotype in a conditional mouse model of hereditary motor and sensory neuropathy associated with agenesis of the corpus callosum

Disruption of the potassium/chloride cotransporter 3 (KCC3), encoded by the SLC12A6 gene, causes hereditary motor and sensory neuropathy associated with agenesis of the corpus callosum (HMSN/ACC), a neurodevelopmental and neurodegenerative disorder affecting both the peripheral nervous system and CNS. However, the precise role of KCC3 in the maintenance of ion homeostasis in the nervous system and the pathogenic mechanisms leading to HMSN/ACC remain unclear. We established two Slc12a6 Cre/LoxP transgenic mouse lines expressing C-terminal truncated KCC3 in either a neuron-specific or ubiquitous fashion. Our results suggest that neuronal KCC3 expression is crucial for axon volume control. We also demonstrate that the neuropathic features of HMSN/ACC are predominantly due to a neuronal KCC3 deficit, while the auditory impairment is due to loss of non-neuronal KCC3 expression. Furthermore, we demonstrate that KCC3 plays an essential role in inflammatory pain pathways. Finally, we observed hypoplasia of the corpus callosum in both mouse mutants and a marked decrease in axonal tracts serving the auditory cortex in only the general deletion mutant. Together, these results establish KCC3 as an important player in both central and peripheral nervous system maintenance

Visualization of mouse barrel cortex using ex-vivo track density imaging

We describe the visualization of the barrel cortex of the primary somatosensory area (S1) of ex vivo adult mouse brain with short-tracks track density imaging (stTDI). stTDI produced much higher definition of barrel structures than conventional fractional anisotropy (FA), directionally-encoded color FA maps, spin-echo and T2-weighted imaging and gradient echo Ti/T2*-weighted imaging. 3D high angular resolution diffusion imaging (HARDI) data were acquired at 48 micron isotropic resolution for a (3 mm)3 block of cortex containing the barrel field and reconstructed using stTDI at 10 micron isotropic resolution. HARDI data were also acquired at 100 micron isotropic resolution to image the whole brain and reconstructed using stTDI at 20 micron isotropic resolution. The 10 micron resolution stTDI maps showed exceptionally clear delineation of barrel structures. Individual barrels could also be distinguished in the 20 micron stTDI maps but the septa separating the individual barrels appeared thicker compared to the 10 micron maps, indicating that the ability of stTDI to produce high quality structural delineation is dependent upon acquisition resolution. Close homology was observed between the barrel structure delineated using stTDI and reconstructed histological data from the same samples. stTDI also detects barrel deletions in the posterior medial barrel sub-field in mice with infraorbital nerve cuts. The results demonstrate that stTDI is a novel imaging technique that enables three-dimensional characterization of complex structures such as the barrels in S1 and provides an important complementary non-invasive imaging tool for studying synaptic connectivity, development and plasticity of the sensory system. (C) 2013 Elsevier Inc. All rights reserved

Functional roles of group II metabotropic glutamate receptors in injury and epilepsy

Abstract not availabl

Functional roles of group II metabotropic glutamate receptors in injury and epilepsy

Abstract not availabl

Excitotoxic injury profiles of low-affinity kainate receptor agonists in cortical neuronal cultures

Neurotoxic profiles of putative agonists for low-affinity kainate subtypes of Image -glutamate receptors (GluR5-7) were determined in cultured cortical neurones. Rank order of neurotoxic potency (μM): (S)-5-iodowillardiine (9)≈(2S,4R,6E)-2-amino-4-carboxy-7-(2-naphthyl)hept-6-enoic acid (LY339434, 11)>(2S,4R)-4-methylglutamate (33)>kainate (100)>(RS)-2-amino-3-(hydroxy-5-tert-butylisoxazol-4-yl)propanoic acid (ATPA, 360). Using ionotropic glutamate receptor antagonists, neurotoxicity induced by kainate, ATPA and (S)-5-iodowillardiine appeared to involve a GluR5-7 component, unlike LY339434 and (2S,4R)-4-methylglutamate. These putative GluR5-7 agonists exhibited complex excitotoxic profiles highlighting the importance of studying native glutamate receptors

Down syndrome gene dosage imbalance on cerebellum development

Down syndrome (DS) is a chromosomal disorder whereby genes on chromosome 21 are present in three copies. This gene copy imbalance is thought to be responsible for a number of debilitating conditions experienced by individuals with DS. Amongst these is a reduced cerebellar volume, or cerebellar hypoplasia, which is believed to contribute to the perturbation of fine motor control. Mouse models of DS (such as Ts65Dn, Ts1Cje, Tc1) exhibit a cerebellar phenotype similar to that of individuals with DS and which primarily manifests as a disruption of the density of the granule cell layer. Dissecting which of the three-copy genes are responsible for this phenotype (the primary gene dosage effect) has been a task undertaken by researchers working with various segmental trisomies and transgenic mice. It is generally agreed that, when expressed, three-copy genes of trisomic mice are expressed at around 1.5 times that of the same genes in euploid (wild-type) mice. However, amongst these studies there does not appear to be a consensus on the nature and extent of differential expression of two-copy genes in trisomic mice—the secondary dosage effect. Much of this variation may have to do with the stage of development investigated and the nature and complexity of the tissue (i.e. whole brain versus the cerebellum). The recent discovery that trisomic granule cell precursors are less sensitive to sonic hedgehog-induced proliferation has opened up another avenue for the identification of three-copy genes responsible for the cerebellar phenotype. It is hoped that further investigation of this phenomenon, together with new mouse segmental trisomies and transgenics, will reveal the cause of the proliferation deficit and allow for potential treatment

Excitotoxic profile of LY339434, a GluR5 agonist, in cultured murine cortical neurons

The neurotoxic profile of (2S,4R,6E)-2-amino-4-carboxy-7-(2-naphthyl)hept-6-enoic acid (LY339434), a low-affinity kainate receptor subtype 5 (GluR5) agonist at recombinant human glutamate receptors, was evaluated to investigate the involvement of GluR5 in excitotoxic neuronal death. Murine cortical neurons were exposed to treatments for 24 h and assessed by a cell viability assay and phase-contrast microscopy. LY339434 (1-1000 mu M) caused a concentration-dependent decrease in cell viability (EC50 = 11.4+/-1.2 mu M) that was only attenuated by (5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5, 10-imine (MK-801, 10 mu M), but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX; 50 mu M) or 1-(4-aminophenyl)-4-methyl-7,8-methylenedioxy-5H-2,3-benzodiazepine (GYKI 52466, 20 mu M). Labeling with nucleic acid binding dyes revealed that LY339434 induced few apoptotic-like characteristics. These findings indicate that in cultured murine cortical neurons, LY339434 acts predominantly through N-methyl-D-aspartate (NMDA) receptors rather than GluR5 to effect neuronal death that is rapid and involves predominantly necrosis rather than morphological apoptosis. (C) 2000 Elsevier Science B.V. All rights reserved