Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0004134 (ataxia)
 15,886 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Inherited forms of ataxia and absence seizures in mice have been linked to defects in voltage-dependent calcium channel subunits. However, a correlation between the sites of neuronal dysfunction and the impact of the primary lesion upon calcium channel subunit expression or function has not been clearly established. For example, the mutation in stargazer mice has pleiotropic consequences including synaptic alterations in cerebellar granule cells, hippocampal CA3/mossy fibers, and cortical neurons in layer V that, presumably, lead to ataxia and seizures. Genetic analysis of stargazer mice determined that the defective gene encodes a protein expressed in brain (gamma2) with limited homology to the skeletal muscle L-type calcium channel gamma1 subunit. Although additional gamma isoforms have been subsequently identified primarily in neural tissue, little was known about the proteins they encode. Therefore, this study explored the distribution and biochemical properties of gamma2 and other gamma isoforms in wild-type and stargazer brain. We cloned human gamma2, gamma3, and gamma4 isoforms, produced specific anti-peptide antibodies to gamma isoforms and characterized both heterologously expressed and endogenous gamma. We identified regional specificity in the expression of gamma isoforms by western analysis and immunohistochemistry. We report for the first time that the mutation in the stargazer gene resulted in the loss of gamma2 protein. Furthermore, no compensatory changes in the expression of gamma3 or gamma4 protein were evident in stargazer brain. In contrast to other voltage-dependent calcium channel subunits, gamma immunostaining was striking in that it was primarily detected in regions highly enriched in excitatory glutamatergic synapses and faintly detected in cell bodies, suggesting a role for gamma in synaptic functions. Sites of known synaptic dysfunction in stargazer (the hippocampal CA3 region, dentate gyrus, and cerebellar molecular layer) were revealed as relying primarily upon gamma2, as total gamma isoform expression was dramatically decreased in these regions. Electron microscopy localized anti-gamma antibody immunostaining to dendritic structures of hippocampal mossy fiber synapses, with enrichment at postsynaptic densities. To assess the association of native gamma with voltage-dependent calcium channel or alpha-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) receptor subunits, gamma isoforms (gamma2, gamma3 and gamma4) were detergent solubilized from mouse forebrain. Antibodies against a highly conserved C-terminal epitope present in gamma2, gamma3 and gamma4 immunoprecipitated voltage-dependent calcium channel subunits (alpha1B), providing the first in vivo evidence that gamma and voltage-dependent calcium channels form stable complexes. Furthermore, both anti-gamma2 antibodies and anti-alpha1B antibodies independently immunoprecipitated the AMPA receptor subunit, GluR1, from mouse forebrain homogenates. In summary, loss of gamma2 immunoreactivity in stargazer is precisely localized so as to contribute to previously characterized synaptic defects. The data in this paper provide compelling evidence that gamma isoforms form complexes in vivo with voltage-dependent calcium channels as well as AMPA receptors, are selectively and differentially expressed in neuronal processes, and localize primarily to dendritic structures in the hippocampal mossy fiber region.
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PMID:Biochemical and anatomical evidence for specialized voltage-dependent calcium channel gamma isoform expression in the epileptic and ataxic mouse, stargazer. 1151 27

Nova is a neuron-specific RNA binding protein targeted in patients with the autoimmune disorder paraneoplastic opsoclonus-myoclonus ataxia, which is characterized by failure of inhibition of brainstem and spinal motor systems. Here, we have biochemically confirmed the observation that splicing regulation of the inhibitory GABA(A) receptor gamma2 (GABA(A)Rgamma2) subunit pre-mRNA exon E9 is disrupted in mice lacking Nova-1. To elucidate the mechanism by which Nova-1 regulates GABA(A)Rgamma2 alternative splicing, we systematically screened minigenes derived from the GABA(A)Rgamma2 and human beta-globin genes for their ability to support Nova-dependent splicing in transient transfection assays. These studies demonstrate that Nova-1 acts directly on GABA(A)Rgamma2 pre-mRNA to regulate E9 splicing and identify an intronic region that is necessary and sufficient for Nova-dependent enhancement of exon inclusion, which we term the NISE (Nova-dependent intronic splicing enhancer) element. The NISE element (located 80 nucleotides upstream of the splice acceptor site of the downstream exon E10) is composed of repeats of the sequence YCAY, consistent with previous studies of the mechanism by which Nova binds RNA. Mutation of these repeats abolishes binding of Nova-1 to the RNA in vitro and Nova-dependent splicing regulation in vivo. These data provide a molecular basis for understanding Nova regulation of GABA(A)Rgamma2 alternative splicing and suggest that general dysregulation of Nova's splicing enhancer function may underlie the neurologic defects seen in Nova's absence.
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PMID:Nova regulates GABA(A) receptor gamma2 alternative splicing via a distal downstream UCAU-rich intronic splicing enhancer. 1280 7

The voltage-dependent calcium channel gamma4 subunit protein, CACNG4, is closely related to the gamma2 subunit, CACNG2. Both are expressed primarily in the brain and share 53% amino acid identity. The Cacng2 gene is disrupted in the stargazer mouse, with its distinctive phenotype including ataxia, frequent absence seizure episodes, and head elevation. A disruption within Cacng4 was engineered to assess its particular function. The homozygous Cacng4-targeted mutant mouse appeared normal with no ataxic gait or absence seizures, suggesting that other members of the gamma subunit family might functionally compensate for the absence of CACNG4. To test this hypothesis, the targeted Cacng4 mutation was combined with alleles of Cacng2. Absence seizures were observed in combination with the stargazer 3J mutation, which itself does not have seizures, and increased seizure activity was observed in combination with the waggler allele. Furthermore, within the corticothalamic loop, where absence seizures arise, CACNG4 expression is restricted to the thalamus. Our studies show that the CACNG4 protein has seizure suppressing activity, but this effect is revealed only when CACNG2 expression is also compromised, suggesting that CACNG subunits have in vivo overlapping functions.
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PMID:A targeted mutation in Cacng4 exacerbates spike-wave seizures in stargazer (Cacng2) mice. 1567 29

The Tottering (cacna1a(tg)) mouse arose as a consequence of a spontaneous mutation in cacna1a, the gene encoding the pore-forming subunit of the pre-synaptic P/Q-type voltage-gated calcium channel (VGCC, Ca(V)2.1). The mouse phenotype includes ataxia and intermittent myoclonic seizures which have been attributed to impaired excitatory neurotransmission at cerebellar granule cell (CGC) parallel fiber-Purkinje cell (PF-PC) synapses [Zhou YD, Turner TJ, Dunlap K (2003) Enhanced G-protein-dependent modulation of excitatory synaptic transmission in the cerebellum of the Ca(2+)-channel mutant mouse, tottering. J Physiol 547:497-507]. We hypothesized that the expression of cerebellar GABA(A) receptors may be affected by the mutation. Indeed, abnormal GABA(A) receptor function and expression in the cacna1a(tg) forebrain has been reported previously [Tehrani MH, Barnes EM Jr (1995) Reduced function of gamma-aminobutyric acid A receptors in tottering mouse brain: role of cAMP-dependent protein kinase. Epilepsy Res 22:13-21; Tehrani MH, Baumgartner BJ, Liu SC, Barnes EM Jr (1997) Aberrant expression of GABA(A) receptor subunits in the tottering mouse: an animal model for absence seizures. Epilepsy Res 28:213-223]. Here we show a deficit of 40.2+/-3.6% in the total number of cerebellar GABA(A) receptors expressed (gamma2+delta subtypes) in adult cacna1a(tg) relative to controls. [(3)H]Muscimol autoradiography identified that this was partly due to a significant loss of CGC-specific alpha6 subunit-containing GABA(A) receptor subtypes. A large proportion of this loss of alpha6 receptors was attributable to a significantly reduced expression of the CGC-specific benzodiazepine-insensitive Ro15-4513 (BZ-IS) binding subtype, alpha6betagamma2 subunit-containing receptors. BZ-IS binding was reduced by 36.6+/-2.6% relative to controls in cerebellar membrane homogenates and by 37.2+/-3.7% in cerebellar sections. Quantitative immunoblotting revealed that the steady-state expression level of alpha6 and gamma2 subunits was selectively reduced relative to controls by 30.2+/-8.2% and 38.8+/-13.1%, respectively, alpha1, beta3 and delta were unaffected. Immunohistochemically probed control and cacna1a(tg) cerebellar sections verified that alpha6 and gamma2 subunit expression was reduced and that this deficit was restricted to the CGC layer. Thus, we have shown that abnormal cerebellar P/Q-type VGCC activity results in a deficit of CGC-specific subtype(s) of GABA(A) receptors which may contribute to, or may be a consequence of the impaired cerebellar network signaling that occurs in cacna1a(tg) mice.
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PMID:Aberrant cerebellar granule cell-specific GABAA receptor expression in the epileptic and ataxic mouse mutant, Tottering. 1761 9

Although GABA(A) receptor-mediated inhibition of cerebellar Purkinje cells by molecular layer interneurons (MLIs) has been studied intensely at the cellular level, it has remained unclear how this inhibition regulates cerebellum-dependent behaviour. We have implemented two complementary approaches to investigate the function of the MLI-Purkinje cell synapse on the behavioural level. In the first approach we permanently disrupted inhibitory fast synaptic transmission at the synapse by genetically removing the postsynaptic GABA(A) receptors from Purkinje cells (PC-Deltagamma2 mice). We found that chronic disruption of the MLI-Purkinje cell synapse strongly impaired cerebellar learning of the vestibular occular reflex (VOR), presumably by disrupting the temporal patterns of Purkinje cell activity. However, in PC-Deltagamma2 mice the baseline VOR reflex was only mildly affected; indeed PC-Deltagamma2 mice show no ataxia or gait abnormalities, suggesting that MLI control of Purkinje cell activity is either not involved in ongoing motor tasks or that the system compensates for its loss. To investigate the latter possibility we developed an alternative genetic technique; we made the MLI-Purkinje cell synapse selectively sensitive to rapid manipulation with the GABA(A) receptor modulator zolpidem (PC-gamma2-swap mice). Minutes after intraperitoneal zolpidem injection, these PC-gamma2-swap mice developed severe motor abnormalities, revealing a substantial contribution of the MLI-Purkinje cell synapses to real time motor control. The cell-type selective permanent knockout of synaptic GABAergic input and the fast reversible modulation of GABAergic input at the same synapse illustrate how pursuing both strategies gives a fuller view.
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PMID:Studying Cerebellar Circuits by Remote Control of Selected Neuronal Types with GABA(A) Receptors. 2007 63