Publications by authors named "Emma Perkins"

20 Publications

  • Page 1 of 1

Altered network properties in C9ORF72 repeat expansion cortical neurons are due to synaptic dysfunction.

Mol Neurodegener 2021 Mar 4;16(1):13. Epub 2021 Mar 4.

Euan MacDonald Centre for MND Research, University of Edinburgh, Edinburgh, EH16 4SB, UK.

Background: Physiological disturbances in cortical network excitability and plasticity are established and widespread in amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients, including those harbouring the C9ORF72 repeat expansion (C9ORF72) mutation - the most common genetic impairment causal to ALS and FTD. Noting that perturbations in cortical function are evidenced pre-symptomatically, and that the cortex is associated with widespread pathology, cortical dysfunction is thought to be an early driver of neurodegenerative disease progression. However, our understanding of how altered network function manifests at the cellular and molecular level is not clear.

Methods: To address this we have generated cortical neurons from patient-derived iPSCs harbouring C9ORF72 mutations, as well as from their isogenic expansion-corrected controls. We have established a model of network activity in these neurons using multi-electrode array electrophysiology. We have then mechanistically examined the physiological processes underpinning network dysfunction using a combination of patch-clamp electrophysiology, immunocytochemistry, pharmacology and transcriptomic profiling.

Results: We find that C9ORF72 causes elevated network burst activity, associated with enhanced synaptic input, yet lower burst duration, attributable to impaired pre-synaptic vesicle dynamics. We also show that the C9ORF72 is associated with impaired synaptic plasticity. Moreover, RNA-seq analysis revealed dysregulated molecular pathways impacting on synaptic function. All molecular, cellular and network deficits are rescued by CRISPR/Cas9 correction of C9ORF72. Our study provides a mechanistic view of the early dysregulated processes that underpin cortical network dysfunction in ALS-FTD.

Conclusion: These findings suggest synaptic pathophysiology is widespread in ALS-FTD and has an early and fundamental role in driving altered network function that is thought to contribute to neurodegenerative processes in these patients. The overall importance is the identification of previously unidentified defects in pre and postsynaptic compartments affecting synaptic plasticity, synaptic vesicle stores, and network propagation, which directly impact upon cortical function.
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http://dx.doi.org/10.1186/s13024-021-00433-8DOI Listing
March 2021

Generation of pure monocultures of human microglia-like cells from induced pluripotent stem cells.

Stem Cell Res 2020 12 14;49:102046. Epub 2020 Oct 14.

Centre for Clinical Brain Sciences, University of Edinburgh, Edinburgh, UK; UK Dementia Research Institute at University of Edinburgh, Edinburgh, UK; Department of Neuropsychiatry and Laboratory of Molecular Psychiatry, Charité, Universitätsmedizin Berlin, BIH and DZNE, Berlin, Germany. Electronic address:

Microglia are resident tissue macrophages of the central nervous system (CNS) that arise from erythromyeloid progenitors during embryonic development. They play essential roles in CNS development, homeostasis and response to disease. Since microglia are difficult to procure from the human brain, several protocols have been developed to generate microglia-like cells from human induced pluripotent stem cells (hiPSCs). However, some concerns remain over the purity and quality of in vitro generated microglia. Here, we describe a new protocol that does not require co-culture with neural cells and yields cultures of 100% P2Y 95% TMEM119 ramified human microglia-like cells (hiPSC-MG). In the presence of neural precursor cell-conditioned media, hiPSC-MG expressed high levels of human microglia signature genes, including SALL1, CSF1R, P2RY12, TMEM119, TREM2, HEXB and SIGLEC11, as revealed by whole-transcriptome analysis. Stimulation of hiPSC-MG with lipopolysaccharide resulted in downregulation of P2Y expression, induction of IL1B mRNA expression and increase in cell capacitance. HiPSC-MG were phagocytically active and maintained their cell identity after transplantation into murine brain slices and human brain spheroids. Together, our new protocol for the generation of microglia-like cells from human iPSCs will facilitate the study of human microglial function in health and disease.
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http://dx.doi.org/10.1016/j.scr.2020.102046DOI Listing
December 2020

Smartphone use and perceptions of their benefit and detriment within Australian anaesthetic practice.

Anaesth Intensive Care 2020 Sep 6;48(5):366-372. Epub 2020 Oct 6.

Central Clinical School, Monash University, Melbourne, Australia.

The primary aim of this study was to evaluate the perceptions of Australian anaesthetists in relation to smartphone use within anaesthetic practice. In particular, we aimed to assess the frequency of smartphone use, the types and number of smartphone applications used, how reliant anaesthetists perceive themselves to be on smartphones and whether they perceive them to be a factor that aids or distracts from their practice. Secondly, we assessed whether there is an association between the type, frequency, reliance and perceptions of smartphone use and the years of experience as an anaesthetist. A 24-item questionnaire addressing these questions was created and distributed to an email list of credentialled anaesthetists in Melbourne, Australia. A total of 113 consultant anaesthetists who practise at 55 hospitals in Melbourne completed the questionnaire. Our results suggest that the majority of anaesthetists are using smartphones regularly in their practice. About 74% of respondents agreed that they rely on their smartphone for their work. We found that respondents were more likely to rely on smartphones and consider them to aid patient safety than to consider them a distraction. This phenomenon was particularly apparent in those who had been a consultant anaesthetist for less than three years. Furthermore, those who had been a consultant anaesthetist for less than three years were more likely to have more smartphone apps relating to anaesthetics, use them more often and rely on them to a greater degree. Our results highlight the ubiquitous and perceived useful nature of smartphones in anaesthetic practice.
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http://dx.doi.org/10.1177/0310057X20947427DOI Listing
September 2020

Epidemiology and clinical features of emergency department patients with suspected and confirmed COVID-19: A multisite report from the COVID-19 Emergency Department Quality Improvement Project for July 2020 (COVED-3).

Emerg Med Australas 2021 02 19;33(1):114-124. Epub 2020 Oct 19.

Emergency and Trauma Centre, Alfred Health, Melbourne, Victoria, Australia.

Objective: The aim of the present study was to describe the epidemiology and clinical features of patients presenting to the ED with suspected and confirmed COVID-19.

Methods: The COVID-19 ED (COVED) Project is an ongoing prospective cohort study in Australian EDs. This analysis presents data from eight sites across Victoria and Tasmania for July 2020 (during Australia's 'second wave'). All adult patients who met criteria for 'suspected COVID-19' and underwent testing for SARS-CoV-2 in the ED were eligible for inclusion. Study outcomes included a positive SARS-CoV-2 test result and mechanical ventilation.

Results: In the period 1 July to 31 July 2020, there were 30 378 presentations to the participating EDs and 2917 (9.6%; 95% confidence interval 9.3-9.9) underwent testing for SARS-CoV-2. Of these, 50 (2%) patients returned a positive result. Among positive cases, two (4%) received mechanical ventilation during their hospital admission compared to 45 (2%) of the SARS-CoV-2 negative patients (odds ratio 1.7, 95% confidence interval 0.4-7.3; P = 0.47). Two (4%) SARS-CoV-2 positive patients died in hospital compared to 46 (2%) of the SARS-CoV-2 negative patients (odds ratio 1.7, 95% confidence interval 0.4-7.1; P = 0.49). Strong clinical predictors of a positive SARS-CoV-2 result included self-reported fever, non-smoking status, bilateral infiltrates on chest X-ray and absence of a leucocytosis on first ED blood tests (P < 0.05).

Conclusion: In this prospective multi-site study from July 2020, a substantial proportion of ED patients required SARS-CoV-2 testing, isolation and enhanced infection prevention and control precautions. Presence of SARS-CoV-2 on nasopharyngeal swab was not associated with death or mechanical ventilation.
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http://dx.doi.org/10.1111/1742-6723.13651DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7536936PMC
February 2021

MTSS1/Src family kinase dysregulation underlies multiple inherited ataxias.

Proc Natl Acad Sci U S A 2018 12 7;115(52):E12407-E12416. Epub 2018 Dec 7.

Program in Epithelial Biology, Stanford University School of Medicine, Stanford, CA 94305;

The genetically heterogeneous spinocerebellar ataxias (SCAs) are caused by Purkinje neuron dysfunction and degeneration, but their underlying pathological mechanisms remain elusive. The Src family of nonreceptor tyrosine kinases (SFK) are essential for nervous system homeostasis and are increasingly implicated in degenerative disease. Here we reveal that the SFK suppressor Missing-in-metastasis (MTSS1) is an ataxia locus that links multiple SCAs. MTSS1 loss results in increased SFK activity, reduced Purkinje neuron arborization, and low basal firing rates, followed by cell death. Surprisingly, mouse models for SCA1, SCA2, and SCA5 show elevated SFK activity, with SCA1 and SCA2 displaying dramatically reduced MTSS1 protein levels through reduced gene expression and protein translation, respectively. Treatment of each SCA model with a clinically approved Src inhibitor corrects Purkinje neuron basal firing and delays ataxia progression in MTSS1 mutants. Our results identify a common SCA therapeutic target and demonstrate a key role for MTSS1/SFK in Purkinje neuron survival and ataxia progression.
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http://dx.doi.org/10.1073/pnas.1816177115DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6310854PMC
December 2018

Loss of cerebellar glutamate transporters EAAT4 and GLAST differentially affects the spontaneous firing pattern and survival of Purkinje cells.

Hum Mol Genet 2018 08;27(15):2614-2627

The Centre for Discovery Brain Sciences, The University of Edinburgh, Hugh Robson Building, Edinburgh, UK.

Loss of excitatory amino acid transporters (EAATs) has been implicated in a number of human diseases including spinocerebellar ataxias, Alzhiemer's disease and motor neuron disease. EAAT4 and GLAST/EAAT1 are the two predominant EAATs responsible for maintaining low extracellular glutamate levels and preventing neurotoxicity in the cerebellum, the brain region essential for motor control. Here using genetically modified mice we identify new critical roles for EAAT4 and GLAST/EAAT1 as modulators of Purkinje cell (PC) spontaneous firing patterns. We show high EAAT4 levels, by limiting mGluR1 signalling, are essential in constraining inherently heterogeneous firing of zebrin-positive PCs. Moreover mGluR1 antagonists were found to restore regular spontaneous PC activity and motor behaviour in EAAT4 knockout mice. In contrast, GLAST/EAAT1 expression is required to sustain normal spontaneous simple spike activity in low EAAT4 expressing (zebrin-negative) PCs by restricting NMDA receptor activation. Blockade of NMDA receptor activity restores spontaneous activity in zebrin-negative PCs of GLAST knockout mice and furthermore alleviates motor deficits. In addition both transporters have differential effects on PC survival, with zebrin-negative PCs more vulnerable to loss of GLAST/EAAT1 and zebrin-positive PCs more vulnerable to loss of EAAT4. These findings reveal that glutamate transporter dysfunction through elevated extracellular glutamate and the aberrant activation of extrasynaptic receptors can disrupt cerebellar output by altering spontaneous PC firing. This expands our understanding of disease mechanisms in cerebellar ataxias and establishes EAATs as targets for restoring homeostasis in a variety of neurological diseases where altered cerebellar output is now thought to play a key role in pathogenesis.
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http://dx.doi.org/10.1093/hmg/ddy169DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6049029PMC
August 2018

C9ORF72 repeat expansion causes vulnerability of motor neurons to Ca-permeable AMPA receptor-mediated excitotoxicity.

Nat Commun 2018 01 24;9(1):347. Epub 2018 Jan 24.

MRC Centre for Regenerative Medicine, University of Edinburgh, Edinburgh, EH16 4UU, UK.

Mutations in C9ORF72 are the most common cause of familial amyotrophic lateral sclerosis (ALS). Here, through a combination of RNA-Seq and electrophysiological studies on induced pluripotent stem cell (iPSC)-derived motor neurons (MNs), we show that increased expression of GluA1 AMPA receptor (AMPAR) subunit occurs in MNs with C9ORF72 mutations that leads to increased Ca-permeable AMPAR expression and results in enhanced selective MN vulnerability to excitotoxicity. These deficits are not found in iPSC-derived cortical neurons and are abolished by CRISPR/Cas9-mediated correction of the C9ORF72 repeat expansion in MNs. We also demonstrate that MN-specific dysregulation of AMPAR expression is also present in C9ORF72 patient post-mortem material. We therefore present multiple lines of evidence for the specific upregulation of GluA1 subunits in human mutant C9ORF72 MNs that could lead to a potential pathogenic excitotoxic mechanism in ALS.
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http://dx.doi.org/10.1038/s41467-017-02729-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5783946PMC
January 2018

PLAA Mutations Cause a Lethal Infantile Epileptic Encephalopathy by Disrupting Ubiquitin-Mediated Endolysosomal Degradation of Synaptic Proteins.

Am J Hum Genet 2017 May 13;100(5):706-724. Epub 2017 Apr 13.

MRC Human Genetics Unit, Institute of Genetics and Molecular Medicine, University of Edinburgh, Edinburgh EH4 2XU, UK. Electronic address:

During neurotransmission, synaptic vesicles undergo multiple rounds of exo-endocytosis, involving recycling and/or degradation of synaptic proteins. While ubiquitin signaling at synapses is essential for neural function, it has been assumed that synaptic proteostasis requires the ubiquitin-proteasome system (UPS). We demonstrate here that turnover of synaptic membrane proteins via the endolysosomal pathway is essential for synaptic function. In both human and mouse, hypomorphic mutations in the ubiquitin adaptor protein PLAA cause an infantile-lethal neurodysfunction syndrome with seizures. Resulting from perturbed endolysosomal degradation, Plaa mutant neurons accumulate K63-polyubiquitylated proteins and synaptic membrane proteins, disrupting synaptic vesicle recycling and neurotransmission. Through characterization of this neurological intracellular trafficking disorder, we establish the importance of ubiquitin-mediated endolysosomal trafficking at the synapse.
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http://dx.doi.org/10.1016/j.ajhg.2017.03.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5420347PMC
May 2017

Posterior cerebellar Purkinje cells in an SCA5/SPARCA1 mouse model are especially vulnerable to the synergistic effect of loss of β-III spectrin and GLAST.

Hum Mol Genet 2016 10;25(20):4448-4461

The Centre for Integrative Physiology, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, UK.

Clinical phenotypes of spinocerebellar ataxia type-5 (SCA5) and spectrin-associated autosomal recessive cerebellar ataxia type-1 (SPARCA1) are mirrored in mice lacking β-III spectrin (β-III-/-). One function of β-III spectrin is the stabilization of the Purkinje cell-specific glutamate transporter EAAT4 at the plasma membrane. In β-III-/- mice EAAT4 levels are reduced from an early age. In contrast levels of the predominant cerebellar glutamate transporter GLAST, expressed in Bergmann glia, only fall progressively from 3 months onwards. Here we elucidated the roles of these two glutamate transporters in cerebellar pathogenesis mediated through loss of β-III spectrin function by studying EAAT4 and GLAST knockout mice as well as crosses of both with β-III-/- mice. Our data demonstrate that EAAT4 loss, but not abnormal AMPA receptor composition, in young β-III-/- mice underlies early Purkinje cell hyper-excitability and that subsequent loss of GLAST, superimposed on the earlier deficiency of EAAT4, is responsible for Purkinje cell loss and progression of motor deficits. Yet the loss of GLAST appears to be independent of EAAT4 loss, highlighting that other aspects of Purkinje cell dysfunction underpin the pathogenic loss of GLAST. Finally, our results demonstrate that Purkinje cells in the posterior cerebellum of β-III-/- mice are most susceptible to the combined loss of EAAT4 and GLAST, with degeneration of proximal dendrites, the site of climbing fibre innervation, most pronounced. This highlights the necessity for efficient glutamate clearance from these regions and identifies dysregulation of glutamatergic neurotransmission particularly within the posterior cerebellum as a key mechanism in SCA5 and SPARCA1 pathogenesis.
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http://dx.doi.org/10.1093/hmg/ddw274DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5409221PMC
October 2016

Cerebellar ataxias: β-III spectrin's interactions suggest common pathogenic pathways.

J Physiol 2016 08 24;594(16):4661-76. Epub 2016 Apr 24.

Centre for Integrative Physiology, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh, EH8 9XD, UK.

Spinocerebellar ataxias (SCAs) are a genetically heterogeneous group of disorders all characterised by postural abnormalities, motor deficits and cerebellar degeneration. Animal and in vitro models have revealed β-III spectrin, a cytoskeletal protein present throughout the soma and dendritic tree of cerebellar Purkinje cells, to be required for the maintenance of dendritic architecture and for the trafficking and/or stabilisation of several membrane proteins: ankyrin-R, cell adhesion molecules, metabotropic glutamate receptor-1 (mGluR1), voltage-gated sodium channels (Nav ) and glutamate transporters. This scaffold of interactions connects β-III spectrin to a wide variety of proteins implicated in the pathology of many SCAs. Heterozygous mutations in the gene encoding β-III spectrin (SPTBN2) underlie SCA type-5 whereas homozygous mutations cause spectrin associated autosomal recessive ataxia type-1 (SPARCA1), an infantile form of ataxia with cognitive impairment. Loss-of β-III spectrin function appears to underpin cerebellar dysfunction and degeneration in both diseases resulting in thinner dendrites, excessive dendritic protrusion with loss of planarity, reduced resurgent sodium currents and abnormal glutamatergic neurotransmission. The initial physiological consequences are a decrease in spontaneous activity and excessive excitation, likely to be offsetting each other, but eventually hyperexcitability gives rise to dark cell degeneration and reduced cerebellar output. Similar molecular mechanisms have been implicated for SCA1, 2, 3, 7, 13, 14, 19, 22, 27 and 28, highlighting alterations to intrinsic Purkinje cell activity, dendritic architecture and glutamatergic transmission as possible common mechanisms downstream of various loss-of-function primary genetic defects. A key question for future research is whether similar mechanisms underlie progressive cerebellar decline in normal ageing.
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http://dx.doi.org/10.1113/JP271195DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4983618PMC
August 2016

"Perhaps Irrelevant". The Iconography of Tycho Brahe's Small Gilt Brass Quadrant.

Nuncius 2015 ;30(1):9-36

When Tycho Brahe published a description of his astronomical instruments in 1598 as part of a strategy to procure royal patronage, it was not with one of his grander, precision measurement tools that he opened his account, but rather a small brass quadrant with limited observational utility. The defining feature of this instrument was seemingly a small emblematic image inscribed within the arc of the quadrant. Through this symbolic motif Tycho conveyed a moralising message about the relative worth of astronomy. Considering a range of visual productions that may have influenced his iconography, the present paper situates the quadrant within the broader context of Renaissance visual culture and examines the significance of the quadrant in Tycho's wider instrument collection.
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November 2015

De novo point mutations in patients diagnosed with ataxic cerebral palsy.

Brain 2015 Jul 16;138(Pt 7):1817-32. Epub 2015 May 16.

4 Nuffield Department of Clinical Neurosciences, University of Oxford, Oxford OX3 9DU, UK 16 Department of Clinical Genetics, Churchill Hospital, Oxford University Hospitals NHS Trust, Oxford, OX3 7LJ, UK

Cerebral palsy is a sporadic disorder with multiple likely aetiologies, but frequently considered to be caused by birth asphyxia. Genetic investigations are rarely performed in patients with cerebral palsy and there is little proven evidence of genetic causes. As part of a large project investigating children with ataxia, we identified four patients in our cohort with a diagnosis of ataxic cerebral palsy. They were investigated using either targeted next generation sequencing or trio-based exome sequencing and were found to have mutations in three different genes, KCNC3, ITPR1 and SPTBN2. All the mutations were de novo and associated with increased paternal age. The mutations were shown to be pathogenic using a combination of bioinformatics analysis and in vitro model systems. This work is the first to report that the ataxic subtype of cerebral palsy can be caused by de novo dominant point mutations, which explains the sporadic nature of these cases. We conclude that at least some subtypes of cerebral palsy may be caused by de novo genetic mutations and patients with a clinical diagnosis of cerebral palsy should be genetically investigated before causation is ascribed to perinatal asphyxia or other aetiologies.
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http://dx.doi.org/10.1093/brain/awv117DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4572487PMC
July 2015

β-III spectrin underpins ankyrin R function in Purkinje cell dendritic trees: protein complex critical for sodium channel activity is impaired by SCA5-associated mutations.

Hum Mol Genet 2014 Jul 6;23(14):3875-82. Epub 2014 Mar 6.

The Centre for Integrative Physiology and Euan MacDonald Centre for Motor Neuron Disease Research, The University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, UK and

Beta III spectrin is present throughout the elaborate dendritic tree of cerebellar Purkinje cells and is required for normal neuronal morphology and cell survival. Spinocerebellar ataxia type 5 (SCA5) and spectrin associated autosomal recessive cerebellar ataxia type 1 are human neurodegenerative diseases involving progressive gait ataxia and cerebellar atrophy. Both disorders appear to result from loss of β-III spectrin function. Further elucidation of β-III spectrin function is therefore needed to understand disease mechanisms and identify potential therapeutic options. Here, we report that β-III spectrin is essential for the recruitment and maintenance of ankyrin R at the plasma membrane of Purkinje cell dendrites. Two SCA5-associated mutations of β-III spectrin both reduce ankyrin R levels at the cell membrane. Moreover, a wild-type β-III spectrin/ankyrin-R complex increases sodium channel levels and activity in cell culture, whereas mutant β-III spectrin complexes fail to enhance sodium currents. This suggests impaired ability to form stable complexes between the adaptor protein ankyrin R and its interacting partners in the Purkinje cell dendritic tree is a key mechanism by which mutant forms of β-III spectrin cause ataxia, initially by Purkinje cell dysfunction and exacerbated by subsequent cell death.
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http://dx.doi.org/10.1093/hmg/ddu103DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4065159PMC
July 2014

Control of synaptic vesicle endocytosis by an extracellular signalling molecule.

Nat Commun 2013 ;4:2394

Centre for Integrative Physiology, George Square, University of Edinburgh, EH8 9XD Scotland, UK.

Signalling cascades control multiple aspects of presynaptic function. Synaptic vesicle endocytosis was assumed to be exempt from modulation, due to its essential role maintaining synaptic vesicle supply and thus neurotransmission. Here we show that brain-derived neurotrophic factor arrests the rephosphorylation of the endocytosis enzyme dynamin I via an inhibition of glycogen synthase kinase 3. This event results in a selective inhibition of activity-dependent bulk endocytosis during high-intensity firing. Furthermore, the continued presence of brain-derived neurotrophic factor alleviates the rundown of neurotransmission during high activity. Thus, synaptic strength can be modulated by extracellular signalling molecules via a direct inhibition of a synaptic vesicle endocytosis mode.
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http://dx.doi.org/10.1038/ncomms3394DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3778765PMC
April 2014

Anaphylaxis treated in a Canadian pediatric hospital: Incidence, clinical characteristics, triggers, and management.

J Allergy Clin Immunol 2013 Sep 27;132(3):739-741.e3. Epub 2013 Jul 27.

Division of Clinical Epidemiology, Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada; Division of Allergy and Clinical Immunology, Department of Medicine, McGill University Health Center, Montreal, Quebec, Canada.

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http://dx.doi.org/10.1016/j.jaci.2013.06.016DOI Listing
September 2013

Recessive mutations in SPTBN2 implicate β-III spectrin in both cognitive and motor development.

PLoS Genet 2012 6;8(12):e1003074. Epub 2012 Dec 6.

Wellcome Trust Centre for Human Genetics, University of Oxford, Oxford, United Kingdom.

β-III spectrin is present in the brain and is known to be important in the function of the cerebellum. Heterozygous mutations in SPTBN2, the gene encoding β-III spectrin, cause Spinocerebellar Ataxia Type 5 (SCA5), an adult-onset, slowly progressive, autosomal-dominant pure cerebellar ataxia. SCA5 is sometimes known as "Lincoln ataxia," because the largest known family is descended from relatives of the United States President Abraham Lincoln. Using targeted capture and next-generation sequencing, we identified a homozygous stop codon in SPTBN2 in a consanguineous family in which childhood developmental ataxia co-segregates with cognitive impairment. The cognitive impairment could result from mutations in a second gene, but further analysis using whole-genome sequencing combined with SNP array analysis did not reveal any evidence of other mutations. We also examined a mouse knockout of β-III spectrin in which ataxia and progressive degeneration of cerebellar Purkinje cells has been previously reported and found morphological abnormalities in neurons from prefrontal cortex and deficits in object recognition tasks, consistent with the human cognitive phenotype. These data provide the first evidence that β-III spectrin plays an important role in cortical brain development and cognition, in addition to its function in the cerebellum; and we conclude that cognitive impairment is an integral part of this novel recessive ataxic syndrome, Spectrin-associated Autosomal Recessive Cerebellar Ataxia type 1 (SPARCA1). In addition, the identification of SPARCA1 and normal heterozygous carriers of the stop codon in SPTBN2 provides insights into the mechanism of molecular dominance in SCA5 and demonstrates that the cell-specific repertoire of spectrin subunits underlies a novel group of disorders, the neuronal spectrinopathies, which includes SCA5, SPARCA1, and a form of West syndrome.
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http://dx.doi.org/10.1371/journal.pgen.1003074DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3516553PMC
May 2013

β-III spectrin is critical for development of purkinje cell dendritic tree and spine morphogenesis.

J Neurosci 2011 Nov;31(46):16581-90

Department of Neurology and Neuroscience, Johns Hopkins University, Baltimore, Maryland 21205, USA.

Mutations in the gene encoding β-III spectrin give rise to spinocerebellar ataxia type 5, a neurodegenerative disease characterized by progressive thinning of the molecular layer, loss of Purkinje cells and increasing motor deficits. A mouse lacking full-length β-III spectrin (β-III⁻/⁻) displays a similar phenotype. In vitro and in vivo analyses of Purkinje cells lacking β-III spectrin, reveal a critical role for β-III spectrin in Purkinje cell morphological development. Disruption of the normally well ordered dendritic arborization occurs in Purkinje cells from β-III⁻/⁻ mice, specifically showing a loss of monoplanar organization, smaller average dendritic diameter and reduced densities of Purkinje cell spines and synapses. Early morphological defects appear to affect distribution of dendritic, but not axonal, proteins. This study confirms that thinning of the molecular layer associated with disease pathogenesis is a consequence of Purkinje cell dendritic degeneration, as Purkinje cells from 8-month-old β-III⁻/⁻ mice have drastically reduced dendritic volumes, surface areas and total dendritic lengths compared with 5- to 6-week-old β-III⁻/⁻ mice. These findings highlight a critical role of β-III spectrin in dendritic biology and are consistent with an early developmental defect in β-III⁻/⁻ mice, with abnormal Purkinje cell dendritic morphology potentially underlying disease pathogenesis.
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http://dx.doi.org/10.1523/JNEUROSCI.3332-11.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3374928PMC
November 2011

Beta-III spectrin mutation L253P associated with spinocerebellar ataxia type 5 interferes with binding to Arp1 and protein trafficking from the Golgi.

Hum Mol Genet 2010 Sep 5;19(18):3634-41. Epub 2010 Jul 5.

The Centre for Integrative Physiology, The University of Edinburgh, Edinburgh, UK.

Spinocerebellar ataxia type 5 (SCA5) is an autosomal dominant neurodegenerative disorder caused by mutations in beta-III spectrin. A mouse lacking full-length beta-III spectrin has a phenotype closely mirroring symptoms of SCA5 patients. Here we report the analysis of heterozygous animals, which show no signs of ataxia or cerebellar degeneration up to 2 years of age. This argues against haploinsufficiency as a disease mechanism and points towards human mutations having a dominant-negative effect on wild-type (WT) beta-III spectrin function. Cell culture studies using beta-III spectrin with a mutation associated with SCA5 (L253P) reveal that mutant protein, instead of being found at the cell membrane, appears trapped in the cytoplasm associated with the Golgi apparatus. Furthermore, L253P beta-III spectrin prevents correct localization of WT beta-III spectrin and prevents EAAT4, a protein known to interact with beta-III spectrin, from reaching the plasma membrane. Interaction of beta-III spectrin with Arp1, a subunit of the dynactin-dynein complex, is also lost with the L253P substitution. Despite intracellular accumulation of proteins, this cellular stress does not induce the unfolded protein response, implying the importance of membrane protein loss in disease pathogenesis. Incubation at lower temperature (25 degrees C) rescues L253P beta-III spectrin interaction with Arp1 and normal protein trafficking to the membrane. These data provide evidence for a dominant-negative effect of an SCA5 mutation and show for the first time that trafficking of both beta-III spectrin and EAAT4 from the Golgi is disrupted through failure of the L253P mutation to interact with Arp1.
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http://dx.doi.org/10.1093/hmg/ddq279DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2928133PMC
September 2010

Loss of beta-III spectrin leads to Purkinje cell dysfunction recapitulating the behavior and neuropathology of spinocerebellar ataxia type 5 in humans.

J Neurosci 2010 Apr;30(14):4857-67

The Centre for Integrative Physiology, The University of Edinburgh, George Square, Edinburgh EH8 9XD, United Kingdom.

Mutations in SPTBN2, the gene encoding beta-III spectrin, cause spinocerebellar ataxia type 5 in humans (SCA5), a neurodegenerative disorder resulting in loss of motor coordination. How these mutations give rise to progressive ataxia and what the precise role beta-III spectrin plays in normal cerebellar physiology are unknown. We developed a mouse lacking full-length beta-III spectrin and found that homozygous mice reproduced features of SCA5 including gait abnormalities, tremor, deteriorating motor coordination, Purkinje cell loss, and cerebellar atrophy (molecular layer thinning). In vivo analysis reveals an age-related reduction in simple spike firing rate in surviving beta-III(-/-) Purkinje cells, whereas in vitro studies show these neurons to have reduced spontaneous firing, smaller sodium currents, and dysregulation of glutamatergic neurotransmission. Our data suggest an early loss of EAAT4- (protein interactor of beta-III spectrin) and a subsequent loss of GLAST-mediated uptake may play a role in neuronal pathology. These findings implicate a loss of beta-III spectrin function in SCA5 pathogenesis and indicate that there are at least two physiological effects of beta-III spectrin loss that underpin a progressive loss of inhibitory cerebellar output, namely an intrinsic Purkinje cell membrane defect due to reduced sodium currents and alterations in glutamate signaling.
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http://dx.doi.org/10.1523/JNEUROSCI.6065-09.2010DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2857506PMC
April 2010

A TASK-like pH- and amine-sensitive 'leak' K+ conductance regulates neonatal rat facial motoneuron excitability in vitro.

Eur J Neurosci 2005 Feb;21(3):679-91

Division of Neuroscience, University of Edinburgh, 1 George Square, Edinburgh EH8 9JZ, UK.

A 'leak' potassium (K+) conductance (gK(Leak)) modulated by amine neurotransmitters is a major determinant of neonatal rat facial motoneuron excitability. Although the molecular identity of gK(Leak) is unknown, TASK-1 and TASK-3 channel mRNA is found in facial motoneurons. External pH, across the physiological range (pH 6-8), and noradrenaline (NA) modulated a conductance that displayed a relatively linear current/voltage relationship and reversed at the K+ equilibrium potential, consistent with inhibition of gK(Leak). The pH-sensitive current (I(pH)), was maximal around pH 8, fully inhibited near pH 6 and was described by a modified Hill equation with a pK of 7.1. The NA-induced current (I(NA)) was occluded at pH 6 and enhanced at pH 7.7. The TASK-1 selective inhibitor anandamide (10 microM), its stable analogue methanandamide (10 microM), the TASK-3 selective inhibitor ruthenium red (10 microM) and Zn2+ (100-300 microM) all failed to alter facial motoneuron membrane current or block I(NA) or I(pH). Isoflurane, a volatile anaesthetic that enhances heteromeric TASK-1/TASK-3 currents, increased gK(Leak). Ba2+, Cs+ and Rb+ blocked I(NA) and I(pH) voltage-dependently with maximal block at hyperpolarized potentials. 4-Aminopyridine (4-AP, 4 mM) voltage-independently blocked I(NA) and I(pH). In summary, gK(Leak) displays some of the properties of a TASK-like conductance. The linearity of gK(Leak) and an independence of activation on external [K+] suggests against pH-sensitive inwardly rectifying K+ channels. Our results argue against principal contributions to gK(Leak) by homomeric TASK-1 or TASK-3 channels, while the potentiation by isoflurane supports a predominant role for heterodimeric TASK-1/TASK-3 channels.
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http://dx.doi.org/10.1111/j.1460-9568.2005.03898.xDOI Listing
February 2005