Cloning, developmental regulation and neural localization of rat ɛ-sarcoglycan

Genetics and Pathogenesis of Dystonia

Dystonia is a clinically and genetically highly heterogeneous neurological disorder characterized by abnormal movements and postures caused by involuntary sustained or intermittent muscle contractions. A number of groundbreaking genetic and molecular insights have recently been gained. While they enable genetic testing and counseling, their translation into new therapies is still limited. However, we are beginning to understand shared pathophysiological pathways and molecular mechanisms. It has become clear that dystonia results from a dysfunctional network involving the basal ganglia, cerebellum, thalamus, and cortex. On the molecular level, more than a handful of, often intertwined, pathways have been linked to pathogenic variants in dystonia genes, including gene transcription during neurodevelopment (e.g., KMT2B, THAP1), calcium homeostasis (e.g., ANO3, HPCA), striatal dopamine signaling (e.g., GNAL), endoplasmic reticulum stress response (e.g., EIF2AK2, PRKRA, TOR1A), autophagy (e.g., VPS16), and others. Thus, different forms of dystonia can be molecularly grouped, which may facilitate treatment development in the future.

ε-Sarcoglycan: Unraveling the Myoclonus-Dystonia Gene

Myoclonus-dystonia (MD) is a rare childhood-onset movement disorder, with an estimated prevalence of about 2 per 1,000,.000 in Europe, characterized by myoclonic jerks in combination with focal or segmental dystonia. Pathogenic variants in the gene encoding ε-sarcoglycan (SGCE), a maternally imprinted gene, are the most frequent genetic cause of MD. To date, the exact role of ε-sarcoglycan and the pathogenic mechanisms that lead to MD are still unknown. However, there are more than 40 reported isoforms of human ε-sarcoglycan, pointing to a complex biology of this protein. Additionally, some of these are brain-specific isoforms, which may suggest an important role within the central nervous system. In the present review, we aim to provide an overview of the current state of knowledge of ε-sarcoglycan. We will focus on the genetic landscape of SGCE and the presence and plausible role of ε-sarcoglycan in the brain. Finally, we discuss the importance of the brain-specific isoforms and hypothesize that SGCE may play essential roles in normal synaptic functioning and their alteration will be strongly related to MD.

Proenkephalin Decreases in Cerebrospinal Fluid with Symptom Progression of Huntington's Disease

OBJECTIVE

Identifying molecular changes that contribute to the onset and progression of Huntington's disease (HD) is of importance for the development and evaluation of potential therapies.

METHODS

We conducted an unbiased mass-spectrometry proteomic analysis on the cerebrospinal fluid of 12 manifest HD patients (ManHD), 13 pre-manifest (preHD), and 38 controls. A biologically plausible and significant possible biomarker was validated in samples from a separate cohort of patients and controls consisting of 23 ManHD patients and 23 controls.

RESULTS

In ManHD compared to preHD, 10 proteins were downregulated and 43 upregulated. Decreased levels of proenkephalin (PENK) and transthyretin were closely linked to HD symptom severity, whereas levels of 15 upregulated proteins were associated with symptom severity. The decreased PENK levels were replicated in the separate cohort where absolute quantitation was performed.

CONCLUSIONS

We hypothesize that declining PENK levels reflect the degeneration of medium spiny neurons (MSNs) that produce PENK and that assays for PENK may serve as a surrogate marker for the state of MSNs in HD. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Presynaptic PRRT2 Deficiency Causes Cerebellar Dysfunction and Paroxysmal Kinesigenic Dyskinesia

PRRT2 loss-of-function mutations have been associated with familial paroxysmal kinesigenic dyskinesia (PKD), infantile convulsions and choreoathetosis, and benign familial infantile seizures. Dystonia is the foremost involuntary movement disorder manifest by patients with PKD. Using a lacZ reporter and quantitative reverse-transcriptase PCR, we mapped the temporal and spatial distribution of Prrt2 in mouse brain and showed the highest levels of expression in cerebellar cortex. Further investigation into PRRT2 localization within the cerebellar cortex revealed that Prrt2 transcripts reside in granule cells but not Purkinje cells or interneurons within cerebellar cortex, and PRRT2 is presynaptically localized in the molecular layer. Analysis of synapses in the cerebellar molecular layer via electron microscopy showed that Prrt2^-/- mice have increased numbers of docked vesicles but decreased vesicle numbers overall. In addition to impaired performance on several motor tasks, approximately 5% of Prrt2^-/- mice exhibited overt PKD with clear face validity manifest as dystonia. In Prrt2 mutants, we found reduced parallel fiber facilitation at parallel fiber-Purkinje cell synapses, reduced Purkinje cell excitability, and normal cerebellar nuclear excitability, establishing a potential mechanism by which altered cerebellar activity promotes disinhibition of the cerebellar nuclei, driving motor abnormalities in PKD. Overall, our findings replicate, refine, and expand upon previous work with PRRT2 mouse models, contribute to understanding of paroxysmal disorders of the nervous system, and provide mechanistic insight into the role of cerebellar cortical dysfunction in dystonia.

Twenty years on: Myoclonus-dystonia and ε-sarcoglycan - neurodevelopment, channel, and signaling dysfunction

Myoclonus-dystonia is a clinical syndrome characterized by a typical childhood onset of myoclonic jerks and dystonia involving the neck, trunk, and upper limbs. Psychiatric symptomatology, namely, alcohol dependence and phobic and obsessive-compulsive disorder, is also part of the clinical picture. Zonisamide has demonstrated effectiveness at reducing both myoclonus and dystonia, and deep brain stimulation seems to be an effective and long-lasting therapeutic option for medication-refractory cases. In a subset of patients, myoclonus-dystonia is associated with pathogenic variants in the epsilon-sarcoglycan gene, located on chromosome 7q21, and up to now, more than 100 different pathogenic variants of the epsilon-sarcoglycan gene have been described. In a few families with a clinical phenotype resembling myoclonus-dystonia associated with distinct clinical features, variants have been identified in genes involved in novel pathways such as calcium channel regulation and neurodevelopment. Because of phenotypic similarities with epsilon-sarcoglycan gene-related myoclonus-dystonia, these conditions can be collectively classified as "myoclonus-dystonia syndromes." In the present article, we present myoclonus-dystonia caused by epsilon-sarcoglycan gene mutations, with a focus on genetics and underlying disease mechanisms. Second, we review those conditions falling within the spectrum of myoclonus-dystonia syndromes, highlighting their genetic background and involved pathways. Finally, we critically discuss the normal and pathological function of the epsilon-sarcoglycan gene and its product, suggesting a role in the stabilization of the dopaminergic membrane via regulation of calcium homeostasis and in the neurodevelopmental process involving the cerebello-thalamo-pallido-cortical network. © 2019 International Parkinson and Movement Disorder Society.

Delineating cerebellar mechanisms in DYT11 myoclonus-dystonia

BACKGROUND

Recent research has highlighted the role of the cerebellum in the pathophysiology of myoclonus-dystonia syndrome as a result of mutations in the ɛ-sarcoglycan gene (DYT11). Specifically, a cerebellar-dependent saccadic adaptation task is dramatically impaired in this patient group.

OBJECTIVES

The objective of this study was to investigate whether saccadic deficits coexist with impairments of limb adaptation to provide a potential mechanism linking cerebellar dysfunction to the movement disorder within symptomatic body regions.

METHODS

Limb adaptation to visuomotor (visual feedback rotated by 30°) and forcefield (force applied by robot to deviate arm) perturbations were examined in 5 patients with DYT11 and 10 aged-matched controls.

RESULTS

Patients with DYT11 successfully adapted to both types of perturbation. Modelled and averaged summary metrics that captured adaptation behaviors were equivalent to the control group across conditions.

CONCLUSIONS

DYT11 is not characterized by a uniform deficit in adaptation. The previously observed large deficit in saccadic adaption is not reflected in an equivalent deficit in limb adaptation in symptomatic body regions. We suggest potential mechanisms at the root of this discordance and identify key research questions that need future study. © 2018 International Parkinson and Movement Disorder Society.

Role of major and brain-specific Sgce isoforms in the pathogenesis of myoclonus-dystonia syndrome

Loss-of-function mutations in SGCE, which encodes ε-sarcoglycan (ε-SG), cause myoclonus-dystonia syndrome (OMIM159900, DYT11). A "major" ε-SG protein derived from CCDS5637.1 (NM_003919.2) and a "brain-specific" protein, that includes sequence derived from alternative exon 11b (CCDS47642.1, NM_001099400.1), are reportedly localized in post- and pre-synaptic membrane fractions, respectively. Moreover, deficiency of the "brain-specific" isoform and other isoforms derived from exon 11b may be central to the pathogenesis of DYT11. However, no animal model supports this hypothesis. Gene-trapped ES cells (CMHD-GT_148G1-3, intron 9 of NM_011360) were used to generate a novel Sgce mouse model (C57BL/6J background) with markedly reduced expression of isoforms derived from exons 3' to exon 9 of NM_011360. Among those brain regions analyzed in adult (2month-old) wild-type (WT) mice, cerebellum showed the highest relative expression of isoforms incorporating exon 11b. Homozygotes (Sgce^{Gt(148G1)Cmhd/Gt(148G1)Cmhd} or Sgce^Gt/Gt) and paternal heterozygotes (Sgce^m+/pGt, m-maternal, p-paternal) showed 60 to 70% reductions in expression of total Sgce. Although expression of the major (NM_011360) and brain-specific (NM_001130189) isoforms was markedly reduced, expression of short isoforms was preserved and relatively small amounts of chimeric ε-SG/β-galactosidase fusion protein was produced by the Sgce gene-trap locus. Immunoaffinity purification followed by mass spectrometry assessments of Sgce^m+/pGt mouse brain using pan- or brain-specific ε-SG antibodies revealed significant reductions of ε-SG and other interacting sarcoglycans. Genome-wide gene-expression data using RNA derived from adult Sgce^m+/pGt mouse cerebellum showed that the top up-regulated genes were involved in cell cycle, cellular development, cell death and survival, while the top down-regulated genes were associated with protein synthesis, cellular development, and cell death and survival. In comparison to WT littermates, Sgce^m+/pGt mice exhibited "tiptoe" gait and stimulus-induced appendicular posturing between Postnatal Days 14 to 16. Abnormalities noted in older Sgce^m+/pGt mice included reduced body weight, altered gait dynamics, and reduced open-field activity. Overt spontaneous or stimulus-sensitive myoclonus was not apparent on the C57BL/6J background or mixed C57BL/6J-BALB/c and C57BL/6J-129S2 backgrounds. Our data confirm that mouse Sgce is a maternally imprinted gene and suggests that short Sgce isoforms may compensate, in part, for deficiency of major and brain-specific Sgce isoforms.

Metabolic changes in DYT11 myoclonus-dystonia

OBJECTIVE

To identify brain regions with metabolic changes in DYT11 myoclonus-dystonia (DYT11-MD) relative to control subjects and to compare metabolic abnormalities in DYT11-MD with those found in other forms of hereditary dystonia and in posthypoxic myoclonus.

METHODS

[(18)F]-fluorodeoxyglucose PET was performed in 6 subjects with DYT11-MD (age 30.5 ± 10.1 years) and in 6 nonmanifesting DYT11 mutation carriers (NM-DYT11; age 59.1 ± 8.9 years) representing the parental generation of the affected individuals. These data were compared to scan data from age-matched healthy control subjects using voxel-based whole brain searches and group differences were considered significant at p < 0.05 (corrected, statistical parametric mapping). As a secondary analysis, overlapping abnormalities were identified by comparisons to hereditary dystonias (DYT1, DYT6, dopa-responsive dystonia) and to posthypoxic myoclonus.

RESULTS

We found significant DYT11 genotype-specific metabolic increases in the inferior pons and in the posterior thalamus as well as reductions in the ventromedial prefrontal cortex. Significant phenotype-related increases were present in the parasagittal cerebellum. This latter abnormality was shared with posthypoxic myoclonus, but not with other forms of dystonia. By contrast, all dystonia cohorts exhibited significant metabolic increases in the superior parietal lobule.

CONCLUSIONS

The findings are consistent with a subcortical myoclonus generator in DYT11-MD, likely involving the cerebellum. By contrast, subtle increases in the superior parietal cortex relate to the additional presence of dystonic symptoms. Although reduced penetrance in DYT11-MD has been attributed to the maternal imprinting epsilon-sarcoglycan mutations, NM-DYT11 carriers showed significant metabolic abnormalities that are not explained by this genetic model.

The genetics of dystonias

Dystonia has been defined as a syndrome of involuntary, sustained muscle contractions affecting one or more sites of the body, frequently causing twisting and repetitive movements or abnormal postures. Dystonia is also a clinical sign that can be the presenting or prominent manifestation of many neurodegenerative and neurometabolic disorders. Etiological categories include primary dystonia, secondary dystonia, heredodegenerative diseases with dystonia, and dystonia plus. Primary dystonia includes syndromes in which dystonia is the sole phenotypic manifestation with the exception that tremor can be present as well. Most primary dystonia begins in adults, and approximately 10% of probands report one or more affected family members. Many cases of childhood- and adolescent-onset dystonia are due to mutations in TOR1A and THAP1. Mutations in THAP1 and CIZ1 have been associated with sporadic and familial adult-onset dystonia. Although significant recent progress had been made in defining the genetic basis for most of the dystonia-plus and heredodegenerative diseases with dystonia, a major gap remains in understanding the genetic etiologies for most cases of adult-onset primary dystonia. Common themes in the cellular biology of dystonia include G1/S cell cycle control, monoaminergic neurotransmission, mitochondrial dysfunction, and the neuronal stress response.

Alteration of striatal dopaminergic neurotransmission in a mouse model of DYT11 myoclonus-dystonia

Background

DYT11 myoclonus-dystonia (M-D) syndrome is a neurological movement disorder characterized by myoclonic jerks and dystonic postures or movement that can be alleviated by alcohol. It is caused by mutations in SGCE encoding ε-sarcoglycan (ε-SG); the mouse homolog of this gene is Sgce. Paternally-inherited Sgce heterozygous knockout (Sgce KO) mice exhibit myoclonus, motor impairment and anxiety- and depression-like behaviors, modeling several clinical symptoms observed in DYT11 M-D patients. The behavioral deficits are accompanied by abnormally high levels of dopamine and its metabolites in the striatum of Sgce KO mice. Neuroimaging studies of DYT11 M-D patients show reduced dopamine D2 receptor (D2R) availability, although the possibility of increased endogenous dopamine, and consequently, competitive D2R occupancy cannot be ruled out.

Methodology/Principal Findings

The protein levels of striatal D2R, dopamine transporter (DAT), and dopamine D1 receptor (D1R) in Sgce KO mice were analyzed by Western blot. The striatal dopamine release after amphetamine injection in Sgce KO mice were analyzed by microdialysis in vivo. The striatal D2R was significantly decreased in Sgce KO mice without altering DAT and D1R. Sgce KO mice also exhibited a significant increase of dopamine release after amphetamine injection in comparison to wild-type (WT) littermates.

Conclusion/Significance

The results suggest ε-SG may have a role in the regulation of D2R expression. The loss of ε-SG results in decreased striatal D2R, and subsequently leads to increased discharge of dopamine which could contribute to the behavioral impairment observed in DYT11 dystonia patients and in Sgce KO mice. The results suggest that reduction of striatal D2R and enhanced striatal dopamine release may contribute to the pathophysiology of DYT11 M-D patients.

Abnormal nuclear envelope in the cerebellar Purkinje cells and impaired motor learning in DYT11 myoclonus-dystonia mouse models

Myoclonus-dystonia (M-D) is a movement disorder characterized by myoclonic jerks with dystonia. DYT11 M-D is caused by mutations in SGCE which codes for ɛ-sarcoglycan. SGCE is maternally imprinted and paternally expressed. Abnormal nuclear envelope has been reported in mouse models of DYT1 generalized torsion dystonia. However, it is not known whether similar alterations occur in DYT11 M-D. We developed a mouse model of DYT11 M-D using paternally inherited Sgce heterozygous knockout (Sgce KO) mice and reported that they had myoclonus and motor coordination and learning deficits in the beam-walking test. However, the specific brain regions that contribute to these phenotypes have not been identified. Since ɛ-sarcoglycan is highly expressed in the cerebellar Purkinje cells, here we examined the nuclear envelope in these cells using a transmission electron microscope and found that they are abnormal in Sgce KO mice. Our results put DYT11 M-D in a growing family of nuclear envelopathies. To analyze the effect of loss of ɛ-sarcoglycan function in the cerebellar Purkinje cells, we produced paternally inherited cerebellar Purkinje cell-specific Sgce conditional knockout (Sgce pKO) mice. Sgce pKO mice showed motor learning deficits, while they did not show abnormal nuclear envelope in the cerebellar Purkinje cells, robust motor deficits, or myoclonus. The results suggest that ɛ-sarcoglycan in the cerebellar Purkinje cells contributes to the motor learning, while loss of ɛ-sarcoglycan in other brain regions may contribute to nuclear envelope abnormality, myoclonus and motor coordination deficits.

Abnormal nuclear envelopes in the striatum and motor deficits in DYT11 myoclonus-dystonia mouse models

DYT11 myoclonus-dystonia (M-D) is a movement disorder characterized by myoclonic jerks with dystonic symptoms and caused by mutations in paternally expressed SGCE, which codes for ε-sarcoglycan. Paternally inherited Sgce heterozygous knock-out (KO) mice exhibit motor deficits and spontaneous myoclonus. Abnormal nuclear envelopes have been reported in cellular and mouse models of early-onset DYT1 generalized torsion dystonia; however, the relationship between the abnormal nuclear envelopes and motor symptoms are not clear. Furthermore, it is not known whether abnormal nuclear envelope exists in non-DYT1 dystonia. In the present study, abnormal nuclear envelopes in the striatal medium spiny neurons (MSNs) were found in Sgce KO mice. To analyze whether the loss of ε-sarcoglycan in the striatum alone causes abnormal nuclear envelopes, motor deficits or myoclonus, we produced paternally inherited striatum-specific Sgce conditional KO (Sgce sKO) mice and analyzed their phenotypes. Sgce sKO mice exhibited motor deficits in both beam-walking and accelerated rotarod tests, while they did not exhibit abnormal nuclear envelopes, alteration in locomotion, or myoclonus. The results suggest that the loss of ε-sarcoglycan in the striatum contributes to motor deficits, while it alone does not produce abnormal nuclear envelopes or myoclonus. Development of therapies targeting the striatum to compensate for the loss of ε-sarcoglycan function may rescue the motor deficits in DYT11 M-D patients.

Milestones in dystonia

The last 25 years have seen remarkable advances in our understanding of the genetic etiologies of dystonia, new approaches into dissecting underlying pathophysiology, and independent progress in identifying effective treatments. In this review we highlight some of these advances, especially the genetic findings that have taken us from phenomenological to molecular-based diagnoses. Twenty DYT loci have been designated and 10 genes identified, all based on linkage analyses in families. Hand in hand with these genetic findings, neurophysiological and imaging techniques have been employed that have helped illuminate the similarities and differences among the various etiological dystonia subtypes. This knowledge is just beginning to yield new approaches to treatment including those based on DYT1 animal models. Despite the lag in identifying genetically based therapies, effective treatments, including impressive benefits from deep brain stimulation and botulinum toxin chemodenervation, have marked the last 25 years. The challenge ahead includes continued advancement into understanding dystonia's many underlying causes and associated pathology and using this knowledge to advance treatment including preventing genetic disease expression.

Myoclonus-dystonia syndrome

Myoclonus dystonia syndrome (MDS) refers to a group of heterogeneous nondegenerative clinical conditions characterized by the association of myoclonus and dystonia as the only or prominent symptom. The "core" of MDS is represented by inherited myoclonus-dystonia (M-D), a disorder with autosomal-dominant inheritance and reduced penetrance, beginning in early childhood with a relatively benign course, with myoclonus as the most predominant and disabling symptom. Alcohol responsiveness and psychiatric symptoms are characteristic features. Mutations in the epsilon-sarcoglycan gene (SGCE, DYT11) represent the major genetic cause, but M-D is genetically heterogeneous. In a variable proportion of M-D patients no mutation is found, and at least one other locus (DYT15) has been linked to the disease. Patients with primary dystonia, with or without the DYT1 mutation, may show irregular and arrhythmic jerky movements associated with dystonia. Usually dystonia is the prominent symptom and the myoclonic jerk involves the same body region; this condition, currently defined as "myoclonic dystonia," is included in the spectrum of MDS. Dopa-responsive dystonia due to mutation in the GTP-CH gene and vitamin E deficiency can present with a phenotype of dystonia and myoclonus in combination; both conditions should be considered in the diagnostic approach to patients since they are potentially treatable.

Earlier onset of motor deficits in mice with double mutations in Dyt1 and Sgce

DYT1 early-onset generalized torsion dystonia is an inherited movement disorder caused by mutations in DYT1 coding for torsinA with ∼30% penetrance. Most of the DYT1 dystonia patients exhibit symptoms during childhood and adolescence. On the other hand, DYT1 mutation carriers without symptoms during these periods mostly do not exhibit symptoms later in their life. Little is known about what controls the timing of the onset, a critical issue for DYT1 mutation carriers. DYT11 myoclonus-dystonia is caused by mutations in SGCE coding for ε-sarcoglycan. Two dystonia patients from a single family with double mutations in DYT1 and SGCE exhibited more severe symptoms. A recent study suggested that torsinA contributes to the quality control of ε-sarcoglycan. Here, we derived mice carrying mutations in both Dyt1 and Sgce and found that these double mutant mice showed earlier onset of motor deficits in beam-walking test. A novel monoclonal antibody against mouse ε-sarcoglycan was developed by using Sgce knock-out mice to avoid the immune tolerance. Western blot analysis suggested that functional deficits of torsinA and ε-sarcoglycan may independently cause motor deficits. Examining additional mutations in other dystonia genes may be beneficial to predict the onset in DYT1 mutation carriers.

[Monogenetic dystonia: revisiting the dopaminergic hypothesis]

Dystonias are clinically and genetically heterogeneous neurological disorders that affect movement, and are the focus of much investigative work. The recent identification of mutations in the gene THAP1 in DYT6 dystonia reopens the very interesting question of the in fine involvement of dopamine in the different types of dystonia. In this review, we will go through the recent literature in order to evaluate the many contributions to this theory as well as to highlight the difficulties in identifying a global regulatory pathway for the different forms of this disease that we are just starting to decipher.

Primary dystonia: molecules and mechanisms

Primary dystonia is characterized by abnormal, involuntary twisting and turning movements that reflect impaired motor system function. The dystonic brain seems normal, in that it contains no overt lesions or evidence of neurodegeneration, but functional brain imaging has uncovered abnormalities involving the cortex, striatum and cerebellum, and diffusion tensor imaging suggests the presence of microstructural defects in white matter tracts of the cerebellothalamocortical circuit. Clinical electrophysiological studies show that the dystonic CNS exhibits aberrant plasticity--perhaps related to deficient inhibitory neurotransmission--in a range of brain structures, as well as the spinal cord. Dystonia is, therefore, best conceptualized as a motor circuit disorder, rather than an abnormality of a particular brain structure. None of the aforementioned abnormalities can be strictly causal, as they are not limited to regions of the CNS subserving clinically affected body parts, and are found in seemingly healthy patients with dystonia-related mutations. The study of dystonia-related genes will, hopefully, help researchers to unravel the chain of events from molecular to cellular to system abnormalities. DYT1 mutations, for example, cause abnormalities within the endoplasmic reticulum-nuclear envelope endomembrane system. Other dystonia-related gene products traffic through the endoplasmic reticulum, suggesting a potential cell biological theme underlying primary dystonia.

No muscle involvement in myoclonus-dystonia caused by epsilon-sarcoglycan gene mutations

Mutations in the epsilon-sarcoglycan gene (SGCE) can cause autosomal dominant inherited myoclonus-dystonia (M-D). Defects in other sarcoglycans; alpha-, beta-, gamma-, and delta can cause autosomal recessive inherited limb girdle muscular dystrophies. epsilon- and alpha-sarcoglycans are very homologous and may substitute for one-another in different tissues. We therefore investigated whether mutations in SGCE also cause abnormalities of skeletal and myocardial muscle. Six patients with clinically and genetically verified M-D and no signs of limb-girdle muscular dystrophy were included. Skeletal muscle biopsies were obtained from all patients, and endomyocardial muscle biopsy from one of the patients. Morphological and immunohistological investigations were performed and compared with controls. Histological and immunohistological investigations of muscle and clinical assessment of muscle strength and mass showed no difference between M-D patients and controls. Our findings indicate that patients with M-D have no signs or symptoms of muscle disease. This suggests a different role of the sarcoglycan complex epsilonbetagammadelta versus alphabetagammadelta complex in humans, as earlier suggested in rodents.

The pathophysiological basis of dystonias

Dystonias comprise a group of movement disorders that are characterized by involuntary movements and postures. Insight into the nature of neuronal dysfunction has been provided by the identification of genes responsible for primary dystonias, the characterization of animal models and functional evaluations and in vivo brain imaging of patients with dystonia. The data suggest that alterations in neuronal development and communication within the brain create a susceptible substratum for dystonia. Although there is no overt neurodegeneration in most forms of dystonia, there are functional and microstructural brain alterations. Dystonia offers a window into the mechanisms whereby subtle changes in neuronal function, particularly in sensorimotor circuits that are associated with motor learning and memory, can corrupt normal coordination and lead to a disabling motor disorder.

SGCE missense mutations that cause myoclonus-dystonia syndrome impair ε-sarcoglycan trafficking to the plasma membrane: modulation by ubiquitination and torsinA

Myoclonus-dystonia syndrome (MDS) is a genetically heterogeneous disorder characterized by myoclonic jerks often seen in combination with dystonia and psychiatric co-morbidities and epilepsy. Mutations in the gene encoding epsilon-sarcoglycan (SGCE) have been found in some patients with MDS. SGCE is a maternally imprinted gene with the disease being inherited in an autosomal dominant pattern with reduced penetrance upon maternal transmission. In the central nervous system, epsilon-sarcoglycan is widely expressed in neurons of the cerebral cortex, basal ganglia, hippocampus, cerebellum and the olfactory bulb. epsilon-Sarcoglycan is located at the plasma membrane in neurons, muscle and transfected cells. To determine the effect of MDS-associated mutations on the function of epsilon-sarcoglycan we examined the biosynthesis and trafficking of wild-type and mutant proteins in cultured cells. In contrast to the wild-type protein, disease-associated epsilon-sarcoglycan missense mutations (H36P, H36R and L172R) produce proteins that are undetectable at the cell surface and are retained intracellularly. These mutant proteins become polyubiquitinated and are rapidly degraded by the proteasome. Furthermore, torsinA, that is mutated in DYT1 dystonia, a rare type of primary dystonia, binds to and promotes the degradation of epsilon-sarcoglycan mutants when both proteins are co-expressed. These data demonstrate that some MDS-associated mutations in SGCE impair trafficking of the mutant protein to the plasma membrane and suggest a role for torsinA and the ubiquitin proteasome system in the recognition and processing of misfolded epsilon-sarcoglycan.

Dp71ab/DAPs complex composition changes during the differentiation process in PC12 cells

PC12 cells express different Dp71 isoforms originated from alternative splicing; one of them, Dp71ab lacks exons 71 and 78. To gain insight into the function of Dp71 isoforms we identified dystrophin associated proteins (DAPs) that associate in vivo with Dp71ab during nerve growth factor (NGF) induced differentiation of PC12 cells. DAPs expression was analyzed by RT-PCR, Western blot and indirect immunofluorescence, showing the presence of each mRNA and protein corresponding to alpha-, beta-, gamma-, delta-, and epsilon-sarcoglycans as well as zeta-sarcoglycan mRNA. Western blot analysis also revealed the expression of beta-dystroglycan, alpha1-syntrophin, alpha1-, and beta-dystrobrevins. We have established that Dp71ab forms a complex with beta-dystroglycan, alpha1-syntrophin, beta-dystrobrevin, and alpha-, beta- and gamma-sarcoglycans in undifferentiated PC12 cells. In differentiated PC12 cells, the complex composition changes since Dp71ab associates only with beta-dystroglycan, alpha1-syntrophin, beta-dystrobrevin, and delta-sarcoglycan. Interestingly, neuronal nitric oxide synthase associates with the Dp71ab/DAPs complex during NGF treatment, raising the possibility that Dp71ab may be involved in signal transduction events during neuronal differentiation.

Movement disorders and alcohol misuse

Many movement disorders, including tics, chorea, tremor, myoclonus and parkinsonism, may result from substance abuse. However, alcohol in particular is associated in a more complex manner with two specific movement disorders, essential tremor (ET) and myoclonus-dystonia (M-D). In this review we discuss the comorbidity of alcohol abuse in both ET and M-D, the ameliorative effects of alcohol in both diseases, and review the data evaluating alcohol abuse secondary to self-medication. We also discuss shared pathophysiologic mechanisms in the understanding of both of these disorders, as the elucidation of the mechanisms by which alcohol exerts its effects may lead to novel therapeutic approaches.

Caytaxin deficiency causes generalized dystonia in rats

The genetically dystonic rat (SD-dt:JFL) is an autosomal recessive model of generalized dystonia. Without cerebellectomy, the dt rat dies prior to Postnatal Day 40. The dt locus was mapped to a 4.2 Mb region on Chr 7q11 and candidate genes were screened with semi-quantitative RT-PCR. Then, Southern blotting and genomic DNA sequencing identified the 3'-long terminal repeat portion of an intracisternal A particle element inserted into Intron 1 of Atcay, the gene which encodes caytaxin. Northern and Western blotting and quantitative real-time RT-PCR defined the Atcay allele in dt rats (Atcay(dt)) as hypomorphic. To establish a framework for functional studies of caytaxin, the developmental expression of rat Atcay transcript was analyzed with Northern blotting, relative quantitative multiplex real-time RT-PCR (QRT-PCR) and in situ hybridization. With a multiple tissue Northern blot, three Atcay transcripts were identified in brain but none were present in heart, spleen, lung, liver, muscle, kidney or testis. With a multiple time-point Northern blot, the same three transcripts were present in cerebellum at Embryonic Day (E15), Postnatal Day 1 (P1), P7, P14, P36 and 8 months. During early development (E15 to P14), the relative proportion of the smallest transcript was increased. QRT-PCR was performed with total RNA from cerebral cortex, striatum, thalamus, hippocampus and cerebellum. Transcript levels peaked at P7 in hippocampus, increased linearly from P1 to P36 in cerebellum, and showed minimal developmental regulation in cerebral cortex. Radioactive in situ hybridization localized Atcay transcript to seemingly all neuronal populations in brain. In cerebellum, Atcay transcript was present in the molecular, Purkinje and granular layers; transcript density in the molecular layer peaked at P14. In the background of previous biochemical, behavioral and electrophysiological studies in the dt rat, our data are compatible with a vital role for caytaxin in the development and neurophysiology of cerebellar cortex.

The sarcoglycan-sarcospan complex localization in mouse retina is independent from dystrophins

The sarcoglycan-sarcospan (SG-SSPN) complex is part of the dystrophin-glycoprotein complex that has been extensively characterized in muscle. To establish the framework for functional studies of sarcoglycans in retina here, we quantified sarcoglycans mRNA levels with real-time reverse transcriptase-polymerase chain reaction (RT-PCR) and performed immunohistochemistry to determine their cellular and subcellular distribution. We showed that the beta-, delta-, gamma-, epsilon-sarcoglycans and sarcospan are expressed in mouse retina. They are localized predominantly in the outer and the inner limiting membranes, probably in the Müller cells and also in the ganglion cells axons where the expression of dystrophins have never been reported. We also investigated the status of the sarcoglycans in the retina of mdx(3cv) mutant mice for all Duchene Muscular Dystrophy (DMD) gene products. The absence of dystrophin did not produce any change in the sarcoglycan-sarcospan components expression and distribution.

Epsilon-sarcoglycan immunoreactivity and mRNA expression in mouse brain

Myoclonus dystonia (M-D) is a hereditary movement disorder caused by a maternally imprinted gene that is often associated with psychiatric symptoms. Most cases of M-D are believed to result from mutations of the epsilon-sarcoglycan protein. The neuroanatomical distribution of epsilon-sarcoglycan-like immunoreactivity in mouse was investigated by using an antiserum against the epsilon-sarcoglycan protein. The expression of epsilon-sarcoglycan mRNA was studied by a sensitive fluorescence in situ hybridization (FISH) method. Immunohistochemistry and FISH revealed a wide distribution of epsilon-sarcoglycan protein and mRNA throughout the mouse brain. High expression levels of epsilon-sarcoglycan mRNA and immunoreactivity were found in the mitral cell layer of the olfactory bulb, the Purkinje cell layer in cerebellum, and the monoaminergic neurons in the mouse midbrain. Immunohistochemistry revealed a similar distribution of epsilon-sarcoglycan protein. Double-labeling FISH showed colocalization of tyrosine hydroxylase and epsilon-sarcoglycan mRNAs within all the midbrain dopaminergic (DAergic) cell groups. By combining FISH with fluorescence immunohistochemistry, coexpression of epsilon-sarcoglycan mRNA and tryptophan hydroxylase immunoreactivity was found in the serotonergic (5-HTergic) neurons within the dorsal raphe nucleus. The distribution of epsilon-sarcoglycan in the mouse brain suggests that the symptom complex of M-D may be related to the effects of decreased epsilon-sarcoglycan activity on the development or function of monoaminergic neurons.

Developmental expression of rat torsinA transcript and protein

A GAG deletion in the gene (TOR1A) for torsinA is associated with childhood-onset generalized dystonia (DYT1). Environmental factors may contribute to development of the phenotype since mutations in TOR1A are clinically penetrant in less than 40% of cases. Median age of onset is 10 and appearance of dystonia after 28 is rare. As a step towards understanding the temporal window of DYT1 disease penetrance, we have examined torsinA transcript and protein expression in rats from the embryonic period through adulthood. With relative quantitative multiplex real-time RT-PCR, we detected torsinA transcript in both neural (cerebellar cortex, striatum, cerebral cortex, thalamus and hippocampus) and non-neural (liver, kidney and heart) tissues at each developmental time point tested (embryonic day 20 [E20], postnatal day 1 [P1], P7, P14, P36, 6 months, 1.5 years). Levels of torsinA transcript were highest at E20 or P1 in all tissues examined except for the cerebellum where transcript levels peaked at P14. Early postnatal levels of torsinA transcript were over three times higher than those seen in adult rats. With quantitative radioactive in situ hybridization, torsinA transcript was widely distributed in brain at all ages with levels peaking at P14 in both cerebellum and striatum. TorsinA-immunoreactivity (IR) was present in neurons throughout the brain. TorsinA-IR was detected in perikarya, dendrites and axons but not nuclei. At P14, prominent expression of torsinA was noted in both striatal cholinergic interneurons and cerebellar Purkinje cells. Our results suggest that torsinA may contribute to postnatal maturational events in the brain such as dendritic arborization and synaptogenesis. Furthermore, the time course of torsinA expression in discrete components of motor networks is compatible with the temporal window of clinical penetrance in DYT1 mutation carriers.