Functional implications of paralog genes in polyglutamine spinocerebellar ataxias

Polyglutamine (polyQ) spinocerebellar ataxias (SCAs) comprise a group of autosomal dominant neurodegenerative disorders caused by (CAG/CAA)n expansions. The elongated stretches of adjacent glutamines alter the conformation of the native proteins inducing neurotoxicity, and subsequent motor and neurological symptoms. Although the etiology and neuropathology of most polyQ SCAs have been extensively studied, only a limited selection of therapies is available. Previous studies on SCA1 demonstrated that ATXN1L, a human duplicated gene of the disease-associated ATXN1, alleviated neuropathology in mice models. Other SCA-associated genes have paralogs (i.e., copies at different chromosomal locations derived from duplication of the parental gene), but their functional relevance and potential role in disease pathogenesis remain unexplored. Here, we review the protein homology, expression pattern, and molecular functions of paralogs in seven polyQ dominant ataxias-SCA1, SCA2, MJD/SCA3, SCA6, SCA7, SCA17, and DRPLA. Besides ATXN1L, we highlight ATXN2L, ATXN3L, CACNA1B, ATXN7L1, ATXN7L2, TBPL2, and RERE as promising functional candidates to play a role in the neuropathology of the respective SCA, along with the parental gene. Although most of these duplicates lack the (CAG/CAA)n region, if functionally redundant, they may compensate for a partial loss-of-function or dysfunction of the wild-type genes in SCAs. We aim to draw attention to the hypothesis that paralogs of disease-associated genes may underlie the complex neuropathology of dominant ataxias and potentiate new therapeutic strategies.

Decreased expression of glutamate transporter GLAST in Bergmann glia is associated with the loss of Purkinje neurons in the spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is a dominantly inherited neurodegenerative disease of the cerebellum caused by a polyglutamine-repeat expansion in the protein ATXN1. We have previously demonstrated that astrocytic activation occurs early in pathogenesis, correlates with disease progression, and can occur when mutant ATXN1 expression is limited to Purkinje neurons. We now show that expression of glutamate and aspartate transporter, GLAST, is decreased in cerebellar astrocytes in a mouse model of SCA1. This decrease occurs in non-cell autonomous manner late in disease and correlates well with the loss of Purkinje neurons. Astrogliosis or decreased neuronal activity does not correlate with diminished GLAST expression. In addition, Bergmann glia remain capable of transcriptional upregulation of GLAST in response to improvement in Purkinje neurons supporting the notion of active neuron-glia crosstalk in disease.

Amyotrophic lateral sclerosis onset is influenced by the burden of rare variants in known amyotrophic lateral sclerosis genes

OBJECTIVE

To define the genetic landscape of amyotrophic lateral sclerosis (ALS) and assess the contribution of possible oligogenic inheritance, we aimed to comprehensively sequence 17 known ALS genes in 391 ALS patients from the United States.

METHODS

Targeted pooled-sample sequencing was used to identify variants in 17 ALS genes. Fragment size analysis was used to define ATXN2 and C9ORF72 expansion sizes. Genotype-phenotype correlations were made with individual variants and total burden of variants. Rare variant associations for risk of ALS were investigated at both the single variant and gene level.

RESULTS

A total of 64.3% of familial and 27.8% of sporadic subjects carried potentially pathogenic novel or rare coding variants identified by sequencing or an expanded repeat in C9ORF72 or ATXN2; 3.8% of subjects had variants in >1 ALS gene, and these individuals had disease onset 10 years earlier (p = 0.0046) than subjects with variants in a single gene. The number of potentially pathogenic coding variants did not influence disease duration or site of onset.

INTERPRETATION

Rare and potentially pathogenic variants in known ALS genes are present in >25% of apparently sporadic and 64% of familial patients, significantly higher than previous reports using less comprehensive sequencing approaches. A significant number of subjects carried variants in >1 gene, which influenced the age of symptom onset and supports oligogenic inheritance as relevant to disease pathogenesis.

Genetic testing for spinocerebellar ataxias in patients diagnosed as Parkinson's disease in Bangladesh

This study was conducted to find out Spinocerebellar Ataxias (SCA) by genetic analysis from those patients presenting with Parkinsonism in the Neurology department of Mymensingh Medical College Hospital, Bangladesh. A sample of about 5ml blood was collected by venipuncture in EDTA tube after having informed consent from each patients and healthy individual, with due Institutional Ethical committee approval for genetic study of 7 healthy people and 9 patients. The neurological disorder along with a complete physical and/or psychological, as well as family history and demographic data was recorded with a prescribed questionnaire by the neurologists of Mymensingh Medical College Hospital. Extraction of genomic DNA from the venous blood using Flexi Gene DNA kit (Qiagen, Japan) was performed in Faculty of Veterinary Science, Bangladesh Agricultural University, Mymensingh, Bangladesh. The extracted DNA was stored, accumulated and then were sent to Division of Clinical Genetics, Department of Medical Genetics, Osaka University Medical School, Suita, Osaka 565 0871, Japan for PCR and further analysis. PCR amplification of the CAG repeat was performed for the SCA1, SCA2, SCA3, SCA6 loci using primers SCA1N-F1 and SCA1N-R1, SCA2-F1 and SCA2-R1, MJDF1 and MJDR1, SCA6-F1 and SCA6-R1, respectively. SCA1 PCR of both healthy individual and suspected Parkinsons Disease (PD) patients DNA was found 250 bp (no. of CAG repeats=36). SCA2 PCR products reveal the DNA products of about 150 bp (no. of CAG repeats=23) except one patient that was suspected and it was sequenced and revealed 175bp (no. of CAG repeats=30). SCA3 PCR product size of both healthy individual and patient DNA was within 250 (no. of CAG repeats=11) to 300 bp (no. of CAG repeats=28) except one patient which was about 320 bp and its CAG repeats was about 34. SCA6 PCR product size of both healthy individual and patient DNA was about 150 bp (no. of CAG repeats=16).

Canadian Association of Neurosciences Review: Polyglutamine Expansion Neurodegenerative Diseases

Since the early 1990s, DNA triplet repeat expansions have been found to be the cause in an ever increasing number of genetic neurologic diseases. A subset of this large family of genetic diseases has the expansion of a CAG DNA triplet in the open reading frame of a coding exon. The result of this DNA expansion is the expression of expanded glutamine amino acid repeat tracts in the affected proteins, leading to the term, Polyglutamine Diseases, which is applied to this sub-family of diseases. To date, nine distinct genes are known to be linked to polyglutamine diseases, including Huntington's disease, Machado-Joseph Disease and spinobulbar muscular atrophy or Kennedy's disease. Most of the polyglutamine diseases are characterized clinically as spinocerebellar ataxias. Here we discuss recent successes and advancements in polyglutamine disease research, comparing these different diseases with a common genetic flaw at the level of molecular biology and early drug design for a family of diseases where many new research tools for these genetic disorders have been developed. Polyglutamine disease research has successfully used interdisciplinary collaborative efforts, informative multiple mouse genetic models and advanced tools of pharmaceutical industry research to potentially serve as the prototype model of therapeutic research and development for rare neurodegenerative diseases.

Chemical shift assignment of the ataxin-1 AXH domain in complex with a CIC ligand peptide

Ataxin-1 is the protein responsible for the genetically-inherited neurodegenerative disease spinocerebellar ataxia type-1 linked to the expansion of a polyglutamine tract within the protein sequence. The AXH domain of ataxin-1 is essential for the protein to function as a transcriptional co-repressor and mediates the majority of the interactions of ataxin-1 with cellular partners, mainly transcriptional regulators. One of the best characterized ataxin-1 functional partners is Capicua (CIC), a transcriptional repressor involved in signalling pathways that regulate mammalian development, tumorigenesis and, through the interaction with ataxin-1, also neurodegeneration. Complex formation of ataxin-1 with CIC is important both for the function of the wild-type protein and for pathogenesis as transcriptional disregulation is observed since the early stages of the development of the disease. Here we report the (1)H, (13)C and (15)N backbone and side-chain chemical shift assignments of the human ataxin-1 AXH domain in complex with a CIC ligand-peptide.

Intermediate CAG repeat expansion in the ATXN2 gene is a unique genetic risk factor for ALS--a systematic review and meta-analysis of observational studies

Amyotrophic lateral sclerosis (ALS) is a rare degenerative condition of the motor neurons. Over 10% of ALS cases are linked to monogenic mutations, with the remainder thought to be due to other risk factors, including environmental factors, genetic polymorphisms, and possibly gene-environmental interactions. We examined the association between ALS and an intermediate CAG repeat expansion in the ATXN2 gene using a meta-analytic approach. Observational studies were searched with relevant disease and gene terms from MEDLINE, EMBASE, and PsycINFO from January 2010 through to January 2014. All identified articles were screened using disease terms, gene terms, population information, and CAG repeat information according to PRISMA guidelines. The final list of 17 articles was further evaluated based on the study location, time period, and authors to exclude multiple usage of the same study populations: 13 relevant articles were retained for this study. The range 30-33 CAG repeats in the ATXN2 gene was most strongly associated with ALS. The meta-analysis revealed that the presence of an intermediate CAG repeat (30-33) in the ATXN2 gene was associated with an increased risk of ALS [odds ratio (OR) = 4.44, 95%CI: 2.91-6.76)] in Caucasian ALS patients. There was no significant difference in the association of this CAG intermediate repeat expansion in the ATXN2 gene between familial ALS cases (OR = 3.59, 1.58-8.17) and sporadic ALS cases (OR = 3.16, 1.88-5.32). These results indicate that the presence of intermediate CAG repeat expansion in the ATXN2 gene is a specific genetic risk factor for ALS, unlike monogenic mutations with an autosomal dominant transmission mode, which cause a more severe phenotype of ALS, with a higher prevalence in familial ALS.

Extensive molecular genetic survey of Taiwanese patients with amyotrophic lateral sclerosis

Identification of genetic mutations has been of burgeoning importance in amyotrophic lateral sclerosis (ALS) in recent years. The aim of this study was to determine the frequency and spectrum of mutations in major ALS-causing genes in a Taiwanese ALS cohort of Han Chinese origin. Mutational analyses of the SOD1, TARDBP, FUS, OPTN, VCP, UBQLN2, SQSTM1, PFN1, HNRNPA1, and HNRNPA2B1 genes were carried out by direct sequencing in 161 unrelated patients with ALS, including 30 with familial ALS (FALS) and 131 with sporadic ALS (SALS). The CAG repeat size in ATXN2 and the GGGGCC repeat expansion in C9ORF72 of the patients were also investigated. Mutations were identified in 33 patients (20.5%, 33/161), including 22 with FALS and 11 with SALS. Mutations were identified most frequently in SOD1 (7.5%). Three mutations are novel, including SOD1 p.G10A, SOD1 p.D83N, and OPTN p.L494W. These findings broaden the spectrum of ALS-causing mutations and are indispensable for designing optimal strategies of mutational analysis and genetic counseling of ALS for patients of Chinese origin.

Candidate genes and functional noncoding variants identified in a canine model of obsessive-compulsive disorder

BACKGROUND

Obsessive-compulsive disorder (OCD), a severe mental disease manifested in time-consuming repetition of behaviors, affects 1 to 3% of the human population. While highly heritable, complex genetics has hampered attempts to elucidate OCD etiology. Dogs suffer from naturally occurring compulsive disorders that closely model human OCD, manifested as an excessive repetition of normal canine behaviors that only partially responds to drug therapy. The limited diversity within dog breeds makes identifying underlying genetic factors easier.

RESULTS

We use genome-wide association of 87 Doberman Pinscher cases and 63 controls to identify genomic loci associated with OCD and sequence these regions in 8 affected dogs from high-risk breeds and 8 breed-matched controls. We find 119 variants in evolutionarily conserved sites that are specific to dogs with OCD. These case-only variants are significantly more common in high OCD risk breeds compared to breeds with no known psychiatric problems. Four genes, all with synaptic function, have the most case-only variation: neuronal cadherin (CDH2), catenin alpha2 (CTNNA2), ataxin-1 (ATXN1), and plasma glutamate carboxypeptidase (PGCP). In the 2 Mb gene desert between the cadherin genes CDH2 and DSC3, we find two different variants found only in dogs with OCD that disrupt the same highly conserved regulatory element. These variants cause significant changes in gene expression in a human neuroblastoma cell line, likely due to disrupted transcription factor binding.

CONCLUSIONS

The limited genetic diversity of dog breeds facilitates identification of genes, functional variants and regulatory pathways underlying complex psychiatric disorders that are mechanistically similar in dogs and humans.

Amyotrophic lateral sclerosis and spinocerebellar ataxia type 2 in a family with full CAG repeat expansions of ATXN2

IMPORTANCE

A family with coexistence of spinocerebellar ataxia type 2 and amyotrophic lateral sclerosis (ALS) is described.

OBSERVATIONS

Intermediate or full CAG repeat expansions of ATXN2 are associated with ALS. However, no coexistence of spinocerebellar ataxia type 2 and ALS in a family has been reported in the literature.We describe a 47-year-old woman with an 11-year history of ataxia and her paternal uncle with ALS who were evaluated at Columbia University Medical Center since July 2006. Both our patient with ataxia and her uncle with ALS have full pathological CAG repeat expansions of ATXN2.

CONCLUSIONS AND RELEVANCE

The diverse clinical phenotypes of ATXN2 CAG expansions and their coexistence in a single family are highlighted. A clinician should consider the diagnosis of spinocerebellar ataxia type 2 when encountering a patient with ataxia and a family history of ALS.

Therapeutic modulation of eIF2α phosphorylation rescues TDP-43 toxicity in amyotrophic lateral sclerosis disease models

Amyotrophic lateral sclerosis (ALS) is a fatal, late-onset neurodegenerative disease primarily affecting motor neurons. A unifying feature of many proteins associated with ALS, including TDP-43 and ataxin-2, is that they localize to stress granules. Unexpectedly, we found that genes that modulate stress granules are strong modifiers of TDP-43 toxicity in Saccharomyces cerevisiae and Drosophila melanogaster. eIF2α phosphorylation is upregulated by TDP-43 toxicity in flies, and TDP-43 interacts with a central stress granule component, polyA-binding protein (PABP). In human ALS spinal cord neurons, PABP accumulates abnormally, suggesting that prolonged stress granule dysfunction may contribute to pathogenesis. We investigated the efficacy of a small molecule inhibitor of eIF2α phosphorylation in ALS models. Treatment with this inhibitor mitigated TDP-43 toxicity in flies and mammalian neurons. These findings indicate that the dysfunction induced by prolonged stress granule formation might contribute directly to ALS and that compounds that mitigate this process may represent a novel therapeutic approach.

Silencing neurodegenerative disease: bringing RNA interference to the clinic

RNA interference (RNAi) is a recently described conserved biological pathway where non-coding RNAs suppress the expression of specific genes. Research efforts in the RNAi field aim to gain a better understanding of how its underlying machinery is orchestrated, to define the biological role of this conserved pathway, determine how to effectively manipulate RNAi in the laboratory and to integrate all this knowledge to develop novel therapies for human disease. This review summarizes the advances in the design of therapeutic RNAi for neurodegenerative diseases and discusses some of the experimental steps required to bring this therapy to human clinical trials.

A review on the cause-effect relationship between oxidative stress and toxic proteins in the pathogenesis of neurodegenerative diseases

Protein aggregates are the defining pathological feature of human neurodegenerative diseases. Studies have revealed that mutant huntingtin, polyglutamine-expanded ataxin-1 and ataxin-3 can cause elevated levels of reactive oxygen species in neuronal cells. It has also been indicated that the normal host prion protein behaves as an antioxidant, while the neurotoxic peptide based on the sequence of the scrapie isoform increases hydrogen peroxide toxicity in neuronal cultures. Additionally, not only can oxidative stress contribute to the aggregation of beta-amyloid and alpha-synuclein, but both beta-amyloid and alpha-synuclein can induce oxidative damage. Furthermore, oxidative stressors have been shown to play a critical role in neurofibrillary pathology leading to tau hyperphosphorylation. In conclusion, the present review supports a cause-effect relationship between oxidative stress and toxic proteins in the pathogenesis of neurodegenerative disorders.

Amyotrophic lateral sclerosis: an update on recent genetic insights

Amyotrophic lateral sclerosis (ALS) is a devastating neurodegenerative disease affecting both upper and lower motor neurons. The prognosis for ALS is extremely poor, but there is a limited course of treatment with only one approved medication. A most striking recent discovery is that TDP-43 is identified as a key molecule that is associated with both sporadic and familial forms of ALS. TDP-43 is not only a pathological hallmark, but also a genetic cause for ALS. Subsequently, a number of ALS-causative genes have been found. Above all, the RNA-binding protein, such as FUS, TAF15, EWSR1 and hnRNPA1, have structural and functional similarities to TDP-43, and physiological functions of some molecules, including VCP, UBQLN2, OPTN, FIG4 and SQSTM1, are involved in a protein degradation system. These discoveries provide valuable insight into the pathogenesis of ALS, and open doors for developing an effective disease-modifying therapy.

Ataxin-2 modulates the levels of Grb2 and SRC but not ras signaling

Ataxin-2 (ATXN2) is implicated mainly in mRNA processing. Some ATXN2 associates with receptor tyrosine kinases (RTK), inhibiting their endocytic internalization through interaction of proline-rich domains (PRD) in ATXN2 with SH3 motifs in Src. Gain of function of ATXN2 leads to neuronal atrophy in the diseases spinocerebellar ataxia type 2 (SCA2) and amyotrophic lateral sclerosis (ALS). Conversely, ATXN2 knockout (KO) mice show hypertrophy and insulin resistance. To elucidate the influence of ATXN2 on trophic regulation, we surveyed interactions of ATXN2 with SH3 motifs from numerous proteins and observed a novel interaction with Grb2. Direct binding in glutathione S-transferase (GST) pull-down assays and coimmunoprecipitation of the endogenous proteins indicated a physiologically relevant association. In SCA2 patient fibroblasts, Grb2 more than Src protein levels were diminished, with an upregulation of both transcripts suggesting enhanced protein turnover. In KO mouse embryonal fibroblasts (MEF), the protein levels of Grb2 and Src were decreased. ATXN2 absence by itself was insufficient to significantly change Grb2-dependent signaling for endogenous Ras levels, Ras-GTP levels, and kinetics as well as MEK1 phosphorylation, suggesting that other factors compensate for proliferation control. In KO tissue with postmitotic neurons, a significant decrease of Src protein levels is prominent rather than Grb2. ATXN2 mutations modulate the levels of several components of the RTK endocytosis complex and may thus contribute to alter cell proliferation as well as translation and growth.

Thrombotic antiphospholipid syndrome shows strong haplotypic association with SH2B3-ATXN2 locus

Background

Thrombotic antiphospholipid syndrome is defined as a complex form of thrombophilia that is developed by a fraction of antiphospholipid antibody (aPLA) carriers. Little is known about the genetic risk factors involved in thrombosis development among aPLA carriers.

Methods

To identify new loci conferring susceptibility to thrombotic antiphospholipid syndrome, a two-stage genotyping strategy was performed. In stage one, 19,000 CNV loci were genotyped in 14 thrombotic aPLA+ patients and 14 healthy controls by array-CGH. In stage two, significant CNV loci were fine-mapped in a larger cohort (85 thrombotic aPLA+, 100 non-thrombotic aPLA+ and 569 healthy controls).

Results

Array-CGH and fine-mapping analysis led to the identification of 12q24.12 locus as a new susceptibility locus for thrombotic APS. Within this region, a TAC risk haplotype comprising one SNP in SH2B3 gene (rs3184504) and two SNPs in ATXN2 gene (rs10774625 and rs653178) exhibited the strongest association with thrombotic antiphospholipid syndrome (p-value = 5,9 × 10⁻⁴ OR 95% CI 1.84 (1.32–2.55)).

Conclusion

The presence of a TAC risk haplotype in ATXN2-SH2B3 locus may contribute to increased thrombotic risk in aPLA carriers.

Assessing the efficacy of specific cerebellomodulatory drugs for use as therapy for spinocerebellar ataxia type 1

Spinocerebellar ataxias are autosomal dominant diseases, associated in some types with a CAG repeat expansion, and characterised by a progressive loss of motor function. Currently, as there is no cure for most ataxias, treatment predominantly involves physical therapy. Various symptomatic drug treatments have been tried; however, published clinical studies have provided inconsistent results, likely due to small sample sizes, mixed patient populations and insensitive or subjective assessment scales. SCA1(154Q) transgenic mice display motor function impairments and ultimately a reduced number of cerebellar Purkinje neurons-characteristics comparable to most forms of sporadic and hereditary ataxias. We monitored motor function in SCA1(154Q) mice from 5 to 20 weeks of age and assessed the efficacy of four potential cerebellar modulatory drugs in attenuating deficits in rotor-rod performance. The drugs riluzole, amantadine, zolpidem and buspirone were selected based on their different mechanisms of action and their Food and Drug Administration (FDA)/Australian Therapeutic Goods Administration approval for other indications. SCA1(154Q) and C57/Bl6 wild-type mice were administered with four ascending acute doses of each drug, over 2 days. Following each dose, mice were assesed for motor function on the accelerating rotor-rod. None of the four drugs attenuated motor deficts in SCA1(154Q) mice at any dose; at FDA equivalent and higher dose administration of zolpidem and buspirone led to sedation in both strains. Our results suggest that the aforementioned drugs are likely to be ineffective for symptomatic treatment of SCA1 and most other ataxic patients and emphasise the need for comphrehensive drug studies prior to clinical use.

A role for Drosophila ATX2 in activation of PER translation and circadian behavior

A negative transcriptional feedback loop generates circadian rhythms in Drosophila. PERIOD (PER) is a critical state-variable in this mechanism, and its abundance is tightly regulated. We found that the Drosophila homolog of ATAXIN-2 (ATX2)--an RNA-binding protein implicated in human neurodegenerative diseases--was required for circadian locomotor behavior. ATX2 was necessary for PER accumulation in circadian pacemaker neurons and thus determined period length of circadian behavior. ATX2 was required for the function of TWENTY-FOUR (TYF), a crucial activator of PER translation. ATX2 formed a complex with TYF and promoted its interaction with polyadenylate-binding protein (PABP). Our work uncovers a role for ATX2 in circadian timing and reveals that this protein functions as an activator of PER translation in circadian neurons.

Genome-wide association study of a quantitative disordered gambling trait

Disordered gambling is a moderately heritable trait, but the underlying genetic basis is largely unknown. We performed a genome-wide association study (GWAS) for disordered gambling using a quantitative factor score in 1312 twins from 894 Australian families. Association was conducted for 2 381 914 single-nucleotide polymorphisms (SNPs) using the family-based association test in Merlin followed by gene and pathway enrichment analyses. Although no SNP reached genome-wide significance, six achieved P-values < 1 × 10(-5) with variants in three genes (MT1X, ATXN1 and VLDLR) implicated in disordered gambling. Secondary case-control analyses found two SNPs on chromosome 9 (rs1106076 and rs12305135 near VLDLR) and rs10812227 near FZD10 on chromosome 12 to be significantly associated with lifetime Diagnostic and Statistical Manual of Mental Disorders, fourth edition pathological gambling and South Oaks Gambling Screen classified probable pathological gambling status. Furthermore, several addiction-related pathways were enriched for SNPs associated with disordered gambling. Finally, gene-based analysis of 24 candidate genes for dopamine agonist-induced gambling in individuals with Parkinson's disease suggested an enrichment of SNPs associated with disordered gambling. We report the first GWAS of disordered gambling. While further replication is required, the identification of susceptibility loci and biological pathways will be important in characterizing the biological mechanisms that underpin disordered gambling.

Regulation of ataxin-1 phosphorylation and its impact on biology

Ataxin-1 protein expression is found in the cytoplasm and nucleus of Purkinje cells, the primary site of spinocerebellar ataxia type 1 (SCA1). Phosphorylation at S776 occurs in the cytoplasm and stabilizes the protein through interaction with 14-3-3, allowing it to translocate into the nucleus where disease is initiated. Phosphorylation and stabilization are enhanced when the polyglutamine expansion is present. In this chapter, we present a model of neurodegeneration in SCA1 initiated through phosphorylation at S776 by cAMP-dependent protein kinase (PKA) and enhanced by the presence of the polyglutamine expansion. The biological methods used to uncover SCA1 pathogenesis and phosphorylation at S776 are described.

Ataxin-2-like is a regulator of stress granules and processing bodies

Paralogs for several proteins implicated in neurodegenerative disorders have been identified and explored to further facilitate the identification of molecular mechanisms contributing to disease pathogenesis. For the disease-causing protein in spinocerebellar ataxia type 2, ataxin-2, a paralog of unknown function, termed ataxin-2-like, has been described. We discovered that ataxin-2-like associates with known interaction partners of ataxin-2, the RNA helicase DDX6 and the poly(A)-binding protein, and with ataxin-2 itself. Furthermore, we found that ataxin-2-like is a component of stress granules. Interestingly, sole ataxin-2-like overexpression led to the induction of stress granules, while a reduction of stress granules was detected in case of a low ataxin-2-like level. Finally, we observed that overexpression of ataxin-2-like as well as its reduction has an impact on the presence of microscopically visible processing bodies. Thus, our results imply a functional overlap between ataxin-2-like and ataxin-2, and further indicate a role for ataxin-2-like in the regulation of stress granules and processing bodies.

ATXN2-CAG42 sequesters PABPC1 into insolubility and induces FBXW8 in cerebellum of old ataxic knock-in mice

Spinocerebellar Ataxia Type 2 (SCA2) is caused by expansion of a polyglutamine encoding triplet repeat in the human ATXN2 gene beyond (CAG)₃₁. This is thought to mediate toxic gain-of-function by protein aggregation and to affect RNA processing, resulting in degenerative processes affecting preferentially cerebellar neurons. As a faithful animal model, we generated a knock-in mouse replacing the single CAG of murine Atxn2 with CAG42, a frequent patient genotype. This expansion size was inherited stably. The mice showed phenotypes with reduced weight and later motor incoordination. Although brain Atxn2 mRNA became elevated, soluble ATXN2 protein levels diminished over time, which might explain partial loss-of-function effects. Deficits in soluble ATXN2 protein correlated with the appearance of insoluble ATXN2, a progressive feature in cerebellum possibly reflecting toxic gains-of-function. Since in vitro ATXN2 overexpression was known to reduce levels of its protein interactor PABPC1, we studied expansion effects on PABPC1. In cortex, PABPC1 transcript and soluble and insoluble protein levels were increased. In the more vulnerable cerebellum, the progressive insolubility of PABPC1 was accompanied by decreased soluble protein levels, with PABPC1 mRNA showing no compensatory increase. The sequestration of PABPC1 into insolubility by ATXN2 function gains was validated in human cell culture. To understand consequences on mRNA processing, transcriptome profiles at medium and old age in three different tissues were studied and demonstrated a selective induction of Fbxw8 in the old cerebellum. Fbxw8 is encoded next to the Atxn2 locus and was shown in vitro to decrease the level of expanded insoluble ATXN2 protein. In conclusion, our data support the concept that expanded ATXN2 undergoes progressive insolubility and affects PABPC1 by a toxic gain-of-function mechanism with tissue-specific effects, which may be partially alleviated by the induction of FBXW8.

Frequent age-associated neurodegenerative disorders like Alzheimer's, Parkinson's, and Lou Gehrig's disease are being elucidated molecularly by studying rare heritable variants. Various hereditary neurodegenerative disorders are caused by polyglutamine expansions in different proteins. In spite of this common pathogenesis and the pathological aggregation of most affected proteins, investigators were puzzled that the pattern of affected neuron population varies and that molecular mechanisms seem different between such disorders. The polyglutamine expansions in the Ataxin-2 (ATXN2) protein are exceptional in view of the lack of aggregate clumps in nuclei of affected Purkinje neurons and well documented alterations of RNA processing in the resulting disorders SCA2 and ALS. Here, as a faithful disease model and to overcome the unavailability of autopsied patient brain tissues, we generated and characterized an ATXN2-CAG42-knock-in mouse mutant. Our data show that the unspecific, chronically present mutation leads to progressive insolubility and to reduced soluble levels of the disease protein and of an interactor protein, which modulates RNA processing. Compensatory efforts are particularly weak in vulnerable tissue. They appear to include the increased degradation of the toxic disease protein by FBXW8. Thus the link between protein and RNA pathology becomes clear, and crucial molecular targets for preventive therapy are identified.

ATXN2 and its neighbouring gene SH2B3 are associated with increased ALS risk in the Turkish population

Expansions of the polyglutamine (polyQ) domain (≥ 34) in Ataxin-2 (ATXN2) are the primary cause of spinocerebellar ataxia type 2 (SCA2). Recent studies reported that intermediate-length (27-33) expansions increase the risk of Amyotrophic Lateral Sclerosis (ALS) in 1-4% of cases in diverse populations. This study investigates the Turkish population with respect to ALS risk, genotyping 158 sporadic, 78 familial patients and 420 neurologically healthy controls. We re-assessed the effect of ATXN2 expansions and extended the analysis for the first time to cover the ATXN2 locus with 18 Single Nucleotide Polymorphisms (SNPs) and their haplotypes. In accordance with other studies, our results confirmed that 31-32 polyQ repeats in the ATXN2 gene are associated with risk of developing ALS in 1.7% of the Turkish ALS cohort (p=0.0172). Additionally, a significant association of a 136 kb haplotype block across the ATXN2 and SH2B3 genes was found in 19.4% of a subset of our ALS cohort and in 10.1% of the controls (p=0.0057, OR: 2.23). ATXN2 and SH2B3 encode proteins that both interact with growth receptor tyrosine kinases. Our novel observations suggest that genotyping of SNPs at this locus may be useful for the study of ALS risk in a high percentage of individuals and that ATXN2 and SH2B3 variants may interact in modulating the disease pathway.

Identification of human proteins that modify misfolding and proteotoxicity of pathogenic ataxin-1

Proteins with long, pathogenic polyglutamine (polyQ) sequences have an enhanced propensity to spontaneously misfold and self-assemble into insoluble protein aggregates. Here, we have identified 21 human proteins that influence polyQ-induced ataxin-1 misfolding and proteotoxicity in cell model systems. By analyzing the protein sequences of these modifiers, we discovered a recurrent presence of coiled-coil (CC) domains in ataxin-1 toxicity enhancers, while such domains were not present in suppressors. This suggests that CC domains contribute to the aggregation- and toxicity-promoting effects of modifiers in mammalian cells. We found that the ataxin-1-interacting protein MED15, computationally predicted to possess an N-terminal CC domain, enhances spontaneous ataxin-1 aggregation in cell-based assays, while no such effect was observed with the truncated protein MED15ΔCC, lacking such a domain. Studies with recombinant proteins confirmed these results and demonstrated that the N-terminal CC domain of MED15 (MED15CC) per se is sufficient to promote spontaneous ataxin-1 aggregation in vitro. Moreover, we observed that a hybrid Pum1 protein harboring the MED15CC domain promotes ataxin-1 aggregation in cell model systems. In strong contrast, wild-type Pum1 lacking a CC domain did not stimulate ataxin-1 polymerization. These results suggest that proteins with CC domains are potent enhancers of polyQ-mediated protein misfolding and aggregation in vitro and in vivo.

FOX-2 dependent splicing of ataxin-2 transcript is affected by ataxin-1 overexpression

Alternative splicing is a fundamental posttranscriptional mechanism for controlling gene expression, and splicing defects have been linked to various human disorders. The splicing factor FOX-2 is part of a main protein interaction hub in a network related to human inherited ataxias, however, its impact remains to be elucidated. Here, we focused on the reported interaction between FOX-2 and ataxin-1, the disease-causing protein in spinocerebellar ataxia type 1. In this line, we further evaluated this interaction by yeast-2-hybrid analyses and co-immunoprecipitation experiments in mammalian cells. Interestingly, we discovered that FOX-2 localization and splicing activity is affected in the presence of nuclear ataxin-1 inclusions. Moreover, we observed that FOX-2 directly interacts with ataxin-2, a protein modulating spinocerebellar ataxia type 1 pathogenesis. Finally, we provide evidence that splicing of pre-mRNA of ataxin-2 depends on FOX-2 activity, since reduction of FOX-2 levels led to increased skipping of exon 18 in ataxin-2 transcripts. Most striking, we observed that ataxin-1 overexpression has an effect on this splicing event as well. Thus, our results demonstrate that FOX-2 is involved in splicing of ataxin-2 transcripts and that this splicing event is altered by overexpression of ataxin-1.

Eccentric exercise facilitates mesenchymal stem cell appearance in skeletal muscle

Eccentric, or lengthening, contractions result in injury and subsequently stimulate the activation and proliferation of satellite stem cells which are important for skeletal muscle regeneration. The discovery of alternative myogenic progenitors in skeletal muscle raises the question as to whether stem cells other than satellite cells accumulate in muscle in response to exercise and contribute to post-exercise repair and/or growth. In this study, stem cell antigen-1 (Sca-1) positive, non-hematopoetic (CD45^-) cells were evaluated in wild type (WT) and α7 integrin transgenic (α7Tg) mouse muscle, which is resistant to injury yet liable to strain, 24 hr following a single bout of eccentric exercise. Sca-1⁺CD45⁻ stem cells were increased 2-fold in WT muscle post-exercise. The α7 integrin regulated the presence of Sca-1⁺ cells, with expansion occurring in α7Tg muscle and minimal cells present in muscle lacking the α7 integrin. Sca-1⁺CD45⁻ cells isolated from α7Tg muscle following exercise were characterized as mesenchymal-like stem cells (mMSCs), predominantly pericytes. In vitro multiaxial strain upregulated mMSC stem cells markers in the presence of laminin, but not gelatin, identifying a potential mechanistic basis for the accumulation of these cells in muscle following exercise. Transplantation of DiI-labeled mMSCs into WT muscle increased Pax7⁺ cells and facilitated formation of eMHC⁺DiI⁻ fibers. This study provides the first demonstration that mMSCs rapidly appear in skeletal muscle in an α7 integrin dependent manner post-exercise, revealing an early event that may be necessary for effective repair and/or growth following exercise. The results from this study also support a role for the α7 integrin and/or mMSCs in molecular- and cellular-based therapeutic strategies that can effectively combat disuse muscle atrophy.

Oxidative stress as a cofactor in spinocerebellar ataxia type 2

Spinocerebellar ataxia type 2 (SCA2) is a redox-sensitive neurodegenerative disease affecting the cerebellum, fibre connections in the cerebellum, the peripheral nervous system, and extracerebellar central pathways. Currently, Cuba has the highest reported global rate for this disease. The aim of this review article is to summarize and discuss the current knowledge about evidence of oxidative stress during SCA2. Recent reports have suggested that ataxin 2 and other related factors contribute to the redox imbalance in this disease. It is important to recognize and clarify the molecular mechanisms associated with the redox imbalance to consider ataxias innovative approaches to counteract oxidative stress-induced tissue damage, through alternative therapeutic or nutritional intervention in SCA2 and related diseases.

Transient activation of hematopoietic stem and progenitor cells by IFNγ during acute bacterial infection

How hematopoietic stem cells (HSCs) respond to inflammatory signals during infections is not well understood. Our studies have used a murine model of ehrlichiosis, an emerging tick-born disease, to address how infection impacts hematopoietic function. Infection of C57BL/6 mice with the intracellular bacterium, Ehrlichia muris, results in anemia and thrombocytopenia, similar to what is observed in human ehrlichiosis patients. In the mouse, infection promotes myelopoiesis, a process that is critically dependent on interferon gamma (IFNγ) signaling. In the present study, we demonstrate that E. muris infection also drives the transient proliferation and expansion of bone marrow Lin-negative Sca-1⁺ cKit⁺ (LSK) cells, a population of progenitor cells that contains HSCs. Expansion of the LSK population in the bone marrow was associated with a loss of dormant, long-term repopulating HSCs, reduced engraftment, and a bias towards myeloid lineage differentiation within that population. The reduced engraftment and myeloid bias of the infection-induced LSK cells was transient, and was most pronounced on day 8 post-infection. The infection-induced changes were accompanied by an expansion of more differentiated multipotent progenitor cells, and required IFNγ signaling. Thus, in response to inflammatory signals elicited during acute infection, HSCs can undergo a rapid, IFNγ-dependent, transient shift from dormancy to activity, ostensibly, to provide the host with additional or better-armed innate cells for host defense. Similar changes in hematopoietic function likely underlie many different infections of public health importance.

Xpa deficiency reduces CAG trinucleotide repeat instability in neuronal tissues in a mouse model of SCA1

Expansion of trinucleotide repeats (TNRs) is responsible for a number of human neurodegenerative disorders. The molecular mechanisms that underlie TNR instability in humans are not clear. Based on results from model systems, several mechanisms for instability have been proposed, all of which focus on the ability of TNRs to form alternative structures during normal DNA transactions, including replication, DNA repair and transcription. These abnormal structures are thought to trigger changes in TNR length. We have previously shown that transcription-induced TNR instability in cultured human cells depends on several genes known to be involved in transcription-coupled nucleotide excision repair (NER). We hypothesized that NER normally functions to destabilize expanded TNRs. To test this hypothesis, we bred an Xpa null allele, which eliminates NER, into the TNR mouse model for spinocerebellar ataxia type 1 (SCA1), which carries an expanded CAG repeat tract at the endogenous mouse Sca1 locus. We find that Xpa deficiency does not substantially affect TNR instability in either the male or female germline; however, it dramatically reduces CAG repeat instability in neuronal tissues-striatum, hippocampus and cerebral cortex-but does not alter CAG instability in kidney or liver. The tissue-specific effect of Xpa deficiency represents a novel finding; it suggests that tissue-to-tissue variation in CAG repeat instability arises, in part, by different underlying mechanisms. These results validate our original findings in cultured human cells and suggest that transcription may induce NER-dependent TNR instability in neuronal tissues in humans.

Targeting several CAG expansion diseases by a single antisense oligonucleotide

To date there are 9 known diseases caused by an expanded polyglutamine repeat, with the most prevalent being Huntington's disease. Huntington's disease is a progressive autosomal dominant neurodegenerative disorder for which currently no therapy is available. It is caused by a CAG repeat expansion in the HTT gene, which results in an expansion of a glutamine stretch at the N-terminal end of the huntingtin protein. This polyglutamine expansion plays a central role in the disease and results in the accumulation of cytoplasmic and nuclear aggregates. Here, we make use of modified 2'-O-methyl phosphorothioate (CUG)n triplet-repeat antisense oligonucleotides to effectively reduce mutant huntingtin transcript and protein levels in patient-derived Huntington's disease fibroblasts and lymphoblasts. The most effective antisense oligonucleotide, (CUG)(7), also reduced mutant ataxin-1 and ataxin-3 mRNA levels in spinocerebellar ataxia 1 and 3, respectively, and atrophin-1 in dentatorubral-pallidoluysian atrophy patient derived fibroblasts. This antisense oligonucleotide is not only a promising therapeutic tool to reduce mutant huntingtin levels in Huntington's disease but our results in spinocerebellar ataxia and dentatorubral-pallidoluysian atrophy cells suggest that this could also be applicable to other polyglutamine expansion disorders as well.

[Variation of CAG repeats in coding region of ATXN2 gene in different ethnic groups]

Toinvestigate CAG repeats variation of ATXN2 gene coding region in six ethnic groups that live in comparatively different environments, to evaluate whether these variations are under positive selection, and to find factors driving selection effects, 291 unrelated healthy individuals were collected from six ethnic groups and their STR geneotyping was performed. The frequencies of alleles and genotypes were counted and thereby Slatkin's linearized Fst values were calculated. The UPGMA tree against this gene was constructed. The MDS analysis among these groups was carried out as well. The results from the linearized Fst values indicated that there were significant evolutionary differences of the STR in ATXN2 gene between Hui and Yi groups, but not among the other 4 groups. Further analysis was performed by combining our data with published data obtained from other groups. These results indicated that there were significant differences between Japanese and other groups including Hui, Hani, Yunnan Mongolian, and Inner Mongolian. Both Hui and Mongolian from Inner Mongolia were significantly different from Han. In conclusion, the six ethnic groups had their own distribution characterizations of allelic frequencies of ATXN2 STR, and the potential cause of frequency changes in rare alleles could be the consequence of positive selection.

PolyQ repeat expansions in ATXN2 associated with ALS are CAA interrupted repeats

Amyotrophic lateral sclerosis (ALS) is a devastating, rapidly progressive disease leading to paralysis and death. Recently, intermediate length polyglutamine (polyQ) repeats of 27-33 in ATAXIN-2 (ATXN2), encoding the ATXN2 protein, were found to increase risk for ALS. In ATXN2, polyQ expansions of ≥ 34, which are pure CAG repeat expansions, cause spinocerebellar ataxia type 2. However, similar length expansions that are interrupted with other codons, can present atypically with parkinsonism, suggesting that configuration of the repeat sequence plays an important role in disease manifestation in ATXN2 polyQ expansion diseases. Here we determined whether the expansions in ATXN2 associated with ALS were pure or interrupted CAG repeats, and defined single nucleotide polymorphisms (SNPs) rs695871 and rs695872 in exon 1 of the gene, to assess haplotype association. We found that the expanded repeat alleles of 40 ALS patients and 9 long-repeat length controls were all interrupted, bearing 1-3 CAA codons within the CAG repeat. 21/21 expanded ALS chromosomes with 3CAA interruptions arose from one haplotype (GT), while 18/19 expanded ALS chromosomes with <3CAA interruptions arose from a different haplotype (CC). Moreover, age of disease onset was significantly earlier in patients bearing 3 interruptions vs fewer, and was distinct between haplotypes. These results indicate that CAG repeat expansions in ATXN2 associated with ALS are uniformly interrupted repeats and that the nature of the repeat sequence and haplotype, as well as length of polyQ repeat, may play a role in the neurological effect conferred by expansions in ATXN2.

Three spinocerebellar ataxia type 2 siblings with ataxia, parkinsonism, and motor neuronopathy

Spinocerebellar ataxia type 2 (SCA2) represents a family of dominant neurodegenerative disorders that results from CAG expansion repeat mutations. The phenotype consists of some common features, most notably progressive ataxia. We describe three siblings with SCA2, manifesting parkinsonism and ataxia in the first sibling, juvenile parkinsonism in the second and motor neuronopathy in the third. Genetic examination revealed expansion to 42, 43, and 42 CAG repeats. There was no relationship between the number of repeats and phenotype. The SCA2 gene should be studied in families with heterogeneous neurodegenerative disorders, including motor neuron disease.

Dopamine D2 receptor signaling modulates mutant ataxin-1 S776 phosphorylation and aggregation

Spinocerebellar ataxia 1 (SCA1) is a dominantly inherited neurodegenerative disease associated with progressive ataxia resulting from the loss of cerebellar Purkinje cells (PCs) and neurons in the brainstem. In PCs of SCA1 transgenic mice, the disease causing ataxin-1 protein mediates the formation of S100B containing cytoplasmic vacuoles and further self-aggregates to form intranuclear inclusions. The exact function of the ataxin-1 protein is not fully understood. However, the aggregation and neurotoxicity of the mutant ataxin-1 protein is dependent on the phosphorylation at serine 776 (S776). Although protein kinase A (PKA) has been implicated as the S776 kinase, the mechanism of PKA/ataxin-1 regulation in SCA1 is still not clear. We propose that a dopamine D(2) receptor (D2R)/S100B pathway may be involved in modulating PKA activity in PCs. Using a D2R/S100B HEK stable cell line transiently transfected with GFP-ataxin-1[82Q], we demonstrate that stimulation of the D2R/S100B pathway caused a reduction in mutant ataxin-1 S776 phosphorylation and ataxin-1 aggregation. Activation of PKA by forskolin resulted in an enhanced S776 phosphorylation and increased ataxin-1 nuclear aggregation, which was suppressed by treatment with D2R agonist bromocriptine and PKA inhibitor H89. Furthermore, treating SCA1 transgenic PC slice cultures with forskolin induced neurodegenerative morphological abnormalities in PC dendrites consistent with those observed in vivo. Taken together our data support a mechanism where PKA dependent mutant ataxin-1 phosphorylation and aggregation can be regulated by D2R/S100B signaling.

[Simulation of the distribution of spinocerebellar ataxia type 1 in Yakut populations: model parameters and results of simulation]

Demographic and clinical genetic parameters used for simulation modeling of the prevalence of spinocerebellar ataxia type 1 (SCA1) in Yakut populations are described. Demographic parameters of simulated populations and the clinical genetic characteristics of carriers of the SCA1 mutant allele in them have been compared with actual data on Abyisky and Ust-Aldansky uluses of the Republic of Sakha (Yakutia). The results of a series of simulation experiments (without migration or spontaneous mutagenesis) agree with the conclusion that the high prevalence of rate of spinocerebellar ataxia type 1 in Yakut populations may be maintained because of their specific demographic structure. Prediction of the disease prevalence has shown that it will take about 1290 years for natural selection to eliminate the mutation from the population. If medical genetic counseling (MGC) is offered to 1% of the carriers of the mutation, this period will be reduced to 200 years.

[Autopsy case of SCA2 with Parkinsonian phenotype]

This is the first autopsy case of SCA2 with parkinsonian phenotype. At the age of 46, the patient got symptoms of parkinsonism to which anti-parkinsonian drugs were effective. He had mosaic 38, 40 CAG repeat expansions on chromosome 12q23-24, being diagnosed as SCA2, and his mother and his son also had CAG expansions on the same locus. In addition to parkinsonism, he also exhibited autonomic disturbance, dementia, and mild cerebellar ataxia Brain images revealed severe atrophy of pons and medulla oblongata, resembling MSA-C. HVA and 5-HIAA were reduced in the cerebrospinal fluid, and the heart-mediastinum (H/M) ratio in myocardial 123I-MIBG cintigram was decreased, which suggested Lewy body pathology. He died at the age of 75 and the autopsy revealed atrophy of the olivo-ponto-cerebellar (OPC) system and substantia nigra which was compatible to SCA2, although the OPC system atrophy was less severe than formerly reported SCA2 cases. The degrees of atrophy of the OPC system and substantia nigra might explain the predominancy of clinical symptoms. Anti-1C2 positive inclusions in the pontine nuclei, inferior olive nuclei, cerebellum and substantia nigra confirmed a polyglutamine disease. In addition, there were the anti-phosphorylated alpha-synuclein positive, Lewy body related pathological changes in the substantia nigra, the locus ceruleus, the dorsal motor nuclei of vagus, and the sympathetic nerve in the myocardium. Major genetic abnormalities related to Parkinson disease were not detected. As another case of SCA2 with Lewy body pathology was reported in Japan, the coexistence of SCA2 and Lewy body pathology may not be accidental. Since myocardial MIBG scincigram can predict Lewy body pathology, we should seek more clinical cases of SCA2 with Lewy body pathology.

Ataxin active site determination using spectral distribution of electron ion interaction potentials of amino acids

Ataxia is a genetic neurological disorder characterised by a neurodegenerative process affecting a motor cortex responsible for balance and coordination. Recently several genes that cause autosomal dominant ataxia development were identified. These abnormal genes share a common ability to produce abnormal ataxin proteins that can affect nerve cells in the cerebellum and spinal cord. Here, using the Resonant Recognition Model (RRM) based on signal processing, we analysed ataxin proteins and identified the characteristic features corresponding to their biological activities. The RRM is a physico-mathematical model developed for analysis of protein interactions. By incorporating Smoothed Pseudo Wigner-Ville distribution (SPWV) in the RRM, we can define the active regions along the protein molecule. The results showed that our computational predictions correspond closely with the experimentally identified locations of the active/binding sites for ataxin-1 and ataxin-3 protein groups. The results obtained provide a valuable insight into the functional performance of ataxin proteins.

Progression markers of Spinocerebellar ataxia 2. A twenty years neurophysiological follow up study

Nerve conduction is profoundly affected in Spinocerebellar ataxia 2 (SCA2) even before the onset of the disease, but there is no information regarding its progression to the final stage of SCA2. In order to study the progression patterns of nerve conduction abnormalities in SCA2 we performed a prospective follow up evaluation of sensory and motor conduction in 21 SCA2 mutation carriers-initially presymptomatics- and 19 non-SCA2 mutation carriers during 20years. The earliest electrophysiological alterations were the reduction of sensory amplitudes in median and sural nerves, which could be found 8 to 5years prior disease onset and in the last 4years of the preclinical stage respectively. These abnormalities were followed by the increase of sensory latencies and decrease of conduction velocities. Sensory amplitudes progressively decreased during the follow-up clinical stage, rendering almost all patients with abnormal amplitudes and lack of sensory potentials, with faster progression rates in patients with larger CAG repeat lengths. Peripheral motor nerves showed the later involvement. These findings were used to define three distinct stages that describe the progression of the peripheral neuropathy. We suggest that sensory amplitudes could be useful biomarkers to assess the progression of peripheral nerve involvement and therefore to evaluate future clinical trials of therapeutic agents.

Phosphorylation of S776 and 14-3-3 binding modulate ataxin-1 interaction with splicing factors

Ataxin-1 (Atx1), a member of the polyglutamine (polyQ) expanded protein family, is responsible for spinocerebellar ataxia type 1. Requirements for developing the disease are polyQ expansion, nuclear localization and phosphorylation of S776. Using a combination of bioinformatics, cell and structural biology approaches, we have identified a UHM ligand motif (ULM), present in proteins associated with splicing, in the C-terminus of Atx1 and shown that Atx1 interacts with and influences the function of the splicing factor U2AF65 via this motif. ULM comprises S776 of Atx1 and overlaps with a nuclear localization signal and a 14-3-3 binding motif. We demonstrate that phosphorylation of S776 provides the molecular switch which discriminates between 14-3-3 and components of the spliceosome. We also show that an S776D Atx1 mutant previously designed to mimic phosphorylation is unsuitable for this aim because of the different chemical properties of the two groups. Our results indicate that Atx1 is part of a complex network of interactions with splicing factors and suggest that development of the pathology is the consequence of a competition of aggregation with native interactions. Studies of the interactions formed by non-expanded Atx1 thus provide valuable hints for understanding both the function of the non-pathologic protein and the causes of the disease.

[Studies on the CAG repeat expansion in patients with hereditary spinocerebellar ataxia from Chinese Han]

OBJECTIVE

To investigate the CAG trinucleotide repeat expansion in spinocerebellar ataxia (SCA) types 1, 2, 3, 6, 7, 12, and 17 from Chinese Han.

METHODS

The pathological CAG triplet repeat expansions of the SCA1, SCA2, SCA3/Machado-Joseph disease (MJD), SCA6, SCA7, SCA12 and SCA17 genes were analyzed in a cohort of 559 Mainland Chinese patients affected by spinocerebellar ataxia, including 363 probands from families with autosomal dominant SCA and 196 sporadic cases. Polymerase chain reaction, agarose gel electrophoresis, recombinant DNA technology by T-vector cloning and direct sequencing were performed to detect the CAG-repeat number of abnormal allele.

RESULTS

Among the 559 SCA patients, twenty-three were positive for SCA1, the ranges of expanded CAG repeats were from 39 to 60 (mean:51.09+/-4.88); thirty-two were positive for SCA2, the ranges of expanded CAG repeats were from 36 to 51 (mean:40.34+/-4.40); three hundred and five were positive for SCA3/MJD, the ranges of expanded CAG repeats were from 49 to 86 (mean:73.84+/-5.07); nine were positive for SCA6, the ranges of expanded CAG repeats were from 23 to 29 (mean:25.56+/-1.94); twenty-seven were positive for SCA7, the ranges of expanded CAG repeats were from 38 to 71(mean:58.22+/-10.90); three were positive for SCA12, the ranges of expanded CAG repeats were from 51 to 52 (mean:51.33+/-0.58); and finally, two were positive for SCA17, the range of expanded CAG repeats were from 53 to 55 (mean:54.00+/-1.41).

CONCLUSION

The 39 CAG repeats of SCA1, 49 CAG repeats of SCA3 and 51 CAG repeats of SCA12 are all the shortest known causative expanded alleles, while the 86 CAG repeats of SCA3/MJD is the largest full expanded allele that has never been reported. Furthermore, it is the first report of SCA17 subtype in Mainland Chinese and first research that established the abnormal reference standard of CAG repeat number of different subtypes of SCA in Chinese Han.

[Copy number variation of trinucleotide repeat in dynamic mutation sites of autosomal dominant cerebellar ataxias related genes]

OBJECTIVE

To standardize the experimental procedure of the gene test for autosomal dominant cerebellar ataxias (ADCA), and provide the basis for quantitative criteria of the dynamic mutation of spinocerebellar ataxia (SCA) genes in Chinese population.

METHODS

Genotyping of the dynamic mutation loci of the SCA1, SCA2, SCA3, SCA6 and SCA7 genes was performed, using florescence PCR-capillary electrophoresis followed by DNA sequencing, to investigate the variation range of copy number of CAG tandem repeat of the genes in 263 probands of ADCA pedigrees and 261 non-related normal controls. Based on the sequencing result, the bias of the CAG copy number estimation using capillary electrophoresis with different DNA controls was compared to analyze the technical detailes of the electrophresis method in testing the dynamic mutation sites.

RESULTS

PCR products containing dynamic mutation loci of the SCA genes showed significantly higher mobility than that of molecular weigh marker with relatively balanced GC content. This was particularly obvious in the SCA2, SCA 6 and SCA7 genes whereas the deviation of copy number could be corrected to +/-1 when known CAG copy number fragments were used as controls. The mobility of PCR products was primarily related to the copy number of CAG repeat when the fragments contained normal CAG repeat. In the 263 ADCA pedigrees, 6 (2.28%) carried SCA1 gene mutation, 8 (3.04%) had SCA2 mutation and 81 (30.80%) harbored SCA3 mutation. The gene mutation of SCA6 and SCA7 was not found. The normal variation range of the CAG repeat was 17-36 copies in SCA1 gene, 13-30 copies in SCA2, 14-39 copies in SCA3, 6-16 copies in SCA6 and 6-13 copies in SCA7. The heterozygosity was 76.1%, 17.7%, 74.4%, 72.1% and 41.3%, respectively. The mutation range of the CAG repeat was 49-56 copies in SCA1 gene, 36-41 copies in SCA2, 59-81 copies in SCA3. Neither homozygous mutation of an SCA gene nor double heterozygous mutation of the SCA genes was observed in the study.

CONCLUSION

The copy number of the CAG repeat in SCA genes could be calculated accurately based on the result of florescence PCR-capillary electrophoresis when limited amount of known repeat copy number controls were used. Our result supported that the notion that SCA3 gene mutation was the most common cause for ADCA, and the obtained data would be helpful for establishing quantitative criteria of the dynamic mutation of the SCA genes in Chinese.

Very small embryonic-like stem cells are present in adult murine organs: ImageStream-based morphological analysis and distribution studies

Recently, we purified a population of CXCR4+/Oct-4+/SSEA-1+/Sca-1+/Lin(-)/CD45(-) very small embryonic-like stem cells (VSELs) from adult murine bone marrow (BM). After using flow cytometry, ImageStream analysis, confocal microscopy, and real time RT-PCR, we report that similar cells could be also identified and isolated from several organs in adult mice. The highest total numbers of Oct-4+ VSELs were found in the brain, kidneys, muscles, pancreas, and BM. These observations support our hypothesis that a population of very primitive cells expressing germ line/epiblast markers (Oct-4, SSEA-1) is deposited early during embryogenesis in various organs and survives into adulthood. Further studies are needed to determine whether these cells, after being isolated from various adult human organs similarly to their murine BM-derived counterparts, are endowed with pluripotent stem cell properties.