Quantitative genetic variation in the hematopoietic stem cell and progenitor cell compartment and in lifespan are closely linked at multiple loci in BXD recombinant inbred mice

The number of bone marrow hematopoietic stem and progenitor cells as defined by the lineage(-), Sca1(++), c-kit(+) (LSK) phenotype and their proliferative capacity in vitro are subject to quantitative genetic variation, and several quantitative trait loci (QTL) have been identified in young mice. Because some traits affecting hematopoiesis also change with age in a mouse strain-dependent fashion, we performed quantitative trait analysis in aged BXD recombinant inbred (RI) mice for the number and frequency of LSK cells, and for their proliferative capacity in vitro. Several novel QTL were identified. The number and frequency of LSK cells in old mice correlated inversely with lifespan. Furthermore, 4 of 7 lifespan QTL overlap with QTL contributing to the number, frequency, or proliferative capacity of LSK cells in young or old mice. Taken together, these data establish a close genetic, and perhaps functional, link between genetic variation in lifespan and characteristics of stem and progenitor cells.

General transcriptional repression by polyglutamine disease proteins is not directly linked to the presence of inclusion bodies

By using direct immunocytochemistry of BrU incorporated to RNA in the nuclei, we evaluated the effect of mutant huntingtin and ataxin-1 on general transcription in primary cortical and cerebellar neurons. Our quantitative analyses clearly showed that these mutant polyglutamine disease proteins repress general transcription. In addition, we found that general transcription level was almost similar in inclusion body-positive and -negative neurons. The result suggests that presence of inclusion body is not essential for repressing general transcription in contrast to its reported role for suppressing specific gene transcription in the polyglutamine disease pathology.

[Analysis and application of SCA1 and SCA3/MJD gene CAG repeats in Han population in Northeastern China]

OBJECTIVE

To investigate the normal range of (CAG)n in spinocerebellar ataxia type 1 (SCA1) gene and spinocerebellar ataxia type 3 (SCA3/MJD) gene in 110 normal subjects of Han population in Northeastern China, to assess the genotypes for clinically diagnosed spinocerebellar ataxia(SCA) individuals including 25 patients from 8 families and 6 sporadic patients, and to make presymptomatic and prenatal diagnosis.

METHODS

DNA fragments from the normal subjects and the patients were detected by fluorescence-PCR. Homozygosities were selected for DNA sequencing.

RESULTS

The normal ranges of (CAG)n of SCA1 and SCA3/MJD were 20-39 and 14-38 repeats respectively, SCA1 was found mostly to be 26 and 27 repeats, allele frequency 34.09% and 20.91%; heterozygosity was 84.55%, SCA3/MJD was found mostly to be 14 repeats, allele frequency 39.55%, heterozygosity was 78.18%.(CAG)(68) of SCA3/MJD gene of one affected individual had been found in a family but no CAG mutative expansion in related members was observed.

CONCLUSION

The normal ranges of CAG repeats vary with areas and races. SCAs genotyping is the first choice in presymptomatic and prenatal diagnosis.

Dynamic mutation and human disorders: the spinocerebellar ataxias (review)

A completely new mutational event associated with human diseases - the dynamic mutation - was discovered in the last decade. The molecular mechanism underlying dynamic mutation involves the expansion and intergenerational instability of a tandem-arrayed nucleotide sequence that acquire a pathological size, despite its polymorphic occurrence in normal individuals. To date, at least fourteen neurological disorders are associated with this phenomenon, including Huntington's disease (HD), dentatorubral and palidoluysian atrophy (DRPLA), spinobulbar and muscular atrophy (SBMA), myotonic dystrophy (DM), fragile X syndrome, FRAXE mental retardation and spinocerebellar ataxias (SCA) types 1-3, 6-8, 12 and 17. The spinocerebellar ataxias comprise a heterogeneous group of severe neurodegenerative-late onset disorders characterized by loss of balance and coordination. Most of the spinocerebellar ataxias exhibit an autosomal dominant pattern of inheritance and are promoted by the intergenerational expansion of a trinucleotide repeat (CAG)n inside the coding region of the respective gene. The expanded segment is translated into an abnormal polyglutamine tract in the protein, leading to the formation of nuclear aggregates that have been considered the basis of the pathogenesis in most of SCA types. One striking characteristic of these diseases is that the gene is expressed throughout the brain and also in other tissues but no pathological consequences are observed, despite the specific cellular degeneration. The characterization of the mutational event has led to the development of specific and sensitive molecular tests for direct DNA analysis, which allow confirmation of clinical diagnostic and an adequate therapeutic indication as well as genetic counseling.

The Structure of the AXH Domain of Spinocerebellar Ataxin-1

Spinocerebellar ataxia type 1 is a late-onset neurodegenerative disease caused by the expansion of a CAG triplet repeat in the SCA1 gene. This results in the lengthening of a polyglutamine tract in the gene product ataxin-1. This produces a toxic gain of function that results in specific neuronal death. A region in ataxin-1, the AXH domain, exhibits significant sequence similarity to the transcription factor HBP1. This region of the protein has been implicated in RNA binding and self-association. We have determined the crystal structure of the AXH domain of ataxin-1. The AXH domain is dimeric and contains an OB-fold, a structural motif found in many oligonucleotide-binding proteins, supporting its proposed role in RNA binding. By structure comparison with other proteins that contain an OB-fold, a putative RNA-binding site has been identified. We also identified a cluster of charged surface residues that are well conserved among AXH domains. These residues may constitute a second ligand-binding surface, suggesting that all AXH domains interact with a common yet unidentified partner.

Prominent Expression of Spinocerebellar Ataxia Type-1 (SCA1) Gene Encoding Ataxin-1 in LH-Producing Cells, L.BETA.T2

The LH-producing cell line, LbetaT2, and non LH-producing cell line, alphaT3-1 cells, established from a pituitary tumor, were employed for cDNA subtraction cloning to identify genes with expression unique to LH producing cells. Several cDNAs that code for known as well as for many unidentified clones were discovered. Most clones were the spinocerebellar ataxia type-1 (SCA1) gene encoding ataxin-1, the abnormality of which causes neurodegeneration and loss of cerebellar Purkinje cells. We examined whether the expression of SCA1 gene in LbetaT2 cells is related to hormone production. We also compared the expression of SCA1 with that in various other pituitary tumor derived cell lines, and confirmed the prominent expression of SCA1 in LbetaT2 cells. The effect of gonadal factor(s) for SCA1 gene expression was examined. The expression level in female rats was low and did not change during the estrus cycle, but increased significantly after ovariectomy and did not return to the normal level under low and high doses of estrogen. In the male pituitary SCA1 gene expression increased markedly after castration and was not decreased by estrogen or testosterone. The Ontogeny of SCA1 gene expression was investigated in porcine fetal and postnatal pituitaries and revealed biphasic and sexually dimorphic expression. Transient expression of SCA1 gene was observed at fetal day 50 and 65 in males and day 40 in females, followed by a decline and increased expression before birth in both genders. Thus the expression of SCA1 gene is prominent in LH-producing cells and is not under direct control of gonadal factor(s) in both genders. In addition to the variable expression of SCA1 gene during the fetus period, the present results provide a novel aspect to the understanding of Boucher-Neuhauser syndrome (Ataxia Hypogonadism Choroidal Dystrophy).

Stress responses of PML nuclear domains are ablated by ataxin-1 and other nucleoprotein inclusions

The polyglutamine diseases are characterized by expansion of triplet CAG repeats that encode polyglutamine tracts in otherwise unrelated proteins. One plausible explanation for the neurodegeneration of these disorders proposes that inclusions of such proteins sequester other significant nuclear proteins in inactive form. The present study shows that PML protein is sequestered by inclusions of the pathogenic mutant form of the polyglutamine protein ataxin-1 and that this sequestration removes from the nucleus the free 0.2-1 microm diameter PML nuclear domains (PML-NDs), together with at least one of their many cargo proteins (Sp100). The present study demonstrates that this sequestration can be effected equally by another nuclear protein, RED, which lacks a polyglutamine tract, but expresses a polar zipper repeat. The sequestered PML-NDs no longer respond to stress signals (heat shock or ionizing radiation) to which they are normally sensitive. In both cases, there is independent evidence that the cells initiate other responses to their injury (nuclear translocation of heat shock protein or generation of gamma-H2AX-rich nuclear foci, respectively). The data thus provide strong evidence that multiple species of nuclear inclusion functionally sequester PML-NDs. This mechanism is likely to distort cellular responses to injury of many different types.

Genetic polymorphism at spinocerebellar ataxia 1 and 2 loci in Brazil

Dynamic mutation involves the expansion of a tandem arrayed DNA sequence that is polymorphic in the population. This mechanism is associated with neurological/neuromuscular disorders and the pathology depends on the extension of the repeated tract, with a specific threshold for each disease. We made a PCR-based characterization of allelic polymorphism of SCA1 and SCA2 loci in a sample of 200 pairs of chromosomes in a population in Rio de Janeiro and found 23 different alleles at the SCA1 locus, varying from 10 to 39 CAG repeats (mean 27.7 +/- 3.3, mode 28) and 10 different alleles ranging from 19 to 29 CAG (mean 22.1 +/- 1.0, mode 22) at the SCA2 locus. The level of heterozygosis was 53% (SCA1) and 8% (SCA2).

Slipped (CTG).(CAG) repeats of the myotonic dystrophy locus: surface probing with anti-DNA antibodies

At least 15 human diseases have been associated with the length-dependent expansion of gene-specific (CTG).(CAG) repeats, including myotonic dystrophy (DM1) and spinocerebellar ataxia type 1 (SCA1). Repeat expansion is likely to involve unusual DNA structures. We have structurally characterized such DNA, with (CTG)(n).(CAG)(n) repeats of varying length (n=17-79), by high-resolution gel electrophoresis, and have probed their surfaces with anti-DNA antibodies of known specificities. We prepared homoduplex S-DNAs, which are (CTG)x.(CAG)y where x=y, and heteroduplex SI-DNAs, which are hybrids where x>y or x<y. S-DNAs formed many different species of slipped isomers, as indicated by its multiple electrophoretic species. In contrast, SI-DNAs formed distinct structures, as indicated by the limited electrophoretic species for all possible repeat length pairings. Sister SI-DNAs with an excess of CAG repeats always migrated slower than their sister SI-DNAs with an excess of CTG repeats. Strikingly, both the propensity to form slipped structures and the pattern of S-DNAs, but not SI-DNAs, varied for similar lengths of CTG/CAG repeats between the DM1 and SCA1 loci, highlighting a role for flanking cis-elements in S-DNA but not SI-DNA formation. Slipped structures bound structure and nucleotide-specific anti-DNA antibodies. Binding of anti-B-DNA antibodies was reduced for both S-DNAs and SI-DNAs relative to their linear forms. SI-DNAs bound anti-Z-DNA antibodies, while both S and SI-DNAs bound anti-cruciform antibodies, revealing shared characteristics between the corresponding DNA structures and slipped DNAs. Such features of the repeats may be recognized by cellular proteins known to bind such structures.

The AXH module: an independently folded domain common to ataxin-1 and HBP1

Ataxin-1 (ATX1), a human protein responsible for spinocerebellar ataxia type 1 in humans, shares a region of homology, named AXH module, with the apparently unrelated transcription factor HBP1. Here, we describe the first characterisation of the AXH module in terms of its structural properties and stability. By producing protein constructs spanning the AXH modules of ATX1 and HBP1 and by comparing their properties, we have identified the minimal region sufficient for forming independently folded units (domains). Knowledge of the AXH domain boundaries allows us to map many of the interactions of ATX1 with other molecules onto the AXH module. We further show that the AXH of ATX1 is a dimerisation domain and is able to recognise RNA with the same nucleotide preference previously described for the full-length protein. AXH is therefore a novel protein-protein and RNA binding motif.

Oxidative stimuli affect polyglutamine aggregation and cell death in human mutant ataxin-1-expressing cells

Spinocerebellar ataxia 1 (SCA1), one of the inherited polyglutamine neurodegenerative diseases, is associated with intracellular aggregates. However, the process of aggregate formation and the factors that influence aggregation remain unclear. Here, we show that oxidative stimuli and alteration of the cellular redox state significantly affect aggregation and cell death in cells expressing mutant ataxin-1, the SCA gene product. Treatment of cells with buthionine sulfoximine, hydrogen peroxide or t-butylhydroperoxide increased the formation of mutant ataxin-1 aggregates, but treatment with the anti-oxidant, N-acetylcysteine (NAC), decreased aggregate formation. Oxidative damage of mutant ataxin-1 protein increased its recruitment in nuclear aggregates and increased cell death. However, NAC treatments reduced cell death and the number of cells with abnormal morphology. Our results might give insight into the mechanism whereby polyglutamine proteins aggregate and suggest that treatment of appropriate antioxidant reagents might prevent progression of SCA1 and other polyglutamine diseases.

From fruit fly to bedside: translating lessons from Drosophila models of neurodegenerative disease

PURPOSE OF REVIEW

Fly models have been developed for a variety of neurodegenerative disorders, and the field is beginning to harness the power of Drosophila genetics to dissect pathways of disease pathogenesis and identify targets for therapeutic intervention. In this review, we emphasize the most recent accomplishments and chart the potential rewards in translating lessons from Drosophila models to clinical therapeutics.

RECENT FINDINGS

The conservation of human disease genes in the Drosophila genome forms the basis for several recent investigations of the normal biological functions of genes implicated in neurodegenerative disease. In addition, transgenic approaches continue to expand the list of diseases modeled in Drosophila that now includes Parkinson's disease, Alzheimer's disease, Huntington's disease, and several spinocerebellar ataxias. Studies based on these models suggest that protein folding and degradation pathways play an important role in Parkinson's disease and the polyglutamine repeat disorders, and that kinases and apoptotic pathways may modulate neurodegeneration in tauopathies.

SUMMARY

Ongoing genetic studies with Drosophila neurodegenerative disease models promise to enhance our understanding of disease pathogenesis and generate target lists for future investigational research and drug development. The next challenge will be distilling a growing number of possible targets into a shortlist for fast-track drug design and clinical trials. With the advent of neurodegenerative disease models, the fruit fly is rapidly assuming a unique niche in bench to bedside research.

Polyglutamine-expanded ataxin-1 recruits Cu/Zn-superoxide dismutase into the nucleus of HeLa cells

Spinocerebellar ataxia 1 (SCA1) is an inherited neurodegenerative disorder caused by expansion of the polyglutamine stretch in ataxin-1, the SCA1 gene product. Polyglutamine expansion leads to the aggregation of ataxin-1 proteins. Superoxide dismutases (SODs) are involved in the pathogenesis of other aggregate-forming neurodegenerative diseases and are known to localize in the cytoplasm. Here, we show that Cu/Zn-SOD is translocated into the nucleus of HeLa cells in the presence of expanded ataxin-1, whereas Mn-SOD is localized in the cytoplasm: the longer the expansion of polyglutamine, the higher the level of translocation of Cu/Zn-SOD. In addition, the oxidation of intracellular proteins occurs with higher frequency in the presence of mutant ataxin-1 (82Q), suggesting that the functional activity of Cu/Zn-SOD might be decreased by mutant ataxin-1. We demonstrate that mutant ataxin-1-expressing cells encounter mitochondrial dysfunction in the conditions of oxidative stress. Our results suggest that polyglutamine-expanded ataxin-1 increases the levels of reactive oxygen species in HeLa cells.

p80 coilin, a coiled body-specific protein, interacts with ataxin-1, the SCA1 gene product

Spinocerebellar ataxia type 1 (SCA1) is an autosomal-dominant neurodegenerative disorder characterized by ataxia and progressive motor deterioration. SCA1 is associated with an elongated polyglutamine tract in ataxin-1, the SCA1 gene product. Using the yeast two-hybrid system and co-immunoprecipitation experiments, we have found that p80 coilin, coiled body-specific protein, binds to ataxin-1. In further experiments with deletion mutants, we found that the C-terminal regions of ataxin-1 and p80 coilin were essential for this interaction. In HeLa cells that have been co-transfected with ataxin-1 and p80 coilin, the p80 coilin protein co-localizes with ataxin-1 aggregates in the nucleoplasm. However, immunohistochemical analysis and immunofluorescence assays showed that mutant ataxin-1 aggregates do not redistribute p80 coilin's dot-like structures in the Purkinje cells of SCA1 transgenic mice. This feature of the interaction between ataxin-1 and p80 coilin suggests that p80 coilin might be implicated in altering the function of ataxin-1.

Interaction of Akt-phosphorylated ataxin-1 with 14-3-3 mediates neurodegeneration in spinocerebellar ataxia type 1

Spinocerebellar ataxia type 1 (SCA1) is one of several neurological disorders caused by a CAG repeat expansion. In SCA1, this expansion produces an abnormally long polyglutamine tract in the protein ataxin-1. Mutant polyglutamine proteins accumulate in neurons, inducing neurodegeneration, but the mechanism underlying this accumulation has been unclear. We have discovered that the 14-3-3 protein, a multifunctional regulatory molecule, mediates the neurotoxicity of ataxin-1 by binding to and stabilizing ataxin-1, thereby slowing its normal degradation. The association of ataxin-1 with 14-3-3 is regulated by Akt phosphorylation, and in a Drosophila model of SCA1, both 14-3-3 and Akt modulate neurodegeneration. Our finding that phosphatidylinositol 3-kinase/Akt signaling and 14-3-3 cooperate to modulate the neurotoxicity of ataxin-1 provides insight into SCA1 pathogenesis and identifies potential targets for therapeutic intervention.

Serine 776 of ataxin-1 is critical for polyglutamine-induced disease in SCA1 transgenic mice

Polyglutamine-induced neurodegeneration in transgenic mice carrying the spinocerebellar ataxia type 1 (SCA1) gene is modulated by subcellular distribution of ataxin-1 and by components of the protein folding/degradation machinery. Since phosphorylation is a prominent mechanism by which these processes are regulated, we examined phosphorylation of ataxin-1 and found that serine 776 (S776) was phosphorylated. Residue 776 appeared to affect cellular deposition of ataxin-1[82Q] in that ataxin-1[82Q]-A776 failed to form nuclear inclusions in tissue culture cells. The importance of S776 for polyglutamine-induced pathogenesis was examined by generating ataxin-1[82Q]-A776 transgenic mice. These mice expressed ataxin-1[82Q]-A776 within Purkinje cell nuclei, yet the ability of ataxin-1[82Q]-A776 to induce disease was substantially reduced. These studies demonstrate that polyglutamine tract expansion and localization of ataxin-1 to the nucleus of Purkinje cells are not sufficient to induce disease. We suggest that S776 of ataxin-1 also has a critical role in SCA1 pathogenesis.

Role of histidine interruption in mitigating the pathological effects of long polyglutamine stretches in SCA1: A molecular approach

Polyglutamine expansions, leading to aggregation, have been implicated in various neurodegenerative disorders. The range of repeats observed in normal individuals in most of these diseases is 19-36, whereas mutant proteins carry 40-81 repeats. In one such disorder, spinocerebellar ataxia (SCA1), it has been reported that certain individuals with expanded polyglutamine repeats in the disease range (Q(12)HQHQ(12)HQHQ(14/15)) but with histidine interruptions were found to be phenotypically normal. To establish the role of histidine, a comparative study of conformational properties of model peptide sequences with (Q(12)HQHQ(12)HQHQ(12)) and without (Q(42)) interruptions is presented here. Q(12)HQHQ(12)HQHQ(12) displays greater solubility and lesser aggregation propensity compared to uninterrupted Q(42) as well as much shorter Q(22). The solvent and temperature-driven conformational transitions (beta structure <--> random coil --> alpha helix) displayed by these model polyQ stretches is also discussed in the present report. The study strengthens our earlier hypothesis of the importance of histidine interruptions in mitigating the pathogenicity of expanded polyglutamine tract at the SCA1 locus. The relatively lower propensity for aggregation observed in case of histidine interrupted stretches even in the disease range suggests that at a very low concentration, the protein aggregation in normal cells, is possibly not initiated at all or the disease onset is significantly delayed. Our present study also reveals that besides histidine interruption, proline interruption in polyglutamine stretches can lower their aggregation propensity.

Attenuated nuclear shrinkage in neurones with nuclear inclusions of SCA1 brains

BACKGROUND

Spinocerebellar ataxia type 1 (SCA1) is one of the autosomal dominant neurodegenerative disorders commonly linked to pathological expansion of the CAG repeat of the relevant gene. Nuclear inclusions and neurodegeneration are both triggered by this pathological expansion of the CAG/polyglutamine repeat on ataxin-1, but it remains to be determined whether or not nuclear inclusion formation is associated with accelerated neurodegeneration.

OBJECTIVE

To examine the influence of nuclear inclusions on nuclear size and deformity in human brains from patients suffering from SCA1.

MATERIAL

Pontine sections of brains obtained at necropsy from seven patients with SCA1 and five controls.

METHODS

The size and deformity of each neuronal nucleus was quantified. Nuclei with and without inclusions were examined separately to assess the possible influence of nuclear inclusions on neurodegeneration.

RESULTS

Nuclear shrinkage and deformity were more marked in SCA1 brains than in controls. This shrinkage was attenuated in neurones containing nuclear inclusions.

CONCLUSIONS

The existence of nuclear inclusions in SCA1 is presumably linked to a mechanism that attenuates rather than accelerates nuclear shrinkage. This in vivo finding may provide a clue to constructing a rational therapeutic strategy for combating neurodegeneration associated with nuclear inclusions.

Temporal patterns of bone marrow cell differentiation following transplantation in doxorubicin-induced cardiomyopathy

OBJECTIVE

Recent studies have suggested benefits of bone marrow cell transplantation for the regeneration of ischemic cardiac tissue. To extend the potential of cell transplantation, we assessed this treatment in a mouse model of acute nonischemic doxorubicin-induced cardiomyopathy.

METHODS

To allow detection of engrafted cells, we used transgenic mice expressing the nuclear-located LacZ under the control of either desmin or vimentin promoters, which identify muscle lineage and mesenchymal cells, respectively. All transplanted cells were also labeled with the fluorescent dye DIL. One week after the administration of doxorubicin (15 mg/kg), mice were intramyocardially injected with either allogeneic unpurified bone marrow cells (6 x 10(6) in 30 microl, n=59) or purified sca-1(pos) cells (4 x 10(5) in 30 microl, n=22). In parallel, control normal mice received only unpurified bone marrow cells (n=28). Hearts were harvested at serial intervals until 2 weeks after transplantation and analyzed by immunohistochemistry to assess the degree of engraftment and transplanted cell differentiation.

RESULTS

In control mice, no differentiation of bone marrow cells was detected. In contrast, unpurified bone marrow cells grafted into diseased myocardium featured two successive phases of cell differentiation. The first yielded cells with a mesenchymal phenotype (44.1+/-10.1 cells/3 x 10(-2) mm(3) at 2 days), was transient and lasted 1 week. The second phase was characterized by cells with a muscular phenotype detected in a small number of cells (5.6+/-2.3 cells/3 x 10(-2) mm(3) at 7 days). Two weeks after transplantation, some of these cells appeared phenotypically close to cardiomyocytes, as evidenced by morphology and positive staining for myosin binding protein C, vinculin and myosin heavy chain. In sca-1(pos) hematopoietic progenitor grafted mice hearts, no transdifferentiation into cardiac cells was detected at any time point.

CONCLUSION

These data support the hypothesis of the potential for a myogenic differentiation of bone marrow cells following engraftment in a nonischemic model of global cardiomyopathy. Bone marrow-derived cells amenable to cardiac differentiation are present in total unpurified bone marrow but not in the sca-1(pos) hematopoietic progenitor cell population. However, the very small number of transdifferentiated cells raises concerns over their functional efficacy.

PQBP-1 transgenic mice show a late-onset motor neuron disease-like phenotype

A body of experimental evidence indicates that transcription and/or mRNA processing factors interacting with the polyglutamine disease gene products play crucial roles in the pathology. PQBP-1 is one of these factors and it has been shown to interact with the spinocerebellar ataxia type-1 (SCA1) disease gene product, ataxin-1. Our previous data suggested that relatively high expression of PQBP-1 in the cerebellum might explain the selective neuronal degeneration of SCA1. To further test whether PQBP-1 expression level regulates neuronal death, we generated transgenic mice of human PQBP-1 driven by a regulatory element for ubiquitous gene expression. The mice showed a late-onset and gradually progressive motor neuron disease-like phenotype, which might be related to neurogenic muscular atrophy observed in SCA1 patients. Ataxia could not be discriminated from predominant progressive weakness. Pathological examinations of the transgenic mice revealed loss of Purkinje and granular cells in the cerebellum as well as that of spinal motor neurons, corresponding to the pathology of human SCA1. These findings show that excessive action of PQBP-1 causes neuronal dysfunction and support PQBP-1 being involved in the pathology of SCA1.

[Analysis of the allele polymorphism of (CTG)n and (GAG)n triplet repeats in DM, DRPLA, and SCA1 genes in various populations of Russia]

Polymorphism of highly polymorphic triplet repeats CTG of the 3'-untranslated region of the myotonin protein kinase gene and CAG of the genes associated with dentatorobral-pallidoluysian atrophy (DRPLA, or Hew River syndrome) and spinocerebellar ataxia type 1 (SCA1) was analyzed in several ethnic populations of Russia. A difference in allele spectra of the three genes was demonstrated for populations differing in ethnic origin.

Aggregate formation inhibits proteasomal degradation of polyglutamine proteins

Insoluble protein aggregates are consistently found in neurodegenerative disorders caused by expanded polyglutamine [poly(Q)] repeats. The aggregates contain various components of the ubiquitin/proteasome system, suggesting an attempt of the cell to clear the aberrant substrate. To investigate the effect of expanded poly(Q) repeats on ubiquitin/proteasome-dependent proteolysis, we targeted these proteins for proteasomal degradation by the introduction of an N-end rule degradation signal. While soluble poly(Q) proteins were degraded, they resisted proteasomal degradation once present in the aggregates. Stabilization was also observed for proteins that are co-aggregated via interaction with the expanded poly(Q) domain. Introduction of a degradation signal in ataxin-1/Q92 reduced the incidence of nuclear inclusions and the cellular toxicity, conceivably by accelerating the clearance of the soluble substrate.