Galen Breningstall

Bio: Galen Breningstall is an academic researcher. The author has contributed to research in topics: Oligomer restriction & Trinucleotide repeat expansion. The author has an hindex of 1, co-authored 1 publications receiving 69 citations.

Childhood‐onset ataxia: Testing for large CAG‐repeats in SCA2 and SCA7

Abstract: Infantile- and juvenile-onset spinal cerebellar ataxia (SCA) is associated with expansion of 130 to more than 200 CAG-repeats in the SCA2 and SCA7 genes. Routine clinical assays for SCA2 and SCA7, which use polymerase chain reaction (PCR) and denaturing PAGE (polyacrylamide gel electrophoresis), will not reliably detect such large expansions. An assay based on separation of PCR products on an agarose gel, blotting, and hybridization with a (CAG)6 oligonucleotide probe was used to test DNA from individuals more than 10 years of age who had a possible diagnosis of SCA. Among 25 cases, the PCR-blot assay confirmed the presence of SCA2 expansions between 230 and 500 repeats in four unrelated individuals, but did not detect any cases of extreme expansion in the SCA7 gene. The PCR-blot assay provides reliable detection of extreme expansion mutations. Routine incorporation of this assay in clinical laboratories may reveal that infantile-juvenile forms of SCA2 and SCA7 are more prevalent than previously recognized.

Microsatellites Within Genes: Structure, Function, and Evolution

Abstract: Recently, increasingly more microsatellites, or simple sequence repeats (SSRs) have been found and characterized within protein-coding genes and their untranslated regions (UTRs). These data provide useful information to study possible SSR functions. Here, we review SSR distributions within expressed sequence tags (ESTs) and genes including protein-coding, 3'-UTRs and 5'-UTRs, and introns; and discuss the consequences of SSR repeat-number changes in those regions of both prokaryotes and eukaryotes. Strong evidence shows that SSRs are nonrandomly distributed across protein-coding regions, UTRs, and introns. Substantial data indicates that SSR expansions and/or contractions in protein-coding regions can lead to a gain or loss of gene function via frameshift mutation or expanded toxic mRNA. SSR variations in 5'-UTRs could regulate gene expression by affecting transcription and translation. The SSR expansions in the 3'-UTRs cause transcription slippage and produce expanded mRNA, which can be accumulated as nuclear foci, and which can disrupt splicing and, possibly, disrupt other cellular function. Intronic SSRs can affect gene transcription, mRNA splicing, or export to cytoplasm. Triplet SSRs located in the UTRs or intron can also induce heterochromatin-mediated-like gene silencing. All these effects caused by SSR expansions or contractions within genes can eventually lead to phenotypic changes. SSRs within genes evolve through mutational processes similar to those for SSRs located in other genomic regions including replication slippage, point mutation, and recombination. These mutational processes generate DNA changes that should be connected by DNA mismatch repair (MMR) system. Mutation that has escaped from the MMR system correction would become new alleles at the SSR loci, and then regulate and/or change gene products, and eventually lead to phenotype changes. Therefore, SSRs within genes should be subjected to stronger selective pressure than other genomic regions because of their functional importance. These SSRs may provide a molecular basis for fast adaptation to environmental changes in both prokaryotes and eukaryotes.

SHORT REVIEW EST-SSRs as a resource for population genetic analyses

Abstract: Simple-sequence repeats (SSRs) have increasingly become the marker of choice for population genetic analyses. Unfortunately, the development of traditional ‘anonymous’ SSRs from genomic DNA is costly and time-consuming. These problems are further compounded by a paucity of resources in taxa that lack clear economic importance. However, the advent of the genomics age has resulted in the production of vast amounts of publicly available DNA sequence data, including large collections of expressed sequence tags (ESTs) from a variety of different taxa. Recent research has revealed that ESTs are a potentially rich source of SSRs that reveal polymorphisms not only within the source taxon, but in related taxa, as well. In this paper, we review what is known about the transferability of EST-SSRs from one taxon to another with particular reference to the potential of these markers to facilitate population genetic studies. As an example of the utility of these resources, we then cross-reference existing EST databases against lists of rare, endangered and invasive plant species and conclude that half of all suitable EST databases could be exploited for the population genetic analysis of species of conservation concern. We then discuss the advantages and disadvantages of EST-SSRs in the context of population genetic applications.

EST-SSRs as a resource for population genetic analyses.

Abstract: Simple-sequence repeats (SSRs) have increasingly become the marker of choice for population genetic analyses. Unfortunately, the development of traditional 'anonymous' SSRs from genomic DNA is costly and time-consuming. These problems are further compounded by a paucity of resources in taxa that lack clear economic importance. However, the advent of the genomics age has resulted in the production of vast amounts of publicly available DNA sequence data, including large collections of expressed sequence tags (ESTs) from a variety of different taxa. Recent research has revealed that ESTs are a potentially rich source of SSRs that reveal polymorphisms not only within the source taxon, but in related taxa, as well. In this paper, we review what is known about the transferability of EST-SSRs from one taxon to another with particular reference to the potential of these markers to facilitate population genetic studies. As an example of the utility of these resources, we then cross-reference existing EST databases against lists of rare, endangered and invasive plant species and conclude that half of all suitable EST databases could be exploited for the population genetic analysis of species of conservation concern. We then discuss the advantages and disadvantages of EST-SSRs in the context of population genetic applications.

Spinocerebellar ataxia 2 (SCA2).

Abstract: Spinocerebellar ataxia type 2 (SCA2) is an autosomal dominantly inherited, neurodegenerative disease. It can manifest either with a cerebellar syndrome or as Parkinson's syndrome, while later stages involve mainly brainstem, spinal cord and thalamus. This particular atrophy pattern resembles sporadic multi-system-atrophy (MSA) and results in some clinical features indicative of SCA2, such as early saccade slowing, early hyporeflexia, severe tremor of postural or action type, and early myoclonus. For treatment, levodopa is temporarily useful for rigidity/bradykinesia and for tremor, magnesium for muscle cramps, but neuroprotective therapy will depend on the elucidation of pathogenesis. The disease cause lies in the polyglutamine domain of the protein ataxin-2, which can expand in families over successive generations resulting in earlier onset age and faster progression. Genetic testing in SCA2 and other polyglutamine disorders like the well-studied Huntington's disease is now readily available for family planning. Although these disorders differ clinically and in the affected neuron populations, it is not understood how the different polyglutamine proteins mediate such tissue specificity. The neuronal intranuclear inclusion bodies described in other polyglutamine disorders are not frequent in SCA2. For the quite ubiquitously expressed ataxin-2, a subcellular localization at the Golgi, the endoplasmic reticulum and the plasma membrane, in interaction with proteins of mRNA translation and of endocytosis have been observed. As a first victim of SCA2 degeneration, cerebellar Purkinje neurons may be preferentially susceptible to alterations of these subcellular pathways, and therefore our review aims to portray the particular profile of the SCA2 disease process and correlate it to the specific features of ataxin-2.

The pathogenic mechanisms of polyglutamine diseases and current therapeutic strategies

Abstract: Expansion of CAG trinucleotide repeat within the coding region of several genes results in the production of proteins with expanded polyglutamine (PolyQ) stretch. The expression of these pathogenic proteins leads to PolyQ diseases, such as Huntington's disease or several types of spinocerebellar ataxias. This family of neurodegenerative disorders is characterized by constant progression of the symptoms and molecularly, by the accumulation of mutant proteins inside neurons causing their dysfunction and eventually death. So far, no effective therapy actually preventing the physical and/or mental decline has been developed. Experimental therapeutic strategies either target the levels or processing of mutant proteins in an attempt to prevent cellular deterioration, or they are aimed at the downstream pathologic effects to reverse or ameliorate the caused damages. Certain pathomechanistic aspects of PolyQ disorders are discussed here. Relevance of disease models and recent knowledge of therapeutic possibilities is reviewed and updated.