Mouse tissue culture models of unstable triplet repeats.
ABSTRACT Once into the expanded disease-associated range, trinucleotide repeat alleles become dramatically unstable in the germline and in somatic cells. The molecular mechanism(s) that underlie this unique form of dynamic mutation are poorly understood. Numerous transgenic mouse models of unstable trinucleotide repeats, which reconstitute the dynamic nature of somatic mosaicism observed in humans, have been generated. Given their easy accessibility, tissues from these mice can be collected to establish homogenous cell culture models of trinucleotide repeat dynamics. This chapter describes how such cultures can be established and maintained. Such in vitro systems may be useful to study relevant biological questions concerning fundamental triplet repeat metabolism. In particular, monitoring of repeat stability in cells growing under controlled conditions could help to clarify the relationship among the accumulation of repeat length variation, cell division rates, and DNA replication.
Chapter: Mechanisms of DNA Repeat Expansion12/2005: pages 3-53;
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ABSTRACT: A mounting number of inherited human disorders, including Huntington disease, myotonic dystrophy, fragile X syndrome, Friedreich ataxia and several spinocerebellar ataxias, have been associated with the expansion of unstable simple sequence DNA repeats. Despite a similar genetic basis, pathogenesis in these disorders is mediated by a variety of both loss and gain of function pathways. Thus, therapies targeted at downstream pathology are likely to be disease specific. Characteristically, disease-associated expanded alleles in these disorders are highly unstable in the germline and somatic cells, with a tendency towards further expansion. Whereas germline expansion accounts for the phenomenon of anticipation, tissue-specific, age-dependent somatic expansion may contribute towards the tissue-specificity and progressive nature of the symptoms. Thus, somatic expansion presents as a novel therapeutic target in these disorders. Suppression of somatic expansion should be therapeutically beneficial, whilst reductions in repeat length could be curative. It is well established that both cis- and trans-acting genetic modifiers play key roles in the control of repeat dynamics. Importantly, recent data have revealed that expanded CAG.CTG repeats are also sensitive to a variety of trans-acting chemical modifiers. These data provide an exciting proof of principle that drug induced suppression of somatic expansion might indeed be feasible. Moreover, as our understanding of the mechanism of expansion is refined more rational approaches to chemical intervention in the expansion pathway can be envisioned. For instance, the demonstration that expansion of CAG.CTG repeats is dependent on the Msh2, Msh3 and Pms2 genes, highlights components of the DNA mismatch repair pathway as therapeutic targets. In addition to potential therapeutic applications, the response of expanded simple repeats to genotoxic assault suggests such sequences could also have utility as bio-monitors of environmentally induced genetic damage in the soma.Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis 07/2006; 598(1-2):15-34. DOI:10.1016/j.mrfmmm.2006.01.011 · 4.44 Impact Factor
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ABSTRACT: This chapter discusses mechanisms and consequences of somatic mosaicism of expanded CAG·CTG repeats in humans and mice. Age dependent, tissue-specific, expansion-biased somatic mosaicism is a major feature of the CAG·CTG repeat disorders. The diseases associated with CAG·CTG repeat expansions include the neurodegenerative disorders in which a CAG repeat encodes a polyglutamine tract in the resultant protein: spinal and bulbar muscular atrophy (SBMA), Huntington disease (HD), dentatorubral pallidoluysian atrophy (DRPLA), Machado–Joseph disease (MJD), and the other spinocerebellar ataxias, types 1, 2, 7, and 17. There are two principal approaches to genotyping and measuring the degree of somatic mosaicism in CAG·CTG repeat disorders. First, traditional Southern blot hybridization of restriction-enzyme-digested genomic DNA; and second, methodologies based upon polymerase chain reaction (PCR) analysis. The role of somatic mosaicism in exacerbating the tissue specificity and progressive nature of the symptoms suggests that suppression of the rate of somatic expansion is also likely to be therapeutically beneficial. Moreover, in all disorders, even those in which somatic mosaicism may not be critical, reversion of the repeat tract to a length that falls below the disease threshold would be predicted to be curative.Genetic Instabilities and Neurological Diseases, 12/2006: pages 537-561; , ISBN: 9780123694621