Friedreich ataxia is the most common inherited ataxia. Friedreich ataxia patients have large expansions of a GAA triplet-repeat sequence in both copies of the FXN gene. The progressive ataxia is mainly "sensory" and is due to primary degeneration of dorsal root ganglia (DRG). The cause for the selective and progressive degeneration of the sensory DRG neurons is not known. A sensitive method called small pool PCR to analyze somatic instability of the expanded GAA triplet-repeat sequence revealed that patients have further large expansions in their DRG, which accumulated in an age-dependent fashion. Moreover, in a "humanized" transgenic mouse model carrying an expanded GAA triplet-repeat sequence within the context of the entire human FXN gene, the same age-dependent increase in prevalence of large expansions in the DRG was observed. The goal of this project is to evaluate the role of this somatic instability in Friedreich ataxia. We hypothesize that these large expansions occur specifically in neurons, and based on preliminary data, that the underlying mechanism involves DNA double-strand breaks (DSBs). We will use single-cell analysis of neurons and glial cells from DRG of two humanized transgenic mouse models to investigate what cell-type is responsible for the large expansions observed in whole-tissue preparations. DRG neurons obtained from autopsy tissue of multiple Friedreich ataxia patients will be similarly analyzed. To test the hypothesis that DSBs are associated with tissue-specific somatic instability, co-localization studies with immunofluorescence and FISH, and chromatin immunoprecipitation experiments will be used to identify DSBs at the site of the expanded GAA triplet- repeat sequence in vivo. The effect of DSBs on GAA repeat instability will be directly tested in cell culture experiments by either using repair-deficient cell lines, or treating cells from patients with DSB-inducing drugs. Finally, to test the hypothesis that the expanded GAA triplet-repeat is inordinately susceptible to DSBs, we will cross the existing mouse models for somatic instability on to a repair-deficient, ATM null background. Our data will have important implications for understanding the pathogenesis of Friedreich ataxia. Additionally, if a mechanism for the somatic instability is identified, this may yield new clues for the development of a specific therapy to slow disease progression.
Patients with Friedreich ataxia, the most common inherited ataxia, have expanded GAA repeat sequences in their FXN genes. Preliminary results indicate that instability of this sequence is important for the pathogenesis and progression of disease. Our experiments are designed to confirm this notion, and to determine the mechanism of this DNA instability.
|Ezzatizadeh, Vahid; Pinto, Ricardo Mouro; Sandi, Chiranjeevi et al. (2012) The mismatch repair system protects against intergenerational GAA repeat instability in a Friedreich ataxia mouse model. Neurobiol Dis 46:165-71|
|Bourn, Rebecka L; De Biase, Irene; Pinto, Ricardo Mouro et al. (2012) Pms2 suppresses large expansions of the (GAAÂ·TTC)n sequence in neuronal tissues. PLoS One 7:e47085|
|Rindler, Paul M; Bidichandani, Sanjay I (2011) Role of transcript and interplay between transcription and replication in triplet-repeat instability in mammalian cells. Nucleic Acids Res 39:526-35|
|Bourn, Rebecka L; Rindler, Paul M; Pollard, Laura M et al. (2009) E. coli mismatch repair acts downstream of replication fork stalling to stabilize the expanded (GAA.TTC)(n) sequence. Mutat Res 661:71-7|
|Rasmussen, Astrid; De Biase, Irene; Fragoso-Benitez, Marcela et al. (2007) Anticipation and intergenerational repeat instability in spinocerebellar ataxia type 17. Ann Neurol 61:607-10|
|Alonso, Elisa; Martinez-Ruano, Leticia; De Biase, Irene et al. (2007) Distinct distribution of autosomal dominant spinocerebellar ataxia in the Mexican population. Mov Disord 22:1050-3|
|De Biase, Irene; Rasmussen, Astrid; Endres, Dan et al. (2007) Progressive GAA expansions in dorsal root ganglia of Friedreich's ataxia patients. Ann Neurol 61:55-60|
|Rasmussen, A; Gomez, M; Alonso, E et al. (2006) Clinical heterogeneity of recessive ataxia in the Mexican population. J Neurol Neurosurg Psychiatry 77:1370-2|
|Clark, Rhonda M; Bhaskar, Sanjeev S; Miyahara, Masaki et al. (2006) Expansion of GAA trinucleotide repeats in mammals. Genomics 87:57-67|
|Gomez, Mariluz; Clark, Rhonda M; Nath, Swapan K et al. (2004) Genetic admixture of European FRDA genes is the cause of Friedreich ataxia in the Mexican population. Genomics 84:779-84|
Showing the most recent 10 out of 13 publications