Background: The Repeat Expansion Diseases are caused by the intergenerational expansion of a specific tandem repeat. Expansion of a CGG?CCG-repeat in the 5' UTR of the FMR1 gene is associated with 3 different clinical presentations: Individuals with 60-200 repeats, the so-called premutation allele, are at risk for Fragile X-associated tremor-ataxia syndrome whose symptoms include dementia as well as bowel and urinary incontinence. Female carriers of premutation alleles are also at risk of premature ovarian failure. Furthermore, in females, the premutation allele can undergo expansion on intergenerational transfer that can result in their children having alleles with >200 repeats. This expanded allele is known as a full mutation and individuals who inherit such alleles almost always have Fragile X mental retardation syndrome (FXS). FXS is the most common cause of mental retardation and the most common known cause of autism. Hyperphagia and obesity are common comorbid features. FXS symptoms result from some combination of repeat-induced gene silencing and difficulties in translating any residual FMR1 mRNA. This results in a deficiency of the protein product of this gene, FMRP, a protein involved in the regulation of translation of certain mRNAs. GAA?TTC-repeat expansion in the first intron of the frataxin gene causes a deficit in mRNA for Frataxin a protein involved in iron homeostasis in the mitochondria. This deficit produces Friedreich ataxia (FRDA), a progressive degenerative disease associated with cerebellar dysfunction, hypertrophic cardiomyopathy, and diabetes. We are interested in both the mechanism of expansion and the consequences of expansion in these disorders.? ? Progress report: We had previously generated FXS premutation mice containing 120 CGG?CCG-repeats in the 5? UTR of the endogenous murine Fmr1 gene. Like humans with the same number of repeats, these mice produce elevated levels of Fmr1 mRNA that recent data, from my group and elsewhere, suggests is toxic. Microarray analysis shows a number of interesting changes in gene expression in the brains and ovaries that are consistent with some of the pathological changes that we can see in these mice. These pathological changes include the accumulation of ubiquitin and lamin A/C positive intranuclear neuronal inclusions in brain that are reminiscent of those seen in human carriers of premutation alleles. We have also identified a CGG-RNA binding protein in brain that may be associated with the RNA toxicity. We have also shown that mice with premutation alleles have a discernable decrease in the Fmr1 gene product, FMRP, in particular parts of the brain. This finding has consequences for some of the symptoms seen in premutation carriers. We have also shown that the GAA?TTC-repeat expansion responsible for FRDA has epigenetic effects resulting in the accumulation of histone modifications characteristic of transcriptionally silenced genes. Similar chromatin modifications are found at the FMR1 promoter in FXS. This raises the possibility that disease pathology in FXS and FRDA have a similar underlying mechanism. We are currently in the process of studying the molecular triggers for this gene silencing in cell lines from patients with FXS and FRDA as well as in a mice model we have generated for FXS. We have also identified a number of small molecules capable of affecting gene expression in FXS. This is important in that it throws light on the mechanism of gene silencing and also suggests potential approaches to reversing or ameliorating disease symptoms.

Agency
National Institute of Health (NIH)
Institute
National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK)
Type
Intramural Research (Z01)
Project #
1Z01DK057602-10
Application #
7337503
Study Section
(LMCB)
Project Start
Project End
Budget Start
Budget End
Support Year
10
Fiscal Year
2006
Total Cost
Indirect Cost
Name
U.S. National Inst Diabetes/Digst/Kidney
Department
Type
DUNS #
City
State
Country
United States
Zip Code
Kumari, Daman; Usdin, Karen (2009) Chromatin remodeling in the noncoding repeat expansion diseases. J Biol Chem 284:7413-7
Entezam, Ali; Biacsi, Rea; Orrison, Bonnie et al. (2007) Regional FMRP deficits and large repeat expansions into the full mutation range in a new Fragile X premutation mouse model. Gene 395:125-34
Mahishi, Lata; Usdin, Karen (2006) NF-Y, AP2, Nrf1 and Sp1 regulate the fragile X-related gene 2 (FXR2). Biochem J 400:327-35
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Greene, Eriko; Entezam, Ali; Kumari, Daman et al. (2005) Ancient repeated DNA elements and the regulation of the human frataxin promoter. Genomics 85:221-30
Handa, Vaishali; Goldwater, Deena; Stiles, David et al. (2005) Long CGG-repeat tracts are toxic to human cells: implications for carriers of Fragile X premutation alleles. FEBS Lett 579:2702-8
Kumari, Daman; Gabrielian, Andrei; Wheeler, David et al. (2005) The roles of Sp1, Sp3, USF1/USF2 and NRF-1 in the regulation and three-dimensional structure of the Fragile X mental retardation gene promoter. Biochem J 386:297-303
Greene, E; Handa, V; Kumari, D et al. (2003) Transcription defects induced by repeat expansion: fragile X syndrome, FRAXE mental retardation, progressive myoclonus epilepsy type 1, and Friedreich ataxia. Cytogenet Genome Res 100:65-76
Handa, Vaishali; Saha, Tapas; Usdin, Karen (2003) The fragile X syndrome repeats form RNA hairpins that do not activate the interferon-inducible protein kinase, PKR, but are cut by Dicer. Nucleic Acids Res 31:6243-8
Fleming, K; Riser, D K; Kumari, D et al. (2003) Instability of the fragile X syndrome repeat in mice: the effect of age, diet and mutations in genes that affect DNA replication, recombination and repair proficiency. Cytogenet Genome Res 100:140-6

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