Nucleic Acids Research Advance Access published online on September 27, 2008
Nucleic Acids Research, doi:10.1093/nar/gkn604
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Gene regulation, Chromatin and Epigenetics |
Long intronic GAA•TTC repeats induce epigenetic changes and reporter gene silencing in a molecular model of Friedreich ataxia
1Center for Genome Research, Institute of Biosciences and Technology, Texas A&M Health Science Center, 2121 West Holcombe Blvd., Houston, TX, 77030, 2The Scripps Research Institute, Department of Molecular Biology, 10550 North Torrey Pines Road, La Jolla, CA, 92037 and 3University of Texas M. D. Anderson Cancer Center, Department of Biochemistry and Molecular Biology and Center for Cancer Epigenetics, 1515 Holcombe Blvd., Houston, TX, 77030, USA
*To whom correspondence should be addressed. Tel: +1 (713) 745 1892; Fax: 713 834 6273; Email: mnapiera{at}mdanderson.org
Received August 1, 2008. Revised September 5, 2008. Accepted September 5, 2008.
Friedreich ataxia (FRDA) is caused by hyperexpansion of GAA•TTC repeats located in the first intron of the FXN gene, which inhibits transcription leading to the deficiency of frataxin. The FXN gene is an excellent target for therapeutic intervention since (i) 98% of patients carry the same type of mutation, (ii) the mutation is intronic, thus leaving the FXN coding sequence unaffected and (iii) heterozygous GAA•TTC expansion carriers with 
50% decrease of the frataxin are asymptomatic. The discovery of therapeutic strategies for FRDA is hampered by a lack of appropriate molecular models of the disease. Herein, we present the development of a new cell line as a molecular model of FRDA by inserting 560 GAA•TTC repeats into an intron of a GFP reporter minigene. The GFP_(GAA•TTC)560 minigene recapitulates the molecular hallmarks of the mutated FXN gene, i.e. inhibition of transcription of the reporter gene, decreased levels of the reporter protein and hypoacetylation and hypermethylation of histones in the vicinity of the repeats. Additionally, selected histone deacetylase inhibitors, known to stimulate the FXN gene expression, increase the expression of the GFP_(GAA•TTC)560 reporter. This FRDA model can be adapted to high-throughput analyses in a search for new therapeutics for the disease.