Human BAC-mediated rescue of the Friedreich ataxia knockout mutation in transgenic mice
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Three independent transgenic mouse lines were generated with the human Friedreich ataxia gene, FRDA, in an 188-kb bacterial artificial chromosome (BAC) genomic sequence. Three copies of the transgene per diploid mouse genome were integrated in a single site in each mouse line. Transgenic mice were mated with mice heterozygous for a knockout mutation of the murine Frda gene, to generate mice homozygous for the Frda knockout mutation and hemizygous or homozygous for the human transgene. Rescue of the embryonic lethality that is associated with homozygosity for the Frda knockout mutation was observed in all three lines. Rescued mice displayed normal behavioral and biochemical parameters. RT-PCR analysis demonstrated that human FRDA mRNA is expressed in all the lines. The relative expression of the human FRDA and mouse Frda genes showed a similar pattern in different tissues in all three lines, indicating position-independent control of expression of the human FRDA transgene. However, large differences in the human:mouse mRNA ratio were observed between different tissues in all three lines. The human transgene is expressed at much higher levels in the brain, liver, and skeletal muscle than the endogenous gene, while expression of the human transgene in blood is only 25–30% of the mouse gene. These studies will facilitate the development of humanized mouse models of Friedreich ataxia through introduction of a GAA trinucleotide expansion or specific known point mutations in the normal human FRDA locus and the study of the regulation of gene expression from the FRDA locus.
KeywordsBacterial Artificial Chromosome Bacterial Artificial Chromosome Clone Denature High Performance Liquid Chromatography Friedreich Ataxia Founder Mouse
We thank J. Vadolas and D. Jamsai for advice on microinjection procedures and J. Scott for performing the microinjections. We thank A. Sylvain, C. Turner, J. Broughton, N. Kerr, and S. de la Rue for animal care; A. Gibbs and E. Tamanas for technical assistance; and M. Pook for informative discussions. All animal procedures were conducted under the approval of the Royal Children’s Hospital Animal Experimentation Ethics Committee. This study was supported by grants from the Muscular Dystrophy Association (USA), the ‘Seek a Miracle ’ Fund, the Friedreich Ataxia Research Alliance, the Ronald Geoffrey Arnott Foundation, and by a block grant from the National Health and Medical Research Council of Australia. We also acknowledge the Victorian and New South Wales FA support groups for their moral and financial support.
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