STOCK Fxn^tm1Mkn Tg(FXN)YG22Pook/J

Stock number: 010963
Product name: Frda^-; YG22
Strain synonyms: YG22R
Research areas: Mouse/Human Gene Homologs, Neurobiology Research, Sensorineural Research

Description

Mice that are homozygous for the Fxn^tm1Mkn (frataxin) targeted allele and hemizygous for the Tg(FXN)YG22Pook (frataxin, human) transgene, display an age dependent, tissue specific expansion of the GAA repeat, with expansion accumulation in the CNS (particularly cerebellum), similar to the human pathology of Friedreich's Ataxia. They also exhibit progressive retinal degeneration, impaired and decreased locomotor activity and coordination, an increase in body weight, and neurodegeneration.

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Detailed description

The YG22 transgenic founder line carries a single copy of the human FXN gene with one GAA trinucleotide repeat sequence of 190 repeats. High levels of human FXN gene product (mRNA or protein) are detected by RT-PCR and Western blot analysis. 40-50% of the endogenous mouse Fxn gene product (protein) is detected by Western blot analysis in mice heterozygous for the targeted mutation alone. Mice that are homozygous for the targeted allele and hemizygous for the transgene exhibit an age dependent, tissue specific expansion of the GAA repeat, with expansion accumulation in the CNS (particularly cerebellum), similar to the human pathology. The GAA triplet repeat exhibits intergenerational instability. Mice that are homozygous for the targeted allele and hemizygous for the transgene exhibit progressive retinal degeneration, impaired and decreased locomotor activity and coordination, and an increase in body weight. At 9 months of age, muscle strength is decreased. Although, histological analysis reveals progressive vacuolation of the dorsal root ganglia, no abnormalities or loss of cerebellar Purkinje cells were detected. Iron deposition in cardiac tissue of 14-18 month old mice is observed. Dorsal root ganglia neurons contain lipofuscin deposits, and large axons are swollen and exhibit secondary demyelination. Cardiomyocytes contain lipofuscin deposits, free glycogen accumulation and disrupted mitochondria. Mitochondrial respiratory chain function is decreased and oxidized protein levels are increased. This mutant mouse strain may be useful in studies of Friedreich's Ataxia.

Importation of this model was supported by the Friedreich's Ataxia Research Alliance (FARA) .

Development

These double mutant mice, heterozygous for the targeted mutation and hemizygous for the transgene, were generated by crossing transgenic mice (founder line YG22) with Fxn^tm1Mkn targeted mutant mice.

Drs. Michel Koenig and Helene Puccio generated the Fxn targeted mutation allele by disrupting exon 4 and flanking sequences with a loxP site flanked PGK-neo cassette. The construct was electroporated into 129/Sv derived embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6J blastocysts. The resulting chimeric animals were crossed to C57BL/6J mice, and then backcrossed to C57BL/6J for 5 generations. The mice carry the floxed selection cassette.

The transgenic construct consisting of a 370kb YAC insert that includes the entire human FXN gene with GAA triplet repeat sequences, was injected into fertilized CBA X C57BL/6 hybrid fertilized oocytes. Founder line YG22 was established, carrying a single copy of the human FXN gene with one GAA trinucleotide repeat sequence of 190 repeats. Founder animals were bred to wildtype C57BL/6J mice.

The two lines were then crossed to generate the double mutant. The Donating Investigator breeds mice that are heterozygous for the Fxn^tm1Mkn targeted mutation and hemizygous for the YG22 transgene to mice that are heterozygous for the Fxn^tm1Mkn targeted mutation to obtain mice homozygous for the Fxn^tm1Mkn targeted mutation and hemizygous for the YG22 transgene.

Allele

Symbol: Tg(FXN)YG22Pook
Name: transgene insertion YG22, Mark A Pook
MGI accession ID: MGI:4412181
Generation method: Transgenic
Attributes: Inserted expressed sequence; Humanized sequence
Synonyms: YG22
Marker symbol: Tg(FXN)YG22Pook
Marker name: transgene insertion YG22, Mark A Pook
Marker synonyms: YG22
Chromosome: UN
Strain of origin: CBA x C57BL/6
Expressed genes: FXN,frataxin,human
Site of expression: The YG22 human FXN YAC transgene contains a single copy of the entire human FXN gene with one GAA trinucleotide repeat sequence of 190 repeats. High levels of human FXN gene product (mRNA or protein) are detected by RT-PCR and western blot analysis.
Molecular note: The transgenic construct consists of a 370kb YAC insert that includes the entire human FXN gene with GAA triplet repeat sequences, and was injected into fertilized CBA X C57BL/6 hybrid fertilized oocytes. Founder line YG22 was generated, showing a reduced transmission rate of 21%, indicating germ-line mosaicism of the transgene, compared to 52% transmission to offspring for founder line YG8. One copy of the FXN gene was detected, and contains a single 190 GAA repeat sequence.
General note: Line YG22 exhibits slightly greater age-related repeat instability than line YG8, with a bias toward repeat expansion.

Allele

Symbol: Fxn^tm1Mkn
Name: targeted mutation 1, Michel Koenig
MGI accession ID: MGI:2177162
Generation method: Targeted
Attributes: Null/Knockout
Synonyms: Frda^-; Frda^del4
Marker symbol: Fxn
Marker name: frataxin
Marker synonyms: CyaY; FA; FARR; FRDA; RGD1565754; X25
Chromosome: 19
Strain of origin: 129/Sv
Expressed genes: Fxn,frataxin,mouse, laboratory
Molecular note: A loxP-flanked PGK-neomycin resistance cassette replaced a genomic DNA fragment containing exon 4, which is highly conserved and often mutated in humans. An additional line was also produced in which the loxP flanked neomycin cassette was removed by Cre mediated recombination, but no distinction was made between these alleles in the original reference. From J:90098: The presence of a human FRDA transgene in hemizygous form in a Frda^tm1Mkn homozygous null background rescues the embryonic lethal phenotype and complements for the loss of endogenous mouse frataxin.