STOCK Fxn^em2.1Lutzy Tg(FXN)YG8Pook/800J

Stock number: 030395
Product name: Fxn^null::YG8s(GAA)_>800
Research areas: Developmental Biology Research, Neurobiology Research

Description

Fxn^null::YG8s(GAA)_>800 mice are a human FXN YAC transgenic mouse model harboring a global null allele of mouse frataxin (Fxn^null) and the human FXN YAC transgene small repeat YG8s (contracted integration to a single copy of the human FXN gene) with >800 GAA trinucleotide sequence repeats (as of December 2017). This knock-out/transgenic compound mutant strain may be useful in studying Friedreich's Ataxia (FRDA).
Of note, a control strain is available with the same Fxn^null allele and a single copy integration of the Y47 human FXN YAC transgene encoding human frataxin with normal-sized (GAA)₉ repeats: Fxn^null::Y47 (Stock No. 031007).

Detailed description

Fxn^null::YG8s(GAA)_>800 (Stock No. 030395) is a human FXN YAC transgenic mouse model harboring a global knock-out allele of mouse frataxin (Fxn^null) and the YG8 small repeat human FXN YAC transgene (YG8s). The YG8s transgene has a contraction of the original YG8 transgene integration to a single copy. Like other GAA repeat mouse models, the YG8s transgene exhibits somatic GAA repeat instability. As of December 2017, the GAA repeat values were in the 800-899 range - please inquire about the current GAA repeat values. As of November 2018, our breeding of hemizygous mice with noncarrier mice results in 58% of offspring that are hemizygous, and 80% of those hemizygotes stay in the 775-900 range.

Mice that are heterozygous for Fxn^null and hemizygous for the YG8s transgene (also called heterozygous;hemizygous) are viable and fertile with normal lifespan. Mice singly homozygous for the FXN global null allele are embryonic lethal.

When homozygous for the FXN global null allele and hemizygous for the YG8s transgene, Stock No. 030395 mice are called Fxn^null::YG8s(GAA)_>800 (also called homozygous;hemizygous).
The phenotype characterization of Fxn^null::YG8s(GAA)_>800 has not been completed to date [June 2019]. However, they may be expected to have a phenotype similar to that of YG8sR mice (Stock No. 024113) of similar genotype - that is, they are rescued from knock-out lethality and have transgene expression that models the phenotype of Friedreich's Ataxia (FRDA).
Of note, The Jackson Laboratory Stock No. 030395 colony reports the majority of Fxn^null::YG8s(GAA)_>800 mice exhibit hair loss, even when singly housed. [May 2018]
Furthermore, Fxn^null::YG8s(GAA)_>800 exhibit smaller size and large amounts of hair loss compared to wildtype;noncarrier mice. This phenotype lessens to an extent in double homozygous mice, and there is only a slight size difference in heterozygous;hemizygous mice compared to wildtype;noncarrier mice. As the Tg(FXN)YG8Pook trinucleotide repeat count increases, the phenotype also seems to increase in severity as well. [July 2021]
Additionally, The Jackson Laboratory Stock No. 030395 Fxn^null::YG8s(GAA)_>800 mice exhibits cloudy/small eyes with ~3-5% incidence. Furthermore, a small cohort of Fxn^null::YG8s(GAA)_>800 animals with cloudy eyes being used in a brain surgery protocol were examined (n=4; ages 148-165 days old); the resulting histology showed outer retinal degeneration of unknown cause in addition to corneal lesions from trauma due to blindness. [July 2021]

Please see the "Technical Support : Breeding Considerations" section for information on breeding characteristics and which genotype(s) are distributed by The Jackson Laboratory.

Development

These Fxn^null::YG8s(GAA)_>800 mice (Stock No. 030395) harbor a global null allele of mouse frataxin (Fxn^null) and the human FXN YAC transgene small repeat YG8s (contracted integration to a single copy of the human FXN gene) with >800 GAA trinucleotide sequence repeats. The creation of this knock-out/transgenic compound mutant strain is described in more detail below.

The frataxin floxed exon 2 allele Fxn^flox (Fxn^em2Lutzy) was made by Dr. Cat Lutz at The Jackson Laboratory using CRISPR/cas9 endonuclease-mediated genome editing. Some of the C57BL/6J Fxn^flox males (Stock No. 028520) were bred to female B6N.Cg-Tg(Sox2-cre)1Amc/J (Stock No. 014094) to create the frataxin global knockout mice (Stock No. 028040). C57BL/6-congenic Fxn^null mice from Stock No. 028040 were used to generate Stock No. 030395.

The YG8 human FXN YAC transgene was created by Dr. Mark A. Pook by first obtaining the 370 kbp YAC (Y37FA12) that includes the entire human FXN gene with nine GAA repeats [(GAA)₉] at the mutation locus within intron 1 of FXN. The GAA repeat expansion was modified to contain (GAA)₁₉₀. The modified YAC transgene was injected into the pronuclei of (C57BL/6 x CBA)F1 fertilized oocytes. Founder animals were bred to wildtype C57BL/6J mice. Founder line YG8 was established and backcrossed to wildtype C57BL/6J mice. YG8 mice initially contained an expansion of (GAA)_90-190, but was subsequently bred to contain (GAA)_120-220. YG8 mice have two tandem copies of the transgene integrated on mouse chromosome 16. Dr. Pook bred YG8 and Fxn^+/- (Fxn^tm1Mkn) mice together to generate the YG8R human FXN YAC transgenic mouse model (see Stock No. 012253). In 2012, Dr. Pook bred his colony of YG8R with Y47R control transgenic mice (Fxn^+/- mice containing the same human FXN YAC transgene with normal-sized (GAA)₉ repeats; see Stock No. 024097). The resulting animals contained a contraction of the transgene integration to a single copy with (GAA)₁₂₀; these animals were called YG8 small repeat human FXN YAC transgenic rescue mice (YG8sR). Like other GAA repeat mouse models, the YG8sR mice exhibit somatic GAA repeat instability. The GAA repeat size was expanded by selective breeding. By 2014, Dr. Pook had YG8sR animals with ~200 GAA repeats (see Stock No. 024113). By 2016, Dr. Pook sent YG8sR animals with >400 GAA repeats (YG8sR(GAA)_>400) to The Jackson Laboratory. Upon arrival, YG8sR(GAA)_>400 were bred to C57BL/6J inbred mice (Stock No. 000664) for several generations to remove the Fxn^tm1Mkn allele. Those YG8s(GAA)_>400 transgenic mice were subsequently bred with Fxn^em2Lutzy mice from Stock No. 028040. The resulting double mutant mice were selectively bred to have additional GAA expansion (more than 800 GAA repeats as of December 2017). These Fxn^null::YG8s(GAA)_>800 mice are available as Stock No. 030395.

Allele

Symbol: Tg(FXN)YG8Pook
Name: transgene insertion YG8, Mark A Pook
MGI accession ID: MGI:3797739
Generation method: Transgenic
Attributes: Inserted expressed sequence; Humanized sequence
Marker symbol: Tg(FXN)YG8Pook
Marker name: transgene insertion YG8, Mark A Pook
Chromosome: UN
Strain of origin: CBA x C57BL/6
Expressed genes: FXN,frataxin,human
Site of expression: The human FXN YAC transgene contains the promoter and coding regions of human FXN with GAA trinucleotide sequence repeats. Individual strains at The Jackson Laboratory have specific variants of this this transgene. See Detailed Description section for greater detail of transgene insertion site, copy number, GAA repeat values and expression levels.
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 YG8 was established, carrying 2 tandem copies of the human FXN gene with two GAA trinucleotide repeat sequences of 82 and 190 repeats. This line displayed a transmission rate of 52% to offspring.
General note: Line YG22 exhibits slightly greater age-related repeat instability, with a bias toward repeat expansion.

Allele

Symbol: Fxn^em2.1Lutzy
Name: endonuclease-mediated mutation 2.1, Cathy Lutz
MGI accession ID: MGI:5825278
Generation method: Endonuclease-mediated
Attributes: Null/Knockout
Marker symbol: Fxn
Marker name: frataxin
Chromosome: 19
Strain of origin: C57BL/6J
Site of expression: Cardiac and skeletal muscle.
Molecular note: CRISPR/Cas9 genome editing was used to introduce loxP sites flanking exon 2. Cre-mediated recombination removed exon 2.