B6.Cg-Fxn^em2Lutzy Fxn^em2.1Lutzy Tg(Ckmm-cre)5Khn/J

Stock number: 029720
Product name: Fxn^flox/null::MCK-Cre
Research areas: Cardiovascular Research, Neurobiology Research, Research Tools

Description

Fxn^flox/null::MCK-Cre mice have a Cre-conditional frataxin allele, a global knockout frataxin allele and a cardiac/skeletal muscle-specific Cre recombinase transgene - and are useful in studying Friedreich's Ataxia.
The Fxn^flox/null::MCK-Cre genotype is compound heterozygous at the frataxin locus (floxed exon 2 and global knockout on respective homologous chromosomes) and hemizygous for MCK-Cre. Due to early-onset cardiomyopathy, Fxn^flox/null::MCK-Cre are distributed as close to 4-6 weeks of age as possible.
We also distribute phenotypically-normal parental lines:
i. Stock No. 028520: C57BL/6J-congenic Fxn^em2Lutzy (homozygous frataxin floxed exon 2)
ii. Stock No. 029100: C57BL/6-congenic Fxn^em2.1Lutzy Tg(Ckmm-cre)5Khn (heterozygous frataxin global knockout and homozygous MCK-Cre).
These breeders produce the affected Fxn^flox/null::MCK-Cre genotype at 1/2 frequency.
Our preclinical efficacy testing services offer scientific expertise and an array of target-based and phenotype-based outcome measures, both in vivo and at endpoint, for flexible study designs and assay development in mouse models of Friedreich's Ataxia. See our full service platform.

Detailed description

Mice that are compound heterozygotes at the frataxin locus (Fxn^flox/null) harbor the frataxin floxed exon 2 allele (Fxn^em2Lutzy) on one homologous chromosome, and the frataxin global knockout allele (Fxn^em2.1Lutzy) on the other homologous chromosome. The MCK-Cre transgene (Tg(Ckmm-cre)5Khn) has Cre recombinase expression directed to cardiac and skeletal muscle.

The Fxn^flox/null::MCK-Cre mice (Stock No. 029720) develop progressive cardiomyopathy due to frataxin protein deficiency in heart and skeletal muscle. Mutants exhibit peak body weight around 60 days of age and have a mean survival of 77 days of age [September 2020]. Cardiomyopathic phenotype is characterized by decreased heart rate and ejection fraction, as well as fractional shortening distinguishable from non-mutant littermates by approximately 7 weeks of age. Left ventricular mass is significantly increased compared to non-mutant littermates by 9 weeks of age.

Development

These Fxn^flox/null::MCK-Cre mice (Stock No. 029720) harbor a floxed allele of mouse frataxin Fxn^flox (Fxn^em2Lutzy ; from Stock No. 028520), a global null allele of mouse frataxin Fxn^null (Fxn^em2.1Lutzy; from Stock No. 028040) and the MCK-Cre transgene with the Ckmm promoter driving Cre recombinase expression (Tg(Ckmm-cre)5Khn; from Stock No. 006475). Each component is described 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. Plasmids encoding a signal guide RNA designed to introduce loxP sites flanking exon 2 in the Fxn gene and the CRISPR/cas9 nuclease were introduced into the cytoplasm C57BL/6J-derived fertilized eggs with well recognized pronuclei. Correctly targeted embryos were transferred to pseudopregnant females. Correctly targeted pups were identified by sequencing and PCR. Mice from founder 466 were further bred to C57BL/6J inbred mice (Stock No. 000664) to develop the frataxin floxed exon 2 colony as Stock No. 028520. Fxn^flox mice from Stock No. 028520 were used to generate Stock No. 029720.

To generate the global knockout allele Fxn^null (Fxn^em2.1Lutzy), male mice carrying the floxed exon 2 allele (from Stock No. 028520) were bred to female B6N.Cg-Tg(Sox2-cre)1Amc/J (Stock No. 014094). The resulting mice (exon 2 deleted from germline) were further bred to C57BL/6J to breed out the Cre recombinase transgene. Heterozygous intercrosses were performed to confirm the embryonic lethality of the null allele. Mice heterozygous for this frataxin global knockout allele are available as Stock No. 028040. Fxn^null mice from Stock No. 028040 were used to generate Stock No. 029720.

The Tg(Ckmm-cre) transgene (MCK-Cre) was designed by Dr. C. Ronald Kahn (Joslin Diabetes Center) to have a Cre recombinase cDNA sequence (with a SV-40 large T antigen nuclear localization signal and polyA signal) inserted in place of the translation initiation site of the Ckm gene. C57BL/6-congenic MCK-Cre line 5 mice from Stock No. 006475 were used to generate Stock No. 029720.

Allele

Symbol: Tg(Ckmm-cre)5Khn
Name: transgene insertion 5, C Ronald Kahn
MGI accession ID: MGI:2182095
Generation method: Transgenic
Attributes: Recombinase-expressing
Marker symbol: Tg(Ckmm-cre)5Khn
Marker name: transgene insertion 5, C Ronald Kahn
Chromosome: UN
Strain of origin: FVB
Expressed genes: cre,cre recombinase,bacteriophage P1
Site of expression: skeletal and cardiac muscle
Molecular note: A 6.5 kb genomic DNA fragment of the Ckmm gene containing the promoter and enhancer 1, untranslated exon 1, 3kb of intron 1 including the enhancer 2 region, and the first 16 bp of exon 2 drives expression of a modified cre with an SV40 large T antigen nuclear localization signal. Expression is directed to the heart and skeletal muscle.

Allele

Symbol: Fxn^em2Lutzy
Name: endonuclease-mediated mutation 2, Cathy Lutz
MGI accession ID: MGI:5825257
Generation method: Endonuclease-mediated
Attributes: Conditional ready (e.g. floxed); No functional change
Marker symbol: Fxn
Marker name: frataxin
Chromosome: 19
Strain of origin: C57BL/6J
Molecular note: CRISPR/Cas9 genome editing is used to introduce loxP sites flanking exon 2.

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.