Spinal and Bulbar Muscular Atrophy (SBMA) is a polyglutamine disorder caused by a CAG triplet expansion in the androgen receptor gene (AR). The BAC fxAR121 transgene has the human androgen receptor (AR) gene with a floxed exon 1 containing 121 CAG repeats (stabilized with CAA interruptions). Hemizygous and homozygous males are a model of SBMA, with highly representative SBMA motor neuronopathy at ~18-20 weeks of age. Because the mutant exon 1 is flanked by loxP sites, the SBMA phenotype can be prevented/rescued by introducing Cre recombinase. Hemizygous BAC fxAR121 females are viable and fertile with no overt phenotype. Hemizygous and homozygous males are viable but demonstrate reduced fertility. It is recommended to breed hemizygous females with non-carrier or to C57BL/6J inbred males. Both hemizygous and homozygous BAC fxAR121 males develop a progressive neuromuscular phenotype, characterized by weight loss, motor deficits, muscle atrophy and myopathy. Homozygous males demonstrate an earlier and more severe onset, with median survival of ~19 weeks of age in homozygous males and ~42 weeks in hemizygous males. The donating laboratory found that the human AR copy number has increased in this mouse line from ~2 in 2010 to ~3 in 2020 mice, relative to endogenous mouse Ter (<a href="https://pubmed.ncbi.nlm.nih.gov/37269008/">PMID: 37269008</a>). Following Cre recombinase exposure, the mutant AR exon 1 which includes the translational start site, is deleted resulting in loss of hAR*CAG[121] expression. Specifically, when BAC fxAR121 are bred to CMV-Cre mice (see Stock No. <a href="https://www.jax.org/strain/006054">006054</a>), global deletion of hAR*CAG[121] expression in the BAC fxAR121::CMV-Cre progeny prevents neuromuscular disease. Regarding size/stability of the CAG/polyglutamine/polyQ repeat: the donating investigator reports that the BAC fxAR121 transgene CAG repeat was stabilized with CAA interruptions, and backcross generations 1-15 were found to be stable. As such, they did not continue to monitor the number of repeats every generation for this mouse line. When using mouse models where repeat number is subject to germline and somatic instability, and may expand or contract, it is strongly recommended the repeat number be quantified in all the experimental animals. All animals in all experimental groups should carry comparable CAG repeat sizes.

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BAC fxAR121 transgenic mice harbor the human androgen receptor gene with a floxed exon 1 containing 121 CAG repeats. Hemizygous males are a model of Spinal and Bulbar Muscular Atrophy (SBMA), with highly representative SBMA motor neuronopathy ~20 weeks. These mice also allow Cre recombinase-inducible prevention/rescue of the SBMA phenotype. Of note, The Jackson Laboratory breeds and distributes BAC fxAR121 transgenic mice with CAG repeat size range of ~115-116 as determined by Transnetyx assay "GM CAG" quantification (equivalent to CAG repeat size range of ~121-122 via Transnetyx assay "SEQ CAG" quantification).

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Our minimum guarantee for cryorecovery orders is 2 carriers. To ensure that your colony can be rapidly expanded upon arrival, additional carriers may be added to your order.