Stock No. 027425 was formerly associated with CHDI Foundation colony Stock No. 908766 [CHDI-81001008].
Huntington's disease (HD) is an autosomally dominant, fatal neurodegenerative disorder characterized by uncontrolled movements, psychiatric disturbances and cognitive impairment. HD is caused by an unstable trinucleotide (polyglutamine) repeat expansion in the huntingtin gene (HTT; HD or Hdh). For R6/2 transgenic mice, the CAG repeat number is subject to germline/somatic instability and may expand/contract. For additional information on this, see "General Information for R6/2 transgenic mouse lines" below.
Stock No. 027425: The DBA/2J-congenic R6/2 transgenic mouse line with ~350 CAG repeat expansions, called D2.R6/2 (CAG ~350) mice, are not fully characterized to date (April 2014).
However, they may exhibit a similar or delayed phenotype compared to that of R6/2 mice with ~160 CAG repeats on a (C57BL/6 x CBA)F1 genetic background. Those B6CBA.R6/2 (CAG 160) transgenic mice are described and available as Stock No. 002810. Briefly, B6CBA.R6/2 (CAG 160) mice exhibit a progressive neurological phenotype that mimics many of the features of HD. This includes early-onset (9-21 weeks of age), choreiform-like movements, involuntary stereotypic movements, tremor and epileptic seizures, as well as nonmovement disorder components (including unusual vocalization). They urinate frequently and exhibit loss of body weight and muscle bulk through the course of the disease. They develop neuronal intranuclear inclusions (huntingtin and ubiquitin), pancreatic beta cell inclusions (huntingtin) and hyperglycemia. R6/2 mice may exhibit metabolic deficits that prevent them from controlling body temperature as efficiently as their wildtype (noncarrier) littermates. Hemizygous mice have shortened lifespan (median survival may be ~20 weeks or less) with females living slightly longer. Hemizygous females are not fertile. Hemizygous males have a short (3-4 week) breeding window, and only about half are fertile.
This Huntington's disease mouse model is available by way of a collaborative effort between CHDI Foundation, Dr. Gillian P. Bates (United Medical and Dental School, London) and The Jackson Laboratory.
Transgene Insertion Information:
The HDexon1 transgene functions as single copy insertion. Sequence analysis identified its insertion site within an intron of the predicted gene Gm12695 on mouse chromosome 4 (chr4:96,409,585-96,414,930 [assembly NCBI 37/mus musuculus 9)], and the transgene is flanked by two rearranged sequences that do not contain the full exon 1 encoding DNA (Cowin et al. 2011 PLoS ONE 6(12):e28409). Additionally, a segment of Gram-positive bacterial sequence (likely originating from cloning vector contamination) is inserted just upstream of the HTT promoter that drives the expression of the intact copy. Transgene insertion also resulted in a 5.4 kbp deletion of mouse chromosomal DNA near the integration site (Chiang et al. 2012 Nat Genet. 44(4):390-7). As of January 2017, the function of predicted gene Gm12695 is unknown. It is normally expressed at negligible levels in mouse brain. The transgene insertion (in antisense orientation to Gm12695 transcription) results in increased cortical expression of a partial Gm12695 fragment (exons 8-11) - and this transcript is shown to have significant expression among the extensive network of differentially expressed genes associated with the R6/2 model, including those regulating synaptic transmission, cell signaling and transcription (Jacobsen et al. 2017 Sci Rep. 7:41120).
General Information for R6/2 transgenic mouse lines:
The R6/2 transgenic mouse lines express a transgene encoding the 5' end of human HTT with different lengths of CAG repeat expansions. The CAG repeat number is subject to germline and somatic instability, and may expand or contract. The phenotype of R6/2 animals varies greatly as a function of CAG repeat size and, similar to what is observed in humans, R6/2 transgenic mice may exhibit higher incidence of CAG repeat expansion when the transgene is transmitted via paternal inheritance. Interestingly, the copy:phenotype relationship is not linear for R6/2 mice, nor does a large CAG repeat number necessarily lead to an earlier onset and more severe phenotype. Genetic background may also lead to variations in disease severity/progression.
When using lines with unstable CAG repeat length, it is strongly recommended the CAG repeat number be quantified in all the experimental animals - all animals in all experimental groups should carry comparable CAG repeat sizes. CAG repeat sizing of HD mice should be done using high-resolution methods - as assays based on agarose gel electrophoresis typically do not provide sufficient resolution to accurately measure CAG repeat numbers. If labs do not have access to the appropriate equipment for determining CAG repeat length, CAG repeats can be evaluated on a fee-for-service basis by Laragen, Inc.
R6/2 animals on a (C57BL/6 x CBA)F1 genetic background are available with CAG expansion sizes of ~120 and ~160.
B6CBA.R6/2 (CAG 120) mice are Stock No. 006494
B6CBA.R6/2 (CAG 160) mice are Stock No. 002810
R6/2 animals on a C57BL/6J genetic background are available with CAG expansion sizes of ~116, ~168 and ~251.
B6J.R6/2 (CAG 116) mice are Stock No. 027419 [CHDI-81001001]
B6J.R6/2 (CAG 168) mice are Stock No. 027421 [CHDI-81001003]
B6J.R6/2 (CAG 251) mice are Stock No. 027423 [CHDI-81001005]
R6/2 animals on a DBA/2J genetic background are available with the different CAG expansion sizes listed below.
D2.R6/2 (CAG ~180) mice are Stock No. 027422 [CHDI-81001004]
D2.R6/2 (CAG ~380) mice are Stock No. 027424 [CHDI-81001006]
D2.R6/2 (CAG ~350) mice are Stock No. 027425 [CHDI-81001008]
