B6CBA-Tg(HDexon1)62Gpb/3J

Stock number: 006494
Product name: B6CBA-R6/2 (CAG 120 +/- 5)
Research areas: Cardiovascular Research, Diabetes and Obesity Research

Description

These transgenic mice display a progressive neurological phenotype that mimics many of the features of Huntington Disease (HD) in humans, including choreiform-like movements, involuntary stereotypic movements, tremor, and epileptic seizures, as well as nonmovement disorder components, including unusual vocalization. Frequent urination and loss of body weight and muscle bulk occurs through the course of the disease. Neurological developments include Neuronal Intranuclear Inclusions, which contain both the huntingtin and ubiquitin proteins. This line is transgenic for the 5' end of the human HD gene carrying approximately 120 +/- 5 CAG repeat expansions.

Detailed description

This line is transgenic for the 5' end of the human HD gene carrying approximately 120 +/- 5 CAG repeat expansions. The transgene is ubiquitously expressed. Transgenic mice exhibit a progressive neurological phenotype that mimics many of the features of HD, including 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. Neurologically they develop Neuronal Intranuclear Inclusions (NII) which contain both the huntingtin and ubiquitin proteins. Previously unknown, these NII have subsequently been identified in human HD patients. The age of onset of HD symptoms is reported to occur between 9 and 11 weeks. Commonly known as the "R6/2" strain.

Transgenic mice develop hyperglycemia by 12 weeks of age with a corresponding decrease in insulin levels. Pancreatic beta cells develop huntingtin inclusions as early as 7 weeks of age, by 12 weeks more than 95% of beta cells have inclusions. Pancreatic alpha and delta cells also exhibit some inclusions (24% and 6% of cells, respectively) by 12 weeks. Pancreatic islets become hypotonic and beta cells are dramatically reduced in number by 12 weeks. Beta cells contain very few insulin secretory vesicles. (Bjorkquvist M., et al. 2005)

CAG Repeat monitoring:
For R6/2 transgenic mice, the CAG repeat number is subject to germline/somatic instability and may expand/contract. To ensure the stability of the CAG region in Stock Nos. 002810 and 006494, The Jackson Laboratory assays each carrier animal for CAG repeat region size. For additional information, see "General Information for R6/2 transgenic mouse lines" further below.

Pde6b allele monitoring:
The Jackson Laboratory screens/selects the transgenic breeders we use to be wildtype at the Pde6b locus (i.e., not carrying the CBA/J-derived Pde6b^rd1 allele). However, because this strain is maintained by breeding R6/2 transgenic Pde6b^+/+ animals to a B6CBAF1 hybrid at every generation, some progeny will be heterozygous for Pde6b^rd1. Additionally, any other C57BL/6J- or CBA/J-specific mutations (e.g., Nnt^C57BL/6J, etc) could be genotypically heterozygous, homozygous or wildtype in the progeny of these animals.

HDexon1 transgene location in the genome and copy number:
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).

This strain ships with a JAXTag^TM affixed.

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.

Development

The transgene is about 1 kb of the human HD gene and includes the promoter region, exon 1 with 120 +/- 5 CAG repeats. This strain was identified as the R6-2 line in the original publication.

In fall 2006, the B6CBA-Tg(HDexon1)62Gpb/1J colony was shown to have a reduction in the number of CAG repeat units in the transgene (approximately 100-105 CAG repeats), and to exhibit a concomitant decrease in severity and delayed onset in the expected neurological phenotype. The Repository recovered frozen embryos from the HDexon1 line during the winter of 2006/7. The cryo-recovered line has approximately 160 +/- 10 CAG repeats, and onset of HD symptoms occurs between 9 and 11 weeks of age, as originally reported for this strain.

The cryo-recovered line continues as B6CBA-Tg(HDexon1)62Gpb/1J (Stock No. 002810). The phenotypically changed line formerly distributed as Stock No. 002810 is now named B6CBA-Tg(HDexon1)62Gpb/3J (Stock No. 006494) and is maintained with a CAG repeat of 120 +/- 5 repeat units.

CAG Repeat monitoring:
For R6/2 transgenic mice, the CAG repeat number is subject to germline/somatic instability and may expand/contract. To ensure the stability of the CAG region in Stock Nos. 002810 and 006494, The Jackson Laboratory assays each carrier animal for CAG repeat region size. For additional information, see "General Information for R6/2 transgenic mouse lines" in our Detailed Description section.

Pde6b allele monitoring:
The Jackson Laboratory screens/selects the transgenic breeders we use to be wildtype at the Pde6b locus (i.e., not carrying the CBA/J-derived Pde6b^rd1 allele). However, because this strain is maintained by breeding R6/2 transgenic Pde6b^+/+ animals to a B6CBAF1 hybrid at every generation, some progeny will be heterozygous for Pde6b^rd1. Additionally, any other C57BL/6J- or CBA/J-specific mutations (e.g., Nnt^C57BL/6J, etc) could be genotypically heterozygous, homozygous or wildtype in the progeny of these animals.

HDexon1 transgene location in the genome and copy number:
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).

Allele

Symbol: Tg(HDexon1)62Gpb
Name: transgene insertion 62, Gillian Bates
MGI accession ID: MGI:2386951
Generation method: Transgenic
Attributes: Inserted expressed sequence; Humanized sequence
Marker symbol: Tg(HDexon1)62Gpb
Marker name: transgene insertion 62, Gillian Bates
Chromosome: 4
Strain of origin: CBA x C57BL/6
Expressed genes: HTT,huntingtin,human
Molecular note: A human HD fragment containing a polyglutamine-repeat expansion was isolated from a clone derived from a patient with Huntington's disease. The transgene contained approximately 1 kb of 5' UTR region, exon 1 which initially contained 142 CAG repeats, and 262 bp of intron 1. Subsequent analysis showed that the number of CAG repeats was prone to increase when inherited through the male line due to instability in the germline. A range of 141 to 157 was observed. On a background that involves C57BL/6 and CBA, transgenic mice have been observed to carry >(CAG)200 repeat expansions. The insertion site has been localized to a position on mouse chromosome 4 in an intron of predicted gene GM12695. The transgene is ubiquitously expressed.
General note: Transgenic mice exhibit a progressive neurological phenotype that mimics many of the features of HD. Onset of phenotype is apparent from approximately 8 weeks of age based on home cage behavior. Some functional tests indicate the presence of a motor impairment from 5-6 weeks and cognitive impairment from 3 weeks. Epileptic seizures are seen in a small percentage of transgenic mice. A failure to gain weight is more pronounced in males than females. Immunohistochemistry with antibodies raised against the N-terminus of huntingtin reveals aggregates in the form of intranuclear inclusions and neuropil aggregates.

Transgenic mice on a background that involves C57BL/6 and CBA display a progressive neurological phenotype that mimics many of the features of Huntington Disease in humans, including choreiform-like movements, involuntary stereotypic movements, tremor, and epileptic seizures, as well as nonmovement disorder components, including unusual vocalization. Frequent urination, loss of body weight and muscle bulk occurs through the course of the disease. Neurological developments include Neuronal Intranuclear Inclusions (NII), which contain both the huntingtin and ubiquitin proteins (NII have subsequently been identified in human HD patients); the onset of HD symptoms occurs between 9 and 11 weeks.