B6.129S1(Cg)-Htt^tm2Mem/20ChdiJ

Stock number: 027411
Product name: B6J.HdhQ20 ; HttQ20 ; CHDI-81003005
Research areas: Mouse/Human Gene Homologs, Neurobiology Research, Research Tools

Description

The C57BL/6J-congenic HdhQ20 knock-in mice (B6J.Hdh^Q20) mice have chimeric mouse Htt : human HTT exon 1 (Hdh:HD exon 1) encoding the human version of the polyglutamine/polyproline-rich segment with 18 CAG repeats [(CAG)₁₈CAACAG]. These B6J.HdhQ20 knock-in mice may be useful for studying Huntington's disease, specifically to investigate the influence of CAG size on the desired outcome measures.

Detailed description

Stock No. 027411 was formerly associated with CHDI Foundation colony Stock No. 370504 [CHDI-81003005].

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).
The HdhQ20 knock-in allele (Hdh^Q20) has a chimeric mouse:human huntingtin exon 1 (Hdh:HD exon 1) encoding the human version of the polyglutamine/polyproline-rich segment with 18 CAG repeats [(CAG)₁₈CAACAG]. The polyglutamine stretch in the mutant huntingtin product, as denoted in the name of the Hdh^Q20 knock-in allele, is two residues longer than the number of CAG units in the repeat due to invariant, penultimate exon 1 CAA,CAG codons immediately downstream. The CAG repeat number in the Hdh^Q20 knock-in allele is reported to be stable (see note on CAG stability below). Mutant mice accurately express the mouse/human hybrid huntingtin protein. Homozygous and heterozygous mice are viable and fertile with normal lifespans.

This Huntington's disease mouse model is available by way of a collaborative effort between CHDI Foundation, Dr. Marcy E. MacDonald (Massachusetts General Hospital) and The Jackson Laboratory.

While pure CAG sequences in exon 1 may be subject to germline or somatic instability, and may expand or contract, the CAG repeat number in the Hdh^Q20 knock-in allele is reported to be stable. 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 HdhQ20 knock-in allele (Hdh^Q20) was designed by Dr. Marcy E. MacDonald (Massachusetts General Hospital) to have a chimeric Hdh:HD exon 1 encoding the human version of the polyglutamine/polyproline-rich segment with 18 CAG repeats [(CAG)₁₈CAACAG]. Specifically, a 296 bp fragment (172 bp of exon 1 and 124 bp of intron 1) of the mouse huntingtin gene (Htt; HD or Hdh) was replaced with a human HTT sequence (232 bp of exon 1 containing 18 CAG repeats [(CAG)₁₈CAACAG] and 268 bp of intron 1). The endogenous mouse consensus 5' splice donor sequence remains in intron 1. A floxed PGK-neo cassette inserted 950 bp upstream of the ATG initiation codon was removed by exposure to Cre recombinase. The targeting vector was microinjected into 129S1/Sv-Kitl⁺-derived R1 embryonic stem (ES) cells. For all the Hdh knock-in lines, the male founders were bred to CD1 females and the lines were maintained on a mixed 129SvEv/CD1 genetic background.

The HdhQ20 knock-in mice were backcrossed with C57BL/6J inbred mice for 5-10 generations, sent to the CHDI Foundation, and then backcrossed an additional ten generations with C57BL/6J inbred mice (Stock No. 000664) to create the C57BL/6J-congenic colony (B6J.HdhQ20 or B6J.Hdh^Q20), called CHDI Foundation colony Stock No. 370504 [CHDI-81003005]. In 2015, heterozygous animals with 18 CAG repeat length were sent from the CHDI Foundation colony to The Jackson Laboratory Repository, from which B6J.HdhQ20 heterozygotes are available as Stock No. 027411.

Allele

Symbol: Htt^tm2Mem
Name: targeted mutation 2, Marcy E MacDonald
MGI accession ID: MGI:1861703
Generation method: Targeted
Attributes: Humanized sequence
Marker symbol: Htt
Marker name: huntingtin
Chromosome: 5
Strain of origin: (129X1/SvJ x 129S1/Sv)F1-Kitl⁺
Molecular note: This allele carries 18 CAG repeat units, with 20 glutamines, in the first exon of the endogenous gene, modeling the number of CAG repeats found in the human Hdh. It is a derivative of Hdh^tm6Mem in which the neo cassette has been removed via cre-mediated recombination.