B6J.129S1-Htt^tm1Mfc/140ChdiJ

Stock number: 027409
Product name: B6J.CAG 140 KI ; B6J.CAG140 knock-in ; Q140 on C57BL/6J background ; CHDI-81003002
Research areas: Neurobiology Research, Research Tools

Description

The C57BL/6J-congenic CAG140 knock-in (CAG 140 KI) allele encodes the human HTT exon 1 sequence with ~140 repeats of a pure CAG tract replacing the mouse Htt exon 1. These B6J.CAG 140 KI mice may be useful for studying Huntington's disease.

Detailed description

Stock No. 027409 was formerly associated with CHDI Foundation colony Stock No. 370625 [CHDI-81003002].

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 CAG140 knock-in (CAG 140 KI) allele replaces mouse Htt exon 1 with the human HTT exon 1 sequence with ~140 repeats of a pure CAG tract [(CAG)nCAACAG, encoding polyglutamine (no arginine codon)]. The CAG repeat number is subject to germline and somatic instability, and may expand or contract. Mutant mice have mouse/human hybrid protein expression in cerebellum and forebrain at similar levels of endogenous protein. Homozygous and heterozygous mice are viable and fertile with normal lifespans. Homozygous mice may exhibit motor deficits (as evidenced in rotarod performance, gait/locomotion and exploratory behavior), with varying onset and severity depending on the protocols used. Homozygotes may have decreased body weight from 26 weeks of age. Heterozygous mice may exhibit relatively mild behavioral deficits with a late age of onset.

This Huntington's disease mouse model is available by way of a collaborative effort between CHDI Foundation, Dr. Marie-Francoise Chesselet (University of California, Los Angeles) and The Jackson Laboratory.

In these mutant mice, the CAG repeat number is subject to germline and somatic instability, and may expand or contract. 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 CAG140 knock-in (CAG 140 KI) allele was designed by Dr. Marie-Francoise Chesselet (University of California, Los Angeles). A fragment extending from 18 bp upstream of the polyglutamine stretch in huntingtin (Htt; HD or Hdh) exon 1 to 100 bp into intron 1 was replaced with human HTT sequence containing 140 repeats of a pure CAG tract [(CAG)nCAACAG, encoding polyglutamine (no arginine codon)]. A floxed neo cassette was retained 1.3 kbp upstream of exon 1. The targeting vector was microinjected into 129S1/Sv-Oca2⁺ Tyr⁺ Kitl⁺-derived W9.5/W95 embryonic stem (ES) cells. The CAG 140 KI mice were backcrossed with C57BL/6J inbred mice (Stock No. 000664) at least four or five generations to create the C57BL/6J-congenic colony (B6J.CAG 140 KI), called CHDI Foundation colony Stock No. 370625 [CHDI-81003002]. In 2014, heterozygous animals with ~146 CAG repeat length were sent from the CHDI Foundation colony to The Jackson Laboratory Repository, from which B6J.CAG 140 KI heterozygotes are available as Stock No. 027409.

Allele

Symbol: Htt^tm1Mfc
Name: targeted mutation 1, Marie-Francoise Chesselet
MGI accession ID: MGI:2675580
Generation method: Targeted
Attributes: Humanized sequence
Marker symbol: Htt
Marker name: huntingtin
Chromosome: 5
Strain of origin: 129S1/Sv-Oca2⁺ Tyr⁺ Kitl⁺
Molecular note: A fragment extending from 18 bp upstream of the polyglutamine stretch in exon 1 to 100 bp into intron 1 was replaced with human HD sequence containing 140 CAG repeats. A floxed neo cassette was retained 1.3 kb upstream of exon 1. Western blot analysis of homozygous mutant cerebellum and forebrain tissues identified protein corresponding with the mouse/human hybrid protein. Similar levels of mutant and endogenous protein were observed. The repeat number is not stable and may expand or contract.