B6.129S4-Mc4r^tm1Lowl/J

Stock number: 032518
Product name: loxTB Mc4r (C57BL/6J)
Research areas: Diabetes and Obesity Research, Neurobiology Research, Research Tools

Description

loxTB Mc4r has a loxP-flanked transcriptional blocker upstream of the Mc4r ATG site - resulting in disrupted Mc4r expression. Exposure to Cre recombinase restores endogenous Mc4r expression. These mutant mice may be useful in studies of neurobiology, obesity, diabetes, hunger/appetite, and fat and energy metabolism.

Detailed description

In an attempt to offer alleles on well-characterized or multiple genetic backgrounds, alleles are frequently moved to a genetic background different from that on which an allele was first characterized. This is the case for these C57BL/6J-congenic loxTB Mc4r mice. It should be noted that the phenotype of these mice could vary from that originally described on a B6;129 mixed genetic background (Stock No. 006414) - see phenotype below. We may modify the C57BL/6J-congenic loxTB Mc4r strain description if necessary as published results become available.

loxTB Mc4r mice have a loxP-flanked transcriptional blocking sequence (loxTB) that prevents normal endogenous gene transcription and translation from the endogenous locus. As such, homozygous mice are devoid of functional mRNA in all tested regions of the brain. Homozygous mice exhibit obesity (Of note: in the JAX colony, some homozygous mice on the mixed B6;129S4 background and on regular chow diet, exhibit obesity), accompanied by hyperphagia, increased snout-anus length and hyperinsulinemia.
The function of this disrupted allele can be restored by the enzymatic activity of Cre recombinase. These mutant mice may be useful in studies of neurobiology, obesity, diabetes, hunger/appetite, and fat and energy metabolism.

When bred to a strain expressing Cre recombinase in the hypothalamus see Stock No. 006395 for example), this mutant mouse strain exhibits as intermediate phenotype in comparison to homozygous null mice.

When crossed to STOCK Slc32a1^tm2(cre)Lowl/J (see Stock No. 016962) Cre recombinase expression in inhibitory GABAergic neuron cell bodies results in offspring that exhibit obesity.

When crossed to B6;129S-Oxt^{tm1.1(cre)Dolsn}/J (see Stock No. 024234) Cre recombinase expression in oxytocin-expressing cells results in offspring that exhibit obesity.

Development

A targeting vector was designed to insert a loxP-flanked transcriptional blocker sequence (loxTB) between the transcriptional start site and ATG of the endogenous gene. The blocker sequence contains an SV40 enhancer, neomycin resistance gene, two HSV-TK polyA sequences, and an additional transcriptional pause signal from the pGL3-control vector. The construct was electroporated into 129S4/SvJae-derived embryonic stem (ES) cells. Correctly targeted ES cells were injected into C57BL/6 blastocysts. Chimeric mice were bred to C57BL/6 mice. Mice heterozygous for the "loxTB Mc4r" allele were bred together for several generations (on a B6;129 mixed genetic background) prior to arrival at The Jackson Laboratory in 2007 as Stock No. 006414. In 2018, some loxTB Mc4r mice were backcrossed to C57BL/6J inbred mice (Stock No. 000664) for at least five generations to generate this C57BL/6J-congenic loxTB Mc4r colony (Stock No. 032518).

A 48 SNP (single nucleotide polymorphism) panel analysis, with 43 markers covering all 19 chromosomes and the X chromosome, as well as 5 markers that distinguish between the C57BL/6J and C57BL/6N substrains, was performed on the rederived living colony at The Jackson Laboratory Repository. One of the 43 markers, on Chromosome 18, was segregating.

Allele

Symbol: Mc4r^tm1Lowl
Name: targeted mutation 1, Bradford B Lowell
MGI accession ID: MGI:3512050
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed); Null/Knockout
Synonyms: loxTB Mc4r; Mc4r^tb
Marker symbol: Mc4r
Marker name: melanocortin 4 receptor
Marker synonyms: BMIQ20; Fatboy; Pkcp
Chromosome: 18
Strain of origin: 129S4/SvJae
Molecular note: A loxP flanked PGK-neomycin selection marker inserted in the 5' UTR created a null allele. Cre recombinase deletes the selection marker, restoring normal activity of the allele. Mice fail to respond to MC4R agonist MTII. This is a null allele that can be "reactivated" by cre recombinase.