B6.Cg-Mc3r^tm1Butl/J

Stock number: 017866
Research areas: Cardiovascular Research, Diabetes and Obesity Research, Metabolism Research, Research Tools

Description

When these Mc3r^-/- floxed-STOP mice are bred to mice that express Cre recombinase, resulting bi-allelic offspring will have a floxed-STOP sequence deleted in cre-expressing tissues, allowing Mc3r expression. These mice may be useful when studying metabolism and obesity.

Detailed description

These Mc3r^-/- mutant mice possess a floxed STOP-neo cassette upstream of the start codon, and an IRES-GFP cassette downstream of the stop codon of the melanocortin 3 receptor (Mc3r) gene. MC3R is a G-protein coupled receptor for the melanocyte-stimulating hormone. It is expressed in the hypothalamic and limbic regions of the brain and in some peripheral tissues including the renal cortex and medulla, and the immune system. MC3R contributes to the regulation of body composition, salt excretion, immune function, and energy homeostasis. Homozygous MC3R^-/- males are fertile while homozygous females are poor breeders. These floxed-STOP mice exhibit increased susceptibility to diet-induced obesity, with increased fat mass and decreased lean mass when fed a standard chow diet. These mice can also exhibit increased circulating insulin and leptin levels, changes in serum triglyceride levels, changes in the respiratory exchange ratio (indicating altered whole body substrate preference), and decreased physical activity. When these mutant mice are bred to mice that express Cre recombinase, resulting offspring will have the STOP cassette deleted, allowing MC3R expression in cre-expressing tissues.

For example, when bred to B6.Cg-Tg(Nes-cre)1Kln/J (Stock No. 003771) expressing Cre in the nervous system, the resulting offspring display a partial rescue of the obesity phenotype.

When bred to FVB-Tg(Nr5a1-cre)2Lowl/J (Stock No. 006364) expressing Cre in steroidogenic factor-1 (SF1)-positive neurons, the resulting offspring exhibit improvements in metabolic homeostasis.

The donating investigator reports that although an IRES-GFP is present in the allele, expression is too low to detect.

Development

A targeting vector was designed to insert a floxed STOP-neo cassette was placed upstream of the translational start site of the melanocortin 3 receptor (Mc3r) gene. An Internal ribosome entry site (IRES) fused to an enhanced green fluorescent protein (AcGFP1) was placed downstream of open reading frame. The construct was electroporated into C57BL/6-derived Bruce-4 embryonic stem (ES) cells. Correctly targeted ES cells were injected into B6(Cg)-Tyr^c-2J/J blastocysts and resulting chimeric males were bred to B6(Cg)-Tyr^c-2J/J females. The donating investigator stated that these mice were backcrossed to C57BL/6J (see SNP note below). Upon arrival, mice were bred to C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the colony.

A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 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. While the 27 markers throughout the genome suggested a C57BL/6 genetic background, 3 of 5 markers that determine C57BL/6J from C57BL/6N were found to be segregating. These data suggest the mice sent to The Jackson Laboratory Repository were on a C57BL/6N genetic background.

Allele

Symbol: Mc3r^tm1Butl
Name: targeted mutation 1, Andrew A Butler
MGI accession ID: MGI:5302394
Generation method: Targeted
Attributes: Conditional ready (e.g. floxed); No functional change
Marker symbol: Mc3r
Marker name: melanocortin 3 receptor
Chromosome: 2
Strain of origin: B6.Cg-Thy1^a
Molecular note: A loxP-stop-loxP cassette was inserted just upstream of the initiation codon and an IRES-AcGFP1was inserted after the open reading frame via homologous recombination.