loxTB Mc4r mice are also available on a C57BL/6J genetic background as Stock No. 032518.
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.
Bradford B. Lowell, Beth Israel Deaconess Med Cntr (Harvard)
The mice have a loxp-flanked transcriptional blocking (loxTB) sequence 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, accompanied by hyperphagia, increased snout-anus length and hyperinsulinemia. In 2018, The Jackson Laboratory colony, on the mixed B6;129S4 background and maintained on standard chow diet, shows that homozygous mice are significantly heavier than sex-matched wildtype controls by approximately 6-8 weeks of age (more obvious for female homozygotes at a younger age), and obesity (30g) is apparent at approximate 7 weeks of age for homozygous males and approximately 10 weeks of age for homozygous females.
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 Slc32a1tm2(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-Oxttm1.1(cre)Dolsn/J (see Stock No. 024234) Cre recombinase expression in oxytocin-expressing cells results in offspring that exhibit obesity.
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. Mutant mice heterozygous for the "loxTB Mc4r" allele were bred together and maintained as such prior to arrival at The Jackson Laboratory.
|Allele Name||targeted mutation 1, Bradford B Lowell|
|Allele Type||Targeted (Conditional ready (e.g. floxed), Null/Knockout)|
|Allele Synonym(s)||loxTB Mc4r; Mc4rtb|
|Gene Symbol and Name||Mc4r, melanocortin 4 receptor|
|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.|
|Mutations Made By|| |
Bradford Lowell, Beth Israel Deaconess Med Cntr (Harvard)
Although homozygous mice are viable and fertile, the donating investigator breeds heterozygous mice together to generate homozygous, heterozygous, and wildtype mice.
Of note: In 2018, The Jackson Laboratory colony, on the mixed B6;129S4 background and maintained on standard chow diet, shows that homozygous mice are significantly heavier than sex-matched wildtype controls by approximately 6-8 weeks of age (more obvious for female homozygotes at a younger age), and obesity (30g) is apparent at approximate 7 weeks of age for homozygous males and approximately 10 weeks of age for homozygous females.
When using the loxTB Mc4r mouse strain in a publication, please cite the originating article(s) and include JAX stock #006414 in your Materials and Methods section.
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