B6.129P2(C)-Cx3cr1^{tm2.1(cre/ERT2)Jung}/J

Stock number: 020940
Product name: Cx3cr1^CreER
Research areas: Neurobiology Research, Research Tools

Description

Cx3cr1^CreER knock-in/knock-out mice express tamoxifen-inducible Cre recombinase under the direction of the Cx3cr1 promoter in the mononuclear phagocyte system making them useful for fate-mapping studies of the monocyte and macrophage compartment, as well as microglia.

Detailed description

Cx3cr1^CreER knock-in/knock-out mice express a Cre-ER fusion protein from endogenous Cx3cr1 promoter/enhancer elements. Insertion of the Cre-ER fusion protein knocks out endogenous CX3CR1 expression. CX3CR1 is a chemokine receptor expressed in the mononuclear phagocyte system, as well as microglia. Homozygous mice are viable and fertile. When Cx3cr1^CreER mice are bred with mice containing loxP-flanked sequence, tamoxifen-inducible, Cre-mediated recombination will result in deletion of the floxed sequences.

For example, when bred to B6.129X1-Gt(ROSA)26Sor^tm1(EYFP)Cos/J mice (Stock No. 006148), cre-mediated recombination results in yellow fluorescent protein expression in microglia, and intestinal and kidney macrophages.

Additionally, very low levels of Cre activity may be present prior to introduction of tamoxifen - but the Cre activity after tamoxifen are significantly greater than those baseline levels. As such, it is recommended that researchers include tamoxifen-negative controls to establish any baseline levels of Cre activity in their experiments. For example, when Cx3cr1^CreER are bred to the dual fluorescent reporter line mT/mG (Stock No. 007676), the resulting mice had some basal Cre activity (GFP expression) in a fraction of microglia prior to tamoxifen treatment, but the Cre activity upon tamoxifen treatment was significantly greater (almost completely restricted to microglia).

Of note, The Jackson Laboratory also has available Cx3cr1^CreER mice with EYFP expression (Stock No. 021160).

Development

A targeting vector was designed to replace exon 1 of the chemokine (C-X3-C) receptor 1 (Cx3cr1) gene with a CreER (Cre recombinase fused to an estrogen receptor ligand binding domain) coding sequence and a loxP-flanked neomycin (neo) resistance cassette. This construct was electroporated into 129P2/OlaHsd-derived E14 embryonic stem (ES) cells. Chimeras were made by ES cell aggregation with eight-cell stage embryos and chimeric mice were bred with Tg(Pgk1-cre)1Lni mice to delete the neo cassette. Resulting offspring were bred to remove the cre-expressing transgene, and progeny were bred with C57BL/6JOlaHsd inbred mice for at least 10 generations. Upon arrival at The Jackson Laboratory, mice were bred to C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the colony.

Allele

Symbol: Cx3cr1^{tm2.1(cre/ERT2)Jung}
Name: targeted mutation 2.1, Steffen Jung
MGI accession ID: MGI:5467985
Generation method: Targeted
Attributes: Recombinase-expressing; Inducible
Marker symbol: Cx3cr1
Marker name: chemokine (C-X3-C motif) receptor 1
Chromosome: 9
Strain of origin: 129P2/OlaHsd
Expressed genes: cre/ERT2,Cre recombinase and estrogen receptor 1 (human) fusion gene,
Site of expression: Mice express tamoxifen-inducible Cre recombinase in the mononuclear phagocyte system.
Molecular note: A cre/ERT2 cassette with a floxed neo gene was inserted by RedE/T recombineering into a BAC containing the Cx3cr1 locus, replacing the coding exon of Cx3cr1. Properly targeted ES cells were aggregated with 8-cell embryos to generate chimeras. Chimeras were backcrossed to C57BL/6 mice. Tne neo was excised by crossing the animals to a cre deleter strain (Tg(Pgk1-cre)1Lni).