B6.129P2(Cg)-Cx3cr1^{tm2.1(cre/ERT2)Litt}/WganJ

Stock number: 021160
Product name: Cx3cr1^CreER
Research areas: Neurobiology Research, Research Tools

Description

Cx3cr1^CreER knock-in/knock-out mice express a Cre-ERT2 fusion protein and EYFP in microglia in the brain. These mice may have applications in studies requiring conditional gene manipulation in central nervous system microglia, as well as other Cx3cr1-expressing myeloid cell populations.

Detailed description

Cx3cr1^CreER knock-in/knock-out mice express a Cre-ERT2 fusion protein and an enhanced yellow fluorescent protein (EYFP) from endogenous Cx3cr1 promoter/enhancer elements. Insertion of the Cre-ERT2 and EYFP knocks out endogenous CX3CR1 expression. EYFP immunofluorescence is observed in Cx3cr1-expressing microglia in the brain, mimicking endogenous gene expression patterns. 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.

Of note, Sahasrasbuddhe et al (PMID 35045285) have determined that tamoxifen-induced cre activation (administered P3-P5) causes microglial activation, IFN1 signaling, and increased phagocytosis resulting  in aberrant synaptic pruning in early postnatal microglia. Tamoxifen induction in adult microglia does not result in DNA damage.

When bred to mice containing loxP-flanked STOP cassette upstream of a red fluorescent protein (DsRed) sequence, few DsRed+ microglia (0.3% ± 0.01%) were found in the brain in the absence of tamoxifen. After 5 days of tamoxifen treatment, 93.9% of CX3CR1-EYFP+ microglia in CX3CR1^CreER/+:R26^DsRed/+ mice were found to coexpress YFP and DsRed.

Of note, The Jackson Laboratory also has available Cx3cr1^CreER mice without EYFP expression (Stock No. 020940).

Development

A targeting vector was designed to replace exon 2 of the chemokine (C-X3-C) receptor 1 (Cx3cr1) gene with a CreERT2 (Cre-ERT2; Cre recombinase fused to a G400V/M543A/L544A triple mutation of the human estrogen receptor ligand binding domain) coding sequence, followed by an internal ribosome entry site (IRES) and an enhanced yellow fluorescent protein (EYFP). A frt-flanked neomycin resistance cassette, in reverse orientation to the gene, was also inserted downstream of the EYFP sequence. This construct was electroporated into 129P2/OlaHsd-derived E14.1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts and chimeric males were bred with C57BL/6J females expressing Flp recombinase under the control of the Rosa26 locus to excise the neomycin resistance sequence. The resulting Cx3cr1^CreER mice were bred to C57BL/6J mice for at least 12 generations. Upon arrival at The Jackson Laboratory, mice were bred with C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the colony.

Allele

Symbol: Cx3cr1^{tm2.1(cre/ERT2)Litt}
Name: targeted mutation 2.1, Dan R Littman
MGI accession ID: MGI:5450813
Generation method: Targeted
Attributes: Recombinase-expressing; Reporter; 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: Cx3cr1^CreER mice express a Cre-ER fusion protein and EYFP in monocytes, dendritic cells, NK cells, and brain microglia.
Molecular note: A targeting vector was designed to replace exon 2 of the chemokine (C-X3-C) receptor 1 (Cx3cr1) gene with a cre/ERT2 (cre recombinase fused to an estrogen receptor ligand binding domain) coding sequence, followed by an internal ribosome entry site (IRES) and an enhanced yellow fluorescent protein (EYFP). A frt-flanked neomycin resistance cassette, in reverse orientation to the gene, was also inserted downstream of the EYFP sequence. Flp-mediated recombination excised the neomycin resistance sequence.