Cx3cr1-iCre Mice

The start and stop codons of the mouse Cx3cr1 gene are both located in Exon 2, which is replaced by an iCre recombinase expression element through gene editing.

a. Method

Cx3cr1-iCre mice were crossed with Rosa26-LSL-tdTomato mice to generate double heterozygous offspring. In these offspring, Cre recombinase-mediated recombination would result in the expression of tdTomato protein in Cre-positive cells. Tissues from the brain, skin, liver, kidney, intestines, spleen, and lungs were collected from 7-week-old offspring mice and analyzed by immunofluorescence staining to detect the distribution of tdTomato protein signal to determine the expression pattern of Cre recombinase.

b. Genotype

Cre+: Cx3cr1-iCre[KI/+];Rosa26-LSL-tdTomato[CKI/+]
Cre-: Rosa26-LSL-tdTomato[CKI/+]

c. Result

1. Expression of Cre recombinase in the brain

Figure 1. Immunofluorescence staining of brain tissue. In Cre+ mice, brain tissue exhibits a large amount of tdTomato protein signal (red), which co-localizes with the expression of the microglial marker IBA1 (green). This indicates a high level of Cre recombinase expression in brain microglia. In contrast, control (Cre-) mice show no detectable expression of tdTomato red fluorescence, indicating an absence of Cre recombinase expression.

2. Expression of Cre recombinase in the skin

Figure 2. Immunofluorescence staining of brain tissue. In Cre+ mice, there is a strong expression of tdTomato protein (red) in skin tissue, indicating the presence of Cre recombinase expression in this location, possibly in macrophages. In contrast, the red fluorescence in the control (Cre-) group is due to leakage from the Rosa26-LSL-tdTomato strain of mice (internal data shows that Rosa26-LSL-tdTomato mice have a chance of slight leakage in the skin, but no leakage in other parts).

3. Expression of Cre recombinase in the lung, kidney, liver, and intestine

Figure 3. Immunofluorescence staining of lung, kidney, liver, and intestinal tissues. In Cre+ mice, tdTomato protein expression is observed in some tissues of the lungs, kidneys, liver, and intestines, indicating the presence of Cre recombinase activity in these locations, potentially in macrophages. In contrast, control (Cre-) mice show no detectable expression of tdTomato red fluorescence, indicating an absence of Cre recombinase expression.

4. Expression of Cre recombinase in the spleen

Figure 4. Immunofluorescence staining of spleen tissue. In Cre+ mice, a small amount of tdTomato protein signal is observed in the spleen, indicating low levels of Cre recombinase expression in this organ. In contrast, control (Cre-) mice show no detectable tdTomato signal, indicating an absence of Cre recombinase expression.

d. Summary

In the Cx3cr1-iCre mouse model, Cre recombinase expression is primarily localized in brain microglia. Cre recombinase-mediated recombination can also be detected in some parts of the intestine, lungs, liver, and skin, potentially in macrophages. Additionally, a small amount of recombination signal is observed in the spleen. In summary, this model exhibits a specific expression of Cre recombinase in brain microglia and macrophages in other tissues.

The Cre recombinase expression element integration site of this strain is located on chromosome 9, please avoid using flox mice with the transgenic locus on chromosome 9 for breeding.