Vil1-MerCreMer Mice

The “Mouse Vil1 promoter-MerCreMer-rBG pA” gene expression element was inserted into the H11 locus in the genome of C57BL/6J mice.

a. Method

Vil1-MerCreMer mice were crossed with Rosa26-LSL-tdTomato mice to generate double heterozygous offspring. At 6 weeks of age, these offspring were subjected to Tamoxifen induction via intraperitoneal injection at a dose of 75 mg/kg for 5 consecutive days. This resulted in Cre recombinase-mediated deletion of LSL elements and subsequent expression of tdTomato in Cre-positive cells. One week after induction, tissues from the intestines, stomach, ureters, kidneys, ovaries, uterus, epididymis, and testes were collected from the offspring. The distribution of tdTomato was determined by immunofluorescence staining to assess the expression of Cre recombinase.

b. Groups

Cre+Tam+: Vil1-MerCreMer[KI/+];Rosa26-LSL-tdTomato[CKI/+], with Tamoxifen;
Cre+Tam-: Vil1-MerCreMer[KI/+];Rosa26-LSL-tdTomato[CKI/+], without Tamoxifen.

c. Result

(1) Expression of Cre recombinase in the small intestinal tissues

Figure 2. Immunofluorescence staining of duodenal, jejunal, and ileal tissues. The presence of abundant tdTomato-positive signals in the crypts and intestinal villus epithelial cells of the duodenum, jejunum, and ileum in Cre+Tam+ mice indicates strong expression of Cre recombinase in the small intestine. In contrast, no tdTomato expression or Cre recombinase activity was observed in these tissues in the non-tamoxifen-induced group.

(2) Expression of Cre recombinase in the large intestinal tissues

Figure 3. Immunofluorescence staining of the cecum, colon, and rectum tissues. The presence of abundant tdTomato-positive signals in the crypts and intestinal villus epithelial cells of the cecum, colon, and rectum in Cre+Tam+ mice indicates strong expression of Cre recombinase in the large intestine.

(3) Expression of Cre recombinase in the stomach, ureter, and kidney

Figure 4. Immunofluorescence staining of the gastric, ureteric, and renal tissues. The presence of a small amount of tdTomato-positive signal in kidney and stomach cells of Cre+Tam+ mice indicates trace expression of Cre recombinase. However, no such expression was observed in the ureter.

(4) Expression of Cre recombinase in the female gonads

Figure 5. Immunofluorescence staining of the uterus and ovary. The absence of tdTomato signals in the uterus and ovaries of Cre+Tam+ mice suggests that there is no Cre recombinase activity at these sites, and therefore no germline deletion of the target gene.

(5) Expression of Cre recombinase in the male gonads

Figure 6. Immunofluorescence staining of the testicular and epididymal tissues. The presence of only minimal amounts of tdTomato-positive signal in the testis and epididymis of Cre+Tam+ mice suggests that the likelihood of Cre recombinase expression leakage at these sites is extremely low, and therefore does not result in germline deletion of the target gene.

d. Summary

In Vil1-MerCreMer mice, the expression of Cre recombinase was primarily localized to the crypts and intestinal villus epithelial cells of both the large and small intestines. Only a small amount of Cre recombinase activity was detected in certain cells of the kidney and stomach, while no expression was observed in the ureters. Furthermore, Cre recombinase activity was virtually absent in the gonads, indicating a low likelihood of germline leakage. This model represents a highly tamoxifen-inducible, tissue-specific Cre mouse line targeting intestinal crypts and intestinal villus epithelial cells.

The transgenic element of this strain is located on chromosome 11, please avoid using flox mice with the transgenic locus on chromosome 11 for breeding.