Pdx1-CreERT2 Mice

Catalog Number: C001537

Strain Name: C57BL/6JCya-Pdx1^{em1(Cre/ERT2)}/Cya

Genetic Background: C57BL/6JCya

Reproduction: Heterozygote x WT / Heterozygote x Heterozygote

Strain Description

Pancreatic and duodenal homeobox 1 (PDX1) is a transcription factor encoded by a gene regulating pancreatic development and β-cell-specific gene expression. It is also the first molecular marker during the differentiation and maturation of pancreatic stem cells. Activation of the PDX1 gene promotes insulin release and the expression of important genes in β-cells, making it a necessary condition for differentiating pancreatic stem cells into pancreatic β-cells. Additionally, various signaling molecules, such as glucagon-like peptide 1 (GLP-1) and cytokines, synergistically regulate the expression of the PDX1 gene. PDX1 is specifically expressed in early pancreatic epithelium and plays a role in proliferation and differentiation during development. In the adult stage, PDX1 is essential for hormone production in β-cells.

The Pdx1-CreERT2 mouse is constructed by inserting the “P2A-CreERT2” cassette upstream of the stop codon in the Pdx1 gene. Cre recombinase is expressed under the control of the Pdx1 gene regulatory elements. Without tamoxifen treatment, CreERT2 recombinase primarily resides in the cytoplasm. Only when tamoxifen is administered does the CreERT2 recombinase enter the cell nucleus and exert its recombination activity. When Pdx1-CreERT2 mice are crossed with mice containing loxP sites, tamoxifen induction can trigger sequence recombination between loxP sites mediated by Cre recombinase in the pancreatic cells of the offspring. It’s important to note that without tamoxifen treatment, there may be some leakage of CreERT2 recombinase expression before induction.

Strain Strategy

The “P2A-CreERT2” cassette was inserted upstream of the TGA stop codon.

Validation Data

a. Method

Pdx1-CreERT2 mice were crossed with ROSA26-LSL-tdTomato mice, which conditionally express a red fluorescent protein (tdTomato), to generate double-heterozygous offspring. When the offspring reached 8 weeks of age, they were intraperitoneally injected with a dose of 75 mg/kg tamoxifen for 4 consecutive days. Deletion of the stop element (LSL) mediated by Cre recombinase resulted in tdTomato protein expression in Cre-positive cells. One week after induction, pancreatic, duodenal, gastric, uterine, ovarian, lung, liver, brain, and thymus tissues were collected from the mice for immunofluorescence (IF) analysis to determine the expression of Cre recombinase.

b. Group

Cre+Tam+: Pdx1-CreERT2[KI/+]; Rosa26-LSL-tdTomato[CKI/+]; Tamoxifen;

Cre+Tam-: Pdx1-CreERT2[KI/+]; Rosa26-LSL-tdTomato[CKI/+]; Corn oil.

c. Result

1) Expression of Cre recombinase in the pancreas and duodenum

Figure 1. Immunofluorescence (IF) detection of tdTomato protein in the pancreas and duodenum. Histological examination revealed abundant tdTomato fluorescence signals in Cre+Tam+ mouse pancreatic islet cells. Additionally, red fluorescence was observed in non-islet cells and intestinal villi of the duodenum, indicating tdTomato expression mediated by Cre recombinase in these cells. Furthermore, even in Cre+Tam- mice that were treated with corn oil but not tamoxifen, a small amount of tdTomato leakage was detected in non-islet cells.

2) Expression of Cre recombinase in the stomach, uterus, ovaries, lungs and liver

Figure 2. Immunofluorescence (IF) detection of tdTomato protein in the stomach, uterus, ovaries, lungs, and liver. Histological examination revealed no significant red fluorescence signal in the stomach, uterus, ovaries, lungs, or liver of Cre+Tam+ mice, indicating that Cre recombinase-mediated tdTomato expression did not occur in these tissues. Similarly, in Cre+Tam- mice treated with corn oil but not tamoxifen, no fluorescence signal was detected in the corresponding tissues.

3) Expression of Cre recombinase in the thymus and brain

Figure 3. Immunofluorescence (IF) detection of tdTomato protein in the thymus and brain. Histological examination revealed minimal red fluorescence signals in the thymus of Cre+Tam+ mice, indicating tdTomato expression mediated by Cre recombinase in this tissue. However, no significant red fluorescence was observed in brain tissue, suggesting that Cre recombination did not occur in the brain. In Cre+Tam- mice treated with corn oil but not tamoxifen, no fluorescence signal was detected in the corresponding brain tissues.

d. Summary

In the Pdx1-CreERT2 mouse model, Cre recombinase is significantly expressed in the pancreas, and minimal recombination signals are observed in the duodenum and thymus. However, no apparent recombination signals are detected in the stomach, uterus, ovaries, lungs, liver, or brain tissues. These findings indicate good tissue specificity for this model. Overall, this model can be used for targeted research on pancreatic islet cell tissue specificity.

Announcements

The insertion site of the Cre recombinase gene expression cassette in this strain is located on chromosome 5. Please avoid breeding with gene-edited mice targeting genes on the same chromosome as the Cre mouse when conducting mating.