Catalog Number: C001537
Strain Name: C57BL/6JCya-Pdx1em1(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.
4) Expression of Cre recombinase in the pancreas
Figure 4. Spontaneous fluorescence in pancreatic tissue. Based on histological analysis, the results reveal orange spontaneous fluorescence signals in the islet cells, acinar cells, and ducts of Cre+Tam+ mice. The recombination efficiency in the 150 mg/kg Tamoxifen-treated group is higher than in the 75 mg/kg Tamoxifen-treated group. Additionally, a small amount of tdTomato leakage is detected in the pancreas of Cre+Tam- mice that were treated with corn oil but not tamoxifen.
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. Overall, this model exhibits good specificity for targeting pancreatic islet cells. We recommend using a continuous induction of 150 mg/kg Tamoxifen for 4 days, with optimal effects observed 7 days after induction.
Announcements
The CreERT2 recombinase gene expression cassette is integrated into chromosome 5 in this strain. it is recommended to avoid breeding with Flox mice that have been targeted on the same chromosome.