The donating investigator reports variegated expression of the Lgr5-EGFP-IRES-CreERT2 transgene in the small intestine and colon (something which may happen often with genes that are expressed early during intestinal development). This variegated expression is advantageous for performing clonal lineage tracing and sorting intestinal stem cells, but may have limitations for more quantitative studies such as Lgr5-Cre driven knockout strategies.
While homozygous mice are not viable, heterozygous Lgr5-EGFP-IRES-CreERT2 mice are viable and fertile; harboring a Lgr5-EGFP-IRES-creERT2 "knock-in" allele that both abolishes Lgr5 (Gpr49) gene function and expresses EGFP and CreERT2 fusion protein from the Lgr5 promoter/enhancer elements. EGFP fluorescence is observed in crypt base columnar cells in small intestine (aka stem cells of the small intestine) and colon. Cre-ERT2 fusion gene activity is inducible; observed in the same cells only following tamoxifen administration. EGFP or inducible CreERT2 expression may also be observed in other Lgr5-expressing cell types (including pre-malignant mouse adenomas, colon cancer cells, epithelial stem cells of the stomach gland, basal epithelial layer stem cells of the mammary glands, and hair follicle stem cells).
The donating investigator reports variegated expression of the Lgr5-EGFP-IRES-CreERT2 transgene in the small intestine and colon (something which may happen often with genes that are expressed early during intestinal development). This variegated expression is advantageous for performing clonal lineage tracing and sorting intestinal stem cells, but may have limitations for more quantitative studies such as Lgr5-Cre driven knockout strategies.
The Cre-ERT2 fusion protein consists of Cre recombinase fused to a triple mutant form of the human estrogen receptor; which does not bind its natural ligand (17β-estradiol) at physiological concentrations but will bind the synthetic estrogen receptor ligands 4-hydroxytamoxifen (OHT or tamoxifen) and, with lesser sensitivity, ICI 182780. Restricted to the cytoplasm, Cre-ERT2 can only gain access to the nuclear compartment after exposure to tamoxifen. To counteract the mixed estrogen agonist effects of tamoxifen injections, which can result in late fetal abortions in pregnant mice, progesterone may be coadministered. As such, when Lgr5-EGFP-IRES-creERT2 mice are bred with mice containing loxP-flanked sequence of interest, tamoxifen-inducible, Cre-mediated recombination will result in deletion of the floxed sequences in the Lgr5-expressing cells of the offspring.
View cre expression characterization.
