STOCK Wt1^{tm2(cre/ERT2)Wtp}/J

Stock number: 010912
Product name: Wt1^CreERT2
Research areas: Cardiovascular Research, Developmental Biology Research, Internal/Organ Research, Reproductive Biology Research, Research Tools

Description

The Wt1^CreERT2 knock-in allele in these mice both abolishes Wilms tumor 1 homolog gene function and directs expression of the CreERT2 fusion protein to proepicardium and epicardium by the Wt1 promoter/enhancer elements. As Wt1 is expressed in the developing genitourinary system and in the mesothelia overlying most visceral organs, these mutant mice are useful as a tamoxifen-inducible Cre-lox tool for lineage-tracing/marking Wt1-expressing cells for studying cardiomyocytes in the developing heart.

Detailed description

Homozygous mice die between embryonic day (E)13.5 and birth with defects of heart, kidney, gonads, and multiple other organs. Heterozygous (Wt1^CreERT2/+) mice are viable and fertile. The Wt1^CreERT2 "knock-in" allele both abolishes Wt1 gene function and has expression of the CreER^T2 fusion protein (CreERT2) under control of the Wt1 promoter/enhancer elements. In heart from heterozygous mice, CreERT2 expression is directed to proepicardium and epicardium from E9.5 to E15.5, and is not found in the myocardium. CreERT2 fusion gene activity is inducible; observed following tamoxifen administration. As such, when Wt1^CreERT2 mice are bred with mice containing loxP-flanked sequence, tamoxifen-inducible Cre-mediated recombination will result in deletion of the floxed sequences in the Wt1-expressing cells of the offspring. The donating investigator reports that Cre activity may be observed prior to tamoxifen exposure only in epicardium of adult mice following myocardial infarction. As Wt1 is expressed in the developing genitourinary system and in the mesothelia overlying most visceral organs, these mutant mice are useful as a tamoxifen-inducible Cre-lox tool for lineage-tracing/marking Wt1-expressing cells for studying cardiomyocytes in the developing heart.

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.

Development

A targeting vector was designed to replace exon 1 of the Wt1 (Wilms tumor 1 homolog) locus with a CreER^T2 fusion gene (Cre-ER^T2; Cre recombinase fused to a G400V/M543A/L544A triple mutation of the human estrogen receptor ligand binding domain), an SV40 polyA signal, and an frt-flanked pgk-Neo cassette. The donating investigator reports that this construct was electroporated into 129S4/SvJae-derived J1 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts and chimeric mice were bred with outbred Swiss Webster (CFW) mice to originate the colony. To remove the pgk-Neo cassette, mutant mice were bred with Actin-FLPe mice (mostly C57BL/6 genetic background; see Stock No. 005703). The resulting Wt1^CreERT2 mice were subsequently mated with outbred Swiss Webster (CFW) mice for several generations (and the FLPe transgene was removed) prior to sending to The Jackson Laboratory Repository. Upon arrival, mice were bred with B6129SF1/J hybrid mice (Stock No. 101043) for at least one generation to establish the Wt1^CreERT2 colony.

Allele

Symbol: Wt1^{tm2(cre/ERT2)Wtp}
Name: targeted mutation 2, William T Pu
MGI accession ID: MGI:3801682
Generation method: Targeted
Attributes: Recombinase-expressing; Inducible
Marker symbol: Wt1
Marker name: Wilms tumor 1 homolog
Chromosome: 2
Strain of origin: 129S4/SvJae
Expressed genes: cre/ERT2,Cre recombinase and estrogen receptor 1 (human) fusion gene,
Site of expression: Cre activity is observed prior to tamoxifen exposure only in epicardium of adult mice following myocardial infarction.
Molecular note: Exon 1 was replaced with an inducible cre ESR1 (ERT2) fusion followed by an frt-flanked neo cassette. Germ line, flp-mediated recombination was used to remove the neo cassette.