STOCK Cck^{tm2.1(cre/ERT2)Zjh}/J

Stock number: 012710
Research areas: Neurobiology Research, Research Tools

Description

The Cck-CreER (or Cck-CreERT2) knock-in allele both abolishes cholecystokinin (Cck) gene function and expresses the CreER^T2 fusion protein in cholecystokinin positive cortical neurons (both interneurons and pyramidal neurons) as directed by the endogenous Cck promoter/enhancer elements. Cre-ERT2 fusion gene activity is inducible by the administration of tamoxifen.

Detailed description

The Cck-CreER (or Cck-CreERT2) knock-in allele both abolishes cholecystokinin (Cck) gene function and expresses the CreER^T2 fusion protein from the Cck promoter/enhancer elements. The donating investigator reports that homozygous mice are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Homozygotes may be expected to have a phenotype similar to other null mutations of this gene and may exhibit metabolic abnormalities of the endocrine/exocrine glands (increased pancreatic amylase).

Cre-ERT2 fusion gene activity is inducible; observed following tamoxifen administration. As such, when Cck-CreERT2 mice are bred with mice containing loxP-flanked sequences, tamoxifen-inducible Cre-mediated recombination will result in deletion of the floxed sequences in the Cck-expressing cells of the offspring. These Cck-CreERT2 mice may be useful in studying brain anatomy, physiology and behavior.

The donating investigator reports tamoxifen-inducible Cre recombinase activity recapitulates the endogenous Cck expression pattern, with moderate efficiency of induction. They report tamoxifen-inducible Cre recombinase activity is not observed prior to tamoxifen treatment. Following tamoxifen administration, Cre recombinase activity is observed in cholecystokinin positive neurons in cortex (both interneurons and pyramidal neurons). The donating investigators did not examine cre expression in subcortical neurons or in any tissues other than brain.

For characterization information, see images at the Allen Institute for Brain Science website (Cck-CreERT2 images).

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 insert 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 neo cassette into the initiation codon of the cholecystokinin locus (Cck). This construct was electroporated into C57BL/6-derived Bruce4 embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts.

Chimeric males were bred with albino C57BL/6 females (Tyr^c-2J ; see Stock No. 000058), and black pups harboring the cre targeted mutation were selected. Mutant mice were then bred with Actin-FLPe mice (on a C57BL/6 congenic background (N10); see Stock No. 005703) to remove the neo selection cassette. The donating investigator reported that Cck-CreER (or Cck-CreERT2) mice were subsequently bred to C57BL/6 inbred mice for two additional generations and then bred together for many more generations (and the FLPe transgene was removed) prior to arrival at The Jackson Laboratory Repository (see SNP note below). Upon arrival, mice were bred with C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the Cck-CreER colony. These Cck-CreER mice may still be segregating at the Tyr locus.

A 32 SNP (single nucleotide polymorphism) panel analysis, with 27 markers covering all 19 chromosomes and the X chromosome, was performed on the first generation rederived living colony at The Jackson Laboratory Repository. This revealed 10 of 27 markers (one each on chromosomes 1, 6, 8, 9, 11, 12, 15, and 19, and two markers on chromosome 17) that were not fixed for C57BL/6 allele-type (e.g.: still segregating for allele-type markers of other genetic backgrounds). These data suggest the mice were not backcrossed to C57BL/6 prior to arrival at The Jackson Laboratory, and the colony is a mix of one or more different genetic backgrounds other than C57BL/6.

Allele

Symbol: Cck^{tm2.1(cre/ERT2)Zjh}
Name: targeted mutation 2.1, Z Josh Huang
MGI accession ID: MGI:5014094
Generation method: Targeted
Attributes: Recombinase-expressing; Inducible
Marker symbol: Cck
Marker name: cholecystokinin
Chromosome: 9
Strain of origin: C57BL/6
Expressed genes: cre/ERT2,Cre recombinase and estrogen receptor 1 (human) fusion gene,
Site of expression: Following tamoxifen administration, Cre recombinase activity is observed in cholecystokinin positive neurons in cortex (both interneurons and pyramidal neurons).
Molecular note: A targeting vector was designed to insert a CreERT2 fusion gene (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 neo cassette into the initiation codon of the cholecystokinin locus (Cck). This construct was electroporated into C57BL/6-derived embryonic stem (ES) cells. Correctly targeted ES cells were injected into recipient blastocysts and chimeric mice were bred with C57BL/6 mice to originate the colony. Mutant mice were bred with Actin-FLPe mice (on a C57BL/6 congenic background (N10)) to remove the neo selection cassette. These Cck-CreER (or Cck-CreERT2) mice were subsequently bred to C57BL/6 inbred mice for two additional generations and then bred together for many more generations (and the FLPe transgene was removed).