STOCK Nkx2-1^{tm1.1(cre/ERT2)Zjh}/J

Stock number: 014552
Product name: Nkx2.1-CreER
Research areas: Cell Biology Research, Neurobiology Research, Research Tools

Description

The Nkx2.1-CreER (or Nkx2.1-CreERT2) knock-in/knock-out allele expresses a tamoxifen-inducible Cre recombinase from the endogenous promoter/enhancer elements of the NK2 homeobox 1 (Nkx2-1) gene. When induced, CreERT2 expression recapitulates endogenous Nkx2-1 expression, mainly in the medial and caudal ganglionic eminences of the basal ganglia and the preoptic area. These mice may be useful in studying the role of medial ganglionic eminences progenitor cells in GABAergic neuron development, as well as lung, thyroid, and pituitary development.

Detailed description

The Nkx2.1-CreER (or Nkx2.1-CreERT2) knock-in/knock-out allele was designed to both abolish NK2 homeobox 1 (Nkx2-1) gene function and expresses CreER^T2 fusion protein from the Nkx2-1 promoter/enhancer elements. Cre-ERT2 fusion gene activity is inducible; observed following tamoxifen administration. As such, when Nkx2.1-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 Nkx2-1-expressing cells of the offspring.

Heterozygous mice are viable, fertile, and normal in size with no gross physical or behavioral abnormalities reported by the donating investigator (although mice heterozygous from other null mutations of this gene exhibit impaired coordination and high thyroid-stimulating hormone levels). While the donating investigator reports the phenotype of homozygous mice as lethal, they may be expected to have defects similar to mice homozygous for other null mutations of this gene (including profound abnormalities of the ventral forebrain and lungs, a complete lack of thyroids, pituitary gland, and tracheo-esophageal septation, and perinatal death from respiratory failure).

Nkx2.1 mRNA or protein expression from the Nkx2.1-CreER mutant allele was not determined. The donating investigator reports tamoxifen-inducible Cre recombinase activity is specific and efficient; largely recapitulating the endogenous Nkx2-1 expression pattern, with highly efficient inducibility. Tamoxifen-inducible Cre recombinase activity was not tested prior to tamoxifen treatment. Following tamoxifen administration, Cre recombinase activity is observed in Nkx2.1 positive cells; including medial ganglionic eminence (MGE) progenitor cells and preoptic area. The donating investigators did not examine cre expression in tissues other than brain.

For characterization information, see images at the Allen Institute for Brain Science website (Nkx2-1-CreERT2 images).

If the recombinase activity pattern of this allele is further characterized by the Genetic Resource Science group at The Jackson Laboratory, such findings will be reported on the Mouse Genome Informatics (MGI) Allele Detail entry. This same information may also be found searching the MGI Recombinase Activity and MGI Gene Expression + Recombinase Activity Comparison Matrix.

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 NK2 homeobox 1 locus (Nkx2-1). This construct was electroporated into (C57BL/6 x 129S4Sv/Jae)-derived V6.5 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); see Stock No. 005703) to remove the neo selection cassette. These Nkx2.1-CreER (or Nkx2.1-CreERT2) mice were subsequently bred to C57BL/6 inbred mice for a few additional generations (and the FLPe transgene was removed). Next, Nkx2.1-CreERT2 mice were bred with Swiss Webster mice for several generations prior to sending to The Jackson Laboratory Repository. Upon arrival, mice were bred with C57BL/6J inbred mice (Stock No. 000664) for at least one generation to establish the Nkx2.1-CreERT2 colony.

Allele

Symbol: Nkx2-1^{tm1.1(cre/ERT2)Zjh}
Name: targeted mutation 1.1, Z Josh Huang
MGI accession ID: MGI:5302534
Generation method: Targeted
Attributes: Recombinase-expressing; Inducible
Marker symbol: Nkx2-1
Marker name: NK2 homeobox 1
Chromosome: 12
Strain of origin: (C57BL/6 x 129S4/SvJae)F1
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 Nkx2.1 positive cells; including medial ganglionic eminence progenitor cells and preoptic area of the brain.
Molecular note: A targeting vector was designed to insert a CreERT2 fusion gene , an SV40 polyA signal, and an frt-flanked neo cassette into the initiation codon of the NK2 homeobox 1 locus (Nkx2-1). This construct was electroporated into 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) to remove the neo selection cassette. These Nkx2.1-CreER (or Nkx2.1-CreERT2) mice were subsequently bred to C57BL/6 inbred mice for a few additional generations (and the FLPe transgene was removed).