The Gad2-CreERT2 knock-in/knock-out allele both abolishes Gad2 gene function and expresses a CreER^T2 fusion protein (creERT2 fusion protein) from the Gad2 promoter/enhancer elements. Heterozygous mice are viable and fertile with no reported abnormalities. Homozygous mice are expected to have a knockout phenotype similar to other null mutations of this gene and may exhibit increased seizure activity (although no early death is reported). Cre-ERT2 fusion gene activity is inducible; observed following tamoxifen administration. As such, when Gad2-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 Gad2-expressing cells of the offspring.

The donating investigator reports tamoxifen-inducible Cre recombinase activity is specific and efficient (largely recapitulates the endogenous Gad2 expression pattern with highly efficient inducibility). They report tamoxifen-inducible Cre recombinase activity is observed in the cortex and cerebellum, as well as very rare incidence of Cre activity in the cortex prior to tamoxifen administration.

For characterization information, see images at the Allen Institute for Brain Science website (Gad2-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.