These Msx2-creERT2 mutant mice carry a BAC derived transgene with tamoxifen inducible Cre recombinase under the control of the mouse Msx2 (msh homeobox 2) promoter/enhancer. When crossed with a strain containing a loxP site flanked sequence of interest, the offspring are useful for generating tamoxifen-induced, Cre-mediated targeted deletions. Tamoxifen administration induces Cre recombination in a pattern that recapitulate endogenous Msx2 expression pattern. Cre recombinase activity is detected in the apical ectodermal ridge of the limb bud and its underlying mesenchyme, and first pharyngeal arch mandibular process and cranial vault primordium at E11.5 after tamoxifen injection at E10.5. Tamoxifen pulse administration at E17.5 results in detection of Cre activity in the incisor dental papilla cells and whisker follicle cells, while treatment at postnatal day 1 results in detection of Cre activity at postnatal day 4 in the molar dental papilla.
Hemizygotes are viable and fertile. Homozygous viability/fertility has not been tested (July 2018). 
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 (17&beta;-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.

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This Msx2-creERT2 mutant mouse strain, carrying a transgene with tamoxifen-inducible Cre recombinase under the control of the mouse Msx2 (msh homeobox 2) promoter and enhancers, may be useful for generating targeted mutants specific to the apical ectodermal ridge (AER) and its underlying mesenchyme of the developing limb, and in studies of bone development and BMP signaling.

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