Mice hemizygous for this Adipoq-CreERT2 BAC transgene are viable and fertile, with expression of a tamoxifen inducible Cre recombinase (cre/ERT2) directed to adipose tissue by the promoter/regulatory regions of the mouse adiponectin (Adipoq) locus on the BAC transgene. When crossed with a Rosa26LacZ reporter tamoxifen induced Cre recombination is detected in 97%–99% of adipocytes in white adipose tissue and approximately 15% of adipocytes in brown adipose tissue. No tamoxifen induced Cre recombination is detected in liver, pancreas, gut, kidney, lung, aorta, skeletal muscle, heart, spleen, thymus, cerebrum, or cerebellum. Cre recombinase activity is not detected in the absence of tamoxifen.
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.
