The targeting construct was designed to replace exons 29-34 (encoding the intracellular domain) with a CreERT2 sequence and nuclear localization signal, followed immediately downstream by a C-terminal 6xMyc epitope tag, 2xSV40 polyadenylation sequence, and frt-flanked Pgk1/EM7 promoter-driven neomycin selection cassette. The CreER fusion gene (Cre-ERT2) is Cre recombinase fused to a G400V/M543A/L544A triple mutation of the human estrogen receptor ligand binding domain. (J:172930)