A targeting vector was designed to insert a CreERT2 fusion gene (Cre-ERT2; 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 Lhx6 (LIM homeobox protein 6) gene. Mutant mice were bred with Actin-FLPe mice (on a C57BL/6 congenic background) to remove the neo selection cassette. These Lhx6-CreERT2 mice were subsequently bred with wildtype siblings and/or wildtype C57BL/6 mice for at least one generation (and the FLPe transgene was removed)