A targeting vector was designed to insert a CreERT2 fusion gene, an SV40 polyA signal, and anFRT-flanked neo cassette into the initiation codon of the Calb2 (calbindin 2; also called calretinin or CR) locus. This construct was electroporated into C57BL/6-derived embryonic stem (ES) cells. Mutant mice were bred with Actin-FLPe mice to remove the neo cassette, (J:151755)