A targeting vector containing cDNA encoding icre fused to the mutated form of the ligand-binding domain of the human estrogen receptor followed by an Frt-flanked ampicillin resistance marker was generated. Homologous recombination resulted in the insertion of the vector into the start codon of the Adipoq locus present in a BAC clone (RP23-112M7; this BAC also contained the genes Kng1, Eif4a2, and Rfc4.) Flp-mediated excision removed the ampicillin marker. Five founders were obtained and crossed with lacZ reporter mice. Progeny of one founder displayed homogeneous lacZ expression in epididymal, mesenteric, and retroperitoneal white adipose tissue after tamoxifen treatment.