cDNA encoding cre recombinase fused to the mutated human estrogen receptor ligand-binding domain (ERT2) and followed by a polyadenylation signal and an Frt-flanked neo cassette was inserted into the start codon of the mouse Bmx gene located in the P1 artificial chromosome (PAC; RPCI21) using recombineering methods. Flp-mediated excision in bacteria removed the neo marker. The validated construct was injected into fertilized oocytes to generate founders (details not available). Founders were bred to reporter mice to assess recombination efficiency and specificity; mice display inducible artery-specific cre activity.