This transgene uses the cytochrome P450, family 19, subfamily a, polypeptide 1 promoter to drive expression of cre recombinase in the placenta. The transgene also contains an IRES-luciferase, the rabbit beta-globin intron and the SV-40 polyA signal. X-gal staining revealed that cre was expressed strongly in the skin and lens as well as the trilaminate layers of the placenta. Almost a third of the fetuses (29%) expressed cre throughout internal organs, including the heart, liver and brain. (J:121714)