Mice hemizygous for the transgenic insert are viable, fertile, normal in size and do not display any gross physical or behavioral abnormalities. Homozygotes are not viable. These transgenic mice express the Cre recombinase under the control of the mouse homeobox B7 enhancer and promoter. Recombination closely patterns the endogenous gene expression. Cre recombinase expression is detected in the mesonephric duct as early as embryonic day 9.5, in the ureteric bud by embryonic day 10.25 and in all ureteric bud epithelial cells by embryonic day 12.5. Low levels of expression are detected in the dorsal root ganglia and the spinal cord. When crossed with a strain containing a loxP site flanked sequence of interest, Cre-mediated recombination results in deletion of the flanked sequence in the mesonephric duct and its developmental derivatives (the Wolffian duct, the collecting duct epithelium of kidney and ureteral epithelium). This strain represents an effective tool for generating tissue-specific targeted mutants that would be useful in examining developmentally critical gene function in renal system development. The Jackson Laboratory 2024, used with permission.