Exons 2 - 4 were replaced with a nuclear localizing signal betagal coding sequence and a floxed pgk-neo cassette via homologous recombination. Cre mediated recombination removed the pgk-neo cassette. Western blot analysis of total kidney lysates from homozygous mice confirmed the absence of protein expression. LacZ expression is detected in the metanephros, ear, and nasal epithelium at E12.5 and in the developing bone at E13.5. (J:188593)