A targeting vector containing an FRT-flanked PGK-Neo selection cassette followed by a loxP site inserted upstream of exon 3 and another loxP site was inserted downstream of exon 10. Flp-mediated recombination removed the FRT-flanked neo cassette leaving exons 3 through 10 floxed. Germ line, cre mediated recombination removed exons 3-10, which contain the first and largest extracellular loop of the protein. Immunoprecipitation of lung and kidney tissues confirmed that no protein was expressed in mutant mice.