A loxP site was inserted into intron 1 and an FRT site flanked neomycin reistance gene cassette with a 5' loxP site was inserted into intron 2. Flp-mediated recombination removed the neo cassette. Exon 2 was removed by cre-mediated recombination. The absence of protein expression was confirmed by immunohistochemistry on uterine sections.