A loxP-flanked neomycin resistance (neo) cassette was inserted into intron 3 and a third loxP site into intron 10. The neo cassette was deleted by Cre recombinase in vivo, leaving a single loxP site in intron 3. Crossing mice with this allele to animals expressing Cre recombinase will result in deletion of exons 4-10, inactivating the gene, in the offpring in the tissues or cell types where Cre is expressed.