The targeting construct inserted a loxP site and FRT-flanked neomycin resistance cassette upstream of exon 2 and inserted an F3 flanked puromycin resistance cassette and loxP site downstream of exon 3. Flp-mediated recombination removed both selection cassettes and left exons 2 and 3 floxed. Cre-mediated recombination removed exons 2 and 3. (J:298763)