A loxP site was inserted usptream of the fourth coding exon (exon 3 in publication's gene model). An FRT-flanked neomycin resistance cassette with a 3' loxP site was inserted downstream of the same exon. Flp-mediated recombination removed the neomycin resistance cassette and left the exon floxed. Cre-mediated recombination removed the exon.