The targeting construct introduced a loxP site upstream of exon 2 and an FRT-flanked puromycin resistance cassette with a 3 loxP site downstream of exon 2. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exon 2 floxed. Western blot analysis confirmed that both the alpha and beta isoform are no longer expressed. (J:312557)