An FRT-flanked neomycin resistance cassette with a 5' loxP site was inserted upstream of exon 6. An additional loxP site was inserted downstream of exon 6. Flp-mediated recombination removed the selection cassette. Cre-mediated recombination removed exon 6. Western blot analysis confirmed the absence of isoform alpha 2 but continued expression of isoform alpha 1 in the hippocampus. (J:229380)