A loxP site was inserted upstream of exon 8 and a loxP site and a FRT-flanked neomycin cassette were inserted downstream of exon 8 in opposite orientation. Cre-mediated recombination removed exon 8 and the selection cassette in germline. The full-length protein is completely eliminated in homozygous brain, however expression of a short isoform (variant 2 with transcriptional start site in exon 9) is increased. (J:243531)