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. Immunohistochemistry indicates that both the full-length and shorter splicing variant (variant 1 with transcriptional start site in exon 7) proteins are almost completely eliminated in the brain of homozygotes. (J:243531)