LoxP sites and an frt-flanked neomycin selection cassette were inserted to flank the coding exon. The coding exon and neomycin selection cassette were deleted via Cre-mediated recombination in the germline. RT-PCR analysis of brain lysates confirmed the absence of mRNA expression in the brain of homozygous mutant mice while moderate to high expression was observed in heterozygous and wild-type mice, respectively. (J:301765)