LoxP sites and an frt-flanked neomycin resistance cassette were inserted flanking the first coding exon. A tau-LacZ gene was also inserted 3' to the neomycin resistance gene. A null allele was generated by crossing the loxP-flanked allele to beta-actin-Cre expressing mice, an allele with germline Cre expression, and subsequently crossing out the Cre transgene by backcrossing to ICR. (J:73071, J:135134)