A floxed neomycin resistance cassette replaced exons 1a and 1b. Cre-mediated recombination removed the selection cassette. The translation start codon, AUG, in exon 2 was replaced UAA to created an aberrant splice acceptor site. Another round of cre-mediated recombination removed the neomycin resistance cassette inserted into intron 2. (J:245723)