A STOP cassette (triple polyadenylation signal sequences) was inserted into exon 1, truncating Dlx6os1 splice variant Evf2 from 3.7 kb to 101 bp without affecting the transcription of splice variant Evf1. RT-PCR confirmed that the expression of Dlx5 and Dlx6 are increased. A loxP site flanked neomycin resistance gene cassette was removed by cre-mediated recombination.