A loxP site was inserted into the transcription start site of Klhl1, which is also the upstream region of the polyA signal of Klhl1as. A neo cassette flanked with 2 FRT sites and a 3' loxP site were inserted into the first intron of Klhl1, which is downstream of the transcription start site of Klhl1as. Crossing with mice that express FLP in the germline resulted in the removal of the neo, leaving exon 1 of Klhl1 flanked by loxP sites and the complete coding sequence for Klhl1as flanked by loxP sites.