A neomycin selection cassette flanked by two loxP sites and a fragment including part of Jup introns 2-6 with a third loxP site inserted into intron 5 was engineered downstream of the neomycin selection cassette. The neomycin cassette was removed by breeding with Tg(EIIa-cre)C5379Lmgd mice, leaving exons 3-5 floxed