A loxP site was inserted into intron 1 and a second loxP site and an FRT site flanked neomycin resistance gene cassette into intron 5. The neo cassette was removed through subsequent flp-mediated recombination. Exons 2-5 were deleted through cre-mediated recombination by crossing these mice with mice carrying the Tg(rx3-icre)1Mjam allele. That allele shows leaky expression in the oocytes, thus creating some non-conditional null mouse lines i this crossing.