The L1L2_gt0 cassette was inserted at position 29035613 of Chromosome 17 upstream of exon 5 (Build GRCm39). The cassette is composed of an FRT site flanked lacZ reporter/neomycin resistance gene cassette followed by a loxP site. An additional loxP site is inserted downstream of exon 7 at position 29037893. Exons are thus flanked by loxP sites. The reporter-selection cassette was removed through flp-mediated recombination, followed by the deletion of exons 5-7 through subsequent cre-mediated recombination. This leaves a null allele. (J:231042)