The L1L2_gt0 cassette was inserted at position 72610840 of Chromosome 6 upstream of the critical exon(s) (Build GRCm39). The cassette is composed of an FRT flanked lacZ reporter/neomycin resistance fusion gene followed by a loxP site. An additional loxP site is inserted downstream of the targeted exon(s) at position 72611703. The critical exon(s) is/are thus flanked by loxP sites. A "conditional ready" (floxed) allele was created through subsequent flp recombinase expression in mice carrying this allele. (J:235736, J:262044)