The L1L2_gt0 cassette was inserted at position 79280528 of Chromosome 11 upstream of the critical exon 4 (Build GRCm39). The cassette is composed of an FRT flanked lacZ/neomycin sequence followed by a loxP site. An additional loxP site is inserted downstream of the targeted exon at position 79281558. The critical exon 4 is thus flanked by loxP sites. A "conditional ready" (floxed) allele is created by flp recombinase expression in mice carrying this allele. The knockout allele was created by deletion exon 4 through subsequent cre-mediated recombination.