The L1L2_gt2 cassette was inserted at position 179250641 of Chromosome 1 upstream of the critical exon 2 (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 exon 2 at position 179251462. The critical exon(s) is/are thus flanked by loxP sites. A null/knockout allele was created by flp and cre recombinase expression in mice carrying this allele to remove the lacZ sequence, neo selection cassette and the loxP-flanked exon 2. (J:240508)