The L1L2_gtk cassette was inserted at position 80599973 of Chromosome 10 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 80600773. Exon 2 is thus flanked by loxP sites. A "conditional ready" (floxed) allele was created by flp recombinase expression in mice carrying this allele to remove the lacZ sequence and neo selection cassette, leaving exon 2 flanked by loxP sites.