The L1L2_gt2 cassette was inserted at position 98816214 of Chromosome 4 upstream of the critical exon 3 (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 3 at position 98816874. The critical exon 3 is thus flanked by loxP sites. Flp- and cre-mediated recombination removed the reporter cassette and exon 3.