The L1L2_gt1 cassette was inserted at position 141361279 of Chromosome 4 upstream of the critical exon(s) (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(s) at position 141362264. The critical exon(s) is/are thus flanked by loxP sites. A null/knockout allele was created by cre recombinase expression in mice carrying the tm1a allele to remove the neo selection cassette and loxP-flanked critical exon(s). (J:256313)