The L1L2_Bact_P cassette was inserted at position 17722696 of Chromosome 16 upstream of the critical exon(s) (Build GRCm39). The cassette is composed of an FRT site followed by lacZ sequence and a loxP site. This first loxP site is followed by a neomycin resistance gene under the control of the human beta-actin promoter, SV40 polyA, a second FRT site and a second loxP site. A third loxP site is inserted downstream of the targeted exon(s) at position 17726149. The critical exon(s) is/are thus flanked by loxP sites.