The L1L2_Bact_P cassette was inserted at position 55174959 of Chromosome 14 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 55176866. The critical exon(s) is/are thus flanked by loxP sites. Flp-mediated recombination removed the lacZ and neomycin resistance gene. Cre-mediated recombination in the germline deleted the floxed exon(s).