The L1L2_Bact_P cassette was inserted at position 9984471 of Chromosome 1 upstream of exon 5 (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 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 exon 7 at position 9987378. Exons 5-7 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 exons 5-7.