The L1L2_Bact_P cassette was inserted at position 55628889 of Chromosome 13 upstream of exon 1 (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 cassette 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 6 at position 55631060. The critical exons are thus flanked by loxP sites. This reporter knockout allele was created through subsequent cre-mediated recombination, deleting exons 1-6 and keeping the lacZ and neo cassettes in place. (J:148605, J:173534, J:188991)