The L1L2_Bact_P cassette was inserted at position 39670138 of Chromosome 10 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 was 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 was inserted downstream of the targeted exon(s) at position 39671424 and subsequent Cre-mediated excision deleted the critical sequence and neomycin selection cassette yielding a reporter null allele. Further information on targeting strategies used for this and other IKMC alleles can be found at http://www.informatics.jax.org/mgihome/nomen/IKMC_schematics.shtml.