The L1L2_gt0 cassette was inserted at position 124713564 of Chromosome 4 upstream of the critical exon(s) (Build GRCm39). The cassette is composed of an FRT flanked lacZ/neomycin sequence followed by a loxP site. An additional loxP site was inserted downstream of the targeted exon(s) at position 124714524. The critical exon(s) were thus flanked by loxP sites, and subsequent Cre-mediated excision deleted the critical sequence and the neomycin selection cassette yielding a reporter knockout 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.