The L1L2_gt2 cassette was inserted at position 31887866 of Chromosome 5 upstream of the critical exon 3 (Build GRCm39). The cassette is composed of an FRT flanked lacZ/neomycin sequence followed by a loxP site. An additional loxP site is inserted downstream of the targeted exon 3 at position 31888629. The critical exon 3 is thus flanked by loxP sites. Cre expression without flp expression creates a reporter knockout mouse. 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. Western blot analysis and immunofluorescence confirmed the absence of protein expression in fibroblasts.