Exons 2 and 3 were replaced with a lacZ reporter, loxP site, self-deleting protamine promoter, cre recombinase, neomycin selection cassette and second loxP site using Regeneronâs VelociGene technology. The neomycin selection marker located between two loxP sites was deleted with cre recombinase under self-deleting protamine promoter, leaving beta-galactosidase gene (LacZ) and one loxP site in the flanking intron. Western blot analysis confirmed the absence of protein in liver lysates.