A loxP site was inserted upstream of the coding sequence. A lacZ gene with a 5' loxP site was inserted downstream of the coding sequence. Flp-mediated recombination removed the FRT-flanked neomycin resistance cassette inserted downstream of the second loxP site. Western blot analysis confirmed reduced protein expression in the brain and heart. This allele is hypomorphic. Reporter expression requires cre-mediated removal of the coding sequence.