The targeting vector contains a FRT-flanked Neo selection cassette and a loxP site was inserted downstream of the first protein coding exon of the targeted gene, and another loxP site was inserted upstream of the first protein coding exon. Flp-mediated recombination removed the FRT-flanked neo cassette. Cre-mediated recombination removed the first protein coding exon. Western blot and immunohistochemical analysis of spinal cord confirmed the absence of protein expression.