The gene was disrupted by insertion of an EGFP-derived cassette and a floxed neo cassette into exon 1 via homologous recombination. The floxed neo cassette was removed by mating mutant animals to cre deleter strain TgN(ACTB-cre)2Mrt. Immunohistochemical analysis of homozygous mutant newborns confirmed the absence of gene expression in spinal motorneurons. (J:71881)