Exon 2, which contains the entire coding region, was replaced by a cassette containing an enhanced GFP-LacZ fusion gene and a floxed PGK-neo gene. In situ hybridization of brain sections showed a lack of transcript in the Edinger-Westphal (EW) nuclei of homozygous mutant mice. Correlatively, expression of beta-galactosidase was observed in the EW nuclei of mutant mice. (J:78595)