The open reading frame of the Cre recombinase gene, followed by the human growth hormone polyadenylation signal and the neomycin resistance gene, has replaced all except the 5'-most segment of the first exon, the first intron and all but the 3'-most part of the second exon of the myelin oligodendrocyte glycoprotein gene, thus targeting Cre expression to oligodendrocytes (ODCs). Western blot analysis demonstrated that wild-type MOG protein is present in heterozygous and wild-type brains at comparable levels, but is not detectable in homozygous mutant brain. (J:114741)