A neomycin resistance cassette replaced 1.4kb of the gene, including part of the promoter through part of the second intron. Northern blot analysis using a mouse exon 4 riboprobe did not detect wild-type message in livers from homozygous mutant mice, but did detect a longer transcript that the authors propose is a neo-Apoe fusion product. Gradient SDS-PAGE analysis did not detect full size Apoe associated with any fractions from plasma lipoproteins from homozygous mutant mice.