The endogenous myosin, heavy polypeptide 9, non-muscle (Myh9) gene was modified by a codon substitution (GAC>AAT) in exon 31 that replaces aspartic acid with asparagine at amino acid position 1424, in the rod region of the protein (D1424N), and by insertion of a loxP flanked PGK-neomycin resistance cassette into the following intron. (J:175367)