A 3 nucleotide (AAG) deletion that removes lysine 32 was introduced into exon 1 and a floxed neo-cre cassette was inserted into intron 1 via homologous recombination. The neo-cre cassette is self-excising in the male germ line. In homozygous mice protein expression of lamin A/C is reduced in skeletal muscles and it fails to relocalize to the nuclear periphery in developing embryos at E17.5. (J:180603)