Exon 10 was completely replaced with a PGK promoter and neomycin resistance gene cassette and a loxP site was inserted further downstream in intron 10. A correctly targeted ES cell line was further modified by the insertion of a loxP site flanked PGK promoter and hygromycin resistance gene cassette and an En-2 splice acceptor-IRES-LacZ expression cassette into exon 24. Removal of exon 10 causes a frame shift mutation, which disrupts the highly conserved formin homology domain SH2 and results in a protein product that includes out-of-frame translation after exon 9.