A loxP site was inserted upstream of exon 4 and an FRT flanked neo cassette and second loxP site were inserted downstream of exon 9 via homologous recombination. Flp mediated recombination removed the neo cassette. Cre mediated recombination removed exons 4 - 9. Quantitative PCR and immunoblot analysis confirmed the absence of mRNA and protein expression in homozygous mice.