A loxP site was inserted in intron 1 and a loxP site and FRT flanked neo cassette were inserted in intron 3 via homologous recombination. Flp mediated recombination removed the neo cassette. Cre mediated recombination removed exons 2 and 3. Immunostaining and western blot analysis confirmed the absence of protein expression in retinas from homozygous mice.