A loxP site was inserted in intron 5 and an FRT flanked neo cassette and loxP site were inserted in intron 8 via homologous recombination. Flp mediated recombination removed the neo cassette. Cre mediated recombination removed exons 6 - 8. Western blot analysis confirmed the absence of protein expression in yolk sac derived endothelial cells. (J:185401)