A loxP site was inserted up stream of exon 2 and an FRT flanked neo/kan cassette and second loxP site were inserted downstream of exon 2 via homologous recombination. Recombinase mediated recombination removed the neo/kan cassette and exon 2. Immunofluorescence analysis confirmed the absence of expression at E10.5 in homozygous embryos. (J:164582)