An FRT flanked PGKneo cassette and a distal loxP site were inserted into intron 2 and a second loxP site was inserted about 1.1 kb upstream of the start site via homologous recombination. Cre mediated recombination removed exons 1 and 2. In situ hybridization analysis indicated absence of RNA expression in E10.5 homozygous embryos. RT-PCR analysis detected low levels of expression in homozygous mice. (J:163652)