An EGFP reporter followed by poly(A) signal and a loxP-flanked neomycin selection cassette were inserted into the initiation codon within exon 1 of the gene. The floxed selection cassette in the vector was excised by Cre-mediated recombination by transient transfection with a Cre-expressing plasmid in targeted ES cells. The embryos showed a typical vascular pattern of expression. Real-time PCR analysis of hearts isolated from 5 days old mice showed that the expression of the gene in heterozygous mice was reduced to about 50% of wild-type levels.