A construct with the following elements (5' to 3") was inserted into intron 1: loxP site, EGFP, FRT site, puro cassette, loxP site, mouse Pax8 cDNA (Genbank accession number: BF781092), IRES, nuclear localized lacZ, FRT fite, and a polyadenylation sequence. Expression of Pax3 is replaced with expression of Pax8.