A floxed human RET cDNA with an SV40 intron and poly-adenyation site followed by CFP with a poly-adenylation site and an frt-flanked neo cassette were inserted into exon 1 removing 39 base pairs including the start methionine codon and codons for the first 6 amino acids of the signal peptide. Germ-line, flp-mediated recombination was used to remove the neo cassette and leave a floxed RET and a CFP cassette. (J:132854)