A gene cassette composed of floxed mutant human RET gene cDNA with the 51(C618F) variant, an SV40 intron polyA followed by mCherry reporter gene and a neomycin resistance marker (Neo) that was flanked by FRT sites was inserted into the first coding exon of the mouse Ret gene. The neomycin resistance cassette was removed via FLP-mediated recombination in the germline. (J:275428)