The transgene comprises the cDNA encoding the human ret proto-oncogene driven by the mouse metallothionein 1 promoter/enhancer and followed by a segment of the simian virus 40 (SV40) genome containing a splice signal, a polyadenylation signal and 3' flanking sequence. Northern blot analysis revealed low levels of transgene expression in hyperpigmented skin of non-albino mice of this line. (J:70622)