Amplified DNA in cells of genetic melanoma of Xiphophorus.

Melanomas of genetic origin develop in interspecies hybrids of the fish Xiphophorus. Cytogenetic analyses have indicated chromosomal manifestations of amplified DNA in cells of an in vitro established cell line derived from a melanoma. We have employed strategies of differential hybridization in agarose gels to isolate and clone a portion of the amplified DNA. Amplification was about 20-fold in melanoma cells established in culture and about 10-fold in 2 out of 5 melanomas directly derived from the animal. The amplified DNA contained at least one transcription unit that is evolutionarily conserved in all vertebrates tested, including chicken, murines and man. Our results indicate that amplification of an as yet uncharacterized gene is involved in genetic melanoma of Xiphophorus.