Oncogenes in hematopoietic and hepatic fish neoplasms

Neoplastic transformation of cells has often been associated with changes in cellular oncogenes. While much information has been collected in mammalian systems, relatively little is known about the molecular basis of tumor progression in lower vertebrates. For our studies, tumors were collected from feral northern pike (Esox lucius) from Ostego Lake, MI, where the local population exhibited a 15% incidence of large external lymphomas. In laboratory studies, tumors were induced under controlled conditions by known mammalian carcinogens in the Japanese medaka (Oryzias latipes), a small aquarium fish widely used in carcinogenicity studies. DNA isolated from these tumors was assayed for transforming sequences by transfection into NIH3T3 cells. DNAs from the northern pike lymphomas and the chemically induced tumors in the medaka were able to transform NIH3T3 cells and induce tumors in athymic mice. The results of our studies to date are summarized here, together with the current status of oncogene activation in other fish systems.