Study of spontaneous oncogenesis in selected fish species, the brown bullhead (Ameiurus nebulosus) and the walleye (Stizostedion vitreum), and of the molecular mechanisms of pathogenesis of walleye dermal sarcoma virus (WDSV) in walleye

The orocutaneous neoplasm of brown bullhead and the dermal sarcoma of walleye are common spontaneous neoplastic conditions. Brown bullhead orocutaneous neoplasms arise from the Malpighian epithelial cell of the cutaneous and/or oral epithelium. Benign papillomas can apparently progress into invasive carcinomas. These neoplasms could not be reproduced in test brown bullheads by inoculation of tumor tissue homogenate or live cells. Reverse transcriptase activity was detected in the tumors. No sequence homologous to papillomavirus or WDSV sequences could be identified by southern blotting of genomic DNA from tumor tissue. Ultrastructurally, the neoplastic cells showed three major alterations. These were loss of zonal distribution of organelles, disorganization of bundles of intermediate filaments and well-developed vesicular system.; Individual dermal sarcomas of walleyes were studied by in situ hybridization and immunohistochemistry for the presence of WDSV nucleic acids and antigen, presumably envelope. Abundant viral transcripts were detected in the neoplastic cells. Viral DNA was found in the neoplastic cells, mononuclear inflammatory and epidermal cells. Neoplastic cells containing the viral protein were less numerous than those expressing viral transcripts. This experiment associated dermal sarcomas of walleyes with high transcriptional activity of WDSV.; WDSV infection and transcriptional activity were studied in the organs of 3 tumor-bearing and 3 grossly unaffected walleyes. WDSV DNA and RNA sequences were detected by PCR and RT-PCR. The presence of WDSV DNA in the sperm genomic DNA from 10 unrelated walleyes was also investigated. Viral DNA was present in the organs of tumor-bearing and unaffected walleyes and in three sperm samples. Low levels of WDSV RNA were detected in the spleen and kidney of unaffected walleyes. In contrast, WDSV RNA was found in almost all the organs of tumor-bearing walleyes. RNA/DNA ratio indicated that tumor-bearing walleyes harbored transcriptionally active WDSV, while WDSV remained mostly silent in unaffected walleyes.