In situ Hybridization and Immunohistochemical Study of Walleye Dermal Sarcoma Virus (WDSV) Nucleic Acids and Proteins in Spontaneous Sarcomas of Adult Walleyes (Stizostedion vitreum)

Abstract

Twenty-two anatomically independent dermal sarcomas from six adult walleye fish (Stizostedion vitreum) collected during the spring from Oneida Lake, New York, were examined by in situ hybridization and immunohistochemistry for the presence of walleye dermal sarcoma virus (WDSV). The viral RNA, DNA, and 90-kd protein were localized at the cellular level. Riboprobes complementary to the 5' terminal region of WDSV genome were used to detect viral nucleic acids. Rabbit polyclonal antiserum was generated against the 90-kd virus-associated antigen, presumably a product of the env gene, for immunohistochemical studies. Viral transcripts were detected in the neoplastic cells of all dermal sarcomas, in which they were generally abundant. Rare mononuclear inflammatory cells and cells within the epidermis also expressed viral RNA. In all sarcomas, low to moderate levels of viral DNA were present in all neoplastic and most mononuclear inflammatory and epidermal cells. Many neoplastic cells were immunopositive for the virus-associated protein. The distribution of immunopositive neoplastic cells mimicked approximately that of cells containing viral transcripts. The number of neoplastic cells with transcripts exceeded that of cells with protein, suggesting that productively infected neoplastic cells constituted a subset of the neoplastic cells that expressed WDSV transcripts. The viral antigen was also present within many mononuclear inflammatory cells. These data suggested that 1) dermal sarcomas were associated with elevated transcriptional activity of WDSV in the neoplastic cells and 2) the cell tropism of WDSV extended beyond the mesenchymal fibroblast-like neoplastic cells and included at least mononuclear inflammatory and epidermal cells.