Nucleotide sequence and protein analysis of a complex piscine retrovirus, walleye dermal sarcoma virus

Abstract

Walleye dermal sarcoma virus (WDSV) is a fish retrovirus associated with the development of tumors in walleyes. We have determined the complete nucleotide sequence of a DNA clone of WDSV, the N-terminal amino acid sequences of the major proteins, and the start site for transcription. The long terminal repeat is 590 bp in length, with the U3 region containing consensus sequences likely to be involved in viral gene expression. A predicted histidyl-tRNA binding site is located 3 nucleotides distal to the 3 end of the long terminal repeat. Virus particles purified by isopycnic sedimentation followed by rate zonal sedimentation showed major polypeptides with molecular sizes of 90, 25, 20, 14, and 10 kDa. N-terminal sequencing of these allowed unambiguous assignment of the small polypeptides as products of the gag gene, including CA and NC, and the large polypeptide as the TM product of env. The 582-amino-acid (aa) Gag protein precursor is predicted to be myristylated as is found for most retroviruses. NC contains a single Cys-His motif like those found in all retroviruses except spumaviruses. The WDSV pro and pol genes are in the same translational reading frame as gag and thus apparently are translated after termination suppression. The env gene encodes a surface (SU) protein of 469 aa predicted to be highly glycosylated and a large transmembrane (TM) protein of 754 aa. The sequence of TM is unusual in that it ends in a very hydrophobic segment of 65 residues containing a single charged residue . Following the env gene are two nonoverlapping long open reading frames of 290 aa (orf-A) and 306 aa (orf-B), neither of which shows significant sequence similarity with known genes. A third open reading frame of 119 aa (orf-C) is located in the leader region preceding gag. The predicted amino acid sequence of reverse transcriptase would place WDSV phylogenetically closest to the murine leukemia virus-related genus of retroviruses. However, other members of this genus do not have accessory genes, suggesting that WDSV acquired orf-A, orf-B, and perhaps orf-C late in its evolution. We hypothesize by analogy with other complex retroviruses that the accessory genes of WDSV function in the regulation of transcription and in RNA processing and also in the induction of walleye dermal sarcoma.

Seasonal Occurrence of Virally Induced Skin Tumors in Wild Fish

“…Retrovirus particles have been observed by Walker (1961) and later by Yamamoto et al (1985b) in walleye tumors. Walleye dermal sarcoma virus (WDSV) genome has been cloned directly from tumors and sequenced, showing that it is a complex retrovirus (Martineau et al 1991(Martineau et al , 1992Holzschu et al 1995). Virions of WDSV have been observed by electron microscopy, and the genome has been detected by in situ hybridization in tumors at high levels when collected in the spring (Poulet et al 1995).…”

“…Above 20ЊC, the viral enzyme activity dropped. It is also possible that the replication cycle of the virus may be restricted at higher temperatures, leading to the seasonal changes that are observed (Holzschu et al 1995).…”

Investigation of epizootic papillomatosis in bluegill Lepomis macrochirus (Rafinesque 1810) using next‐generation sequencing

“…Examples of herpesviral-induced neoplastic conditions include salmonid herpesvirus II and cyprinid herpesvirus I, both of which cause mortalities in young fish and papillomas in some older survivors (Kimura & Yoshimizu 1989;Sano et al 1991). The genus Epsilonretrovirus contains the complex retroviruses that infect fish (Edien et al 2010;Goff 2013), several of which have been partially or completely sequenced (Bowser & Casey 1993;Holzschu et al 1995;Basta et al 2009;Coffee et al 2013). The pathology of retroviralassociated tumours in fish has been reviewed by Coffee et al 2013.…”

Experimental Transmission of Walleye Dermal Sarcoma to Yellow Perch

“…Experimental transmission demonstrated that development of tumors on walleyes is greatest at water temperatures of 15ЊC, intermediate at 20ЊC, and least at 10ЊC (Bowser et al 1990). The causative virus is a member of the family Retroviridae, and the 12.7-kb genome has been completely sequenced (Holzschu et al 1995). Walleye discrete epidermal hyperplasia is a lesion found on walleyes that appears grossly as white areas on the body of the fish.…”