Identification and Characterization of an Exogenous Retrovirus from Atlantic Salmon Swim Bladder Sarcomas

Abstract

A novel piscine retrovirus has been identified in association with an outbreak of leiomyosarcoma in the swim bladders of Atlantic salmon. The complete nucleotide sequence of the Atlantic salmon swim bladder sarcoma virus (SSSV) provirus is 10.9 kb in length and shares a structure and transcriptional profile similar to those of murine leukemia virus-like simple retroviruses. SSSV appears unique to simple retroviruses by not harboring sequences in the Atlantic salmon genome. Additionally, SSSV differs from other retroviruses in potentially utilizing a methionine tRNA primer binding site. SSSV-associated tumors contain high proviral copy numbers (greater than 30 per cell) and a polyclonal integration pattern. Phylogenetic analysis based on reverse transcriptase places SSSV with zebrafish endogenous retrovirus (ZFERV) between the Gammaretrovirus and Epsilonretrovirus genera. Large regions of continuous homology between SSSV and ZFERV Gag, Pol, and Env suggest that these viruses represent a new group of related piscine retroviruses.

Retroviruses of wild and cultured fish

“…The second outbreak of swim bladder sarcoma was noticed in 1996 in juvenile salmon collected from the Pleasant River in Maine and maintained at the North Attleboro National Fish Hatchery in Massachusetts (Paul et al 2006). Diseased animals exhibited physical symptoms similar to those of the previous report on salmon swim-bladder sarcoma.…”

“…Diseased animals exhibited physical symptoms similar to those of the previous report on salmon swim-bladder sarcoma. Histologically, the multinodular masses localizing on or replacing the swim bladder were composed of well-differentiated fibroblastic cells arranged in interlacing bundles (Paul et al 2006). By the spring of 1998, cumulative mortality reached 35% of the population.…”

“…By the spring of 1998, cumulative mortality reached 35% of the population. Samples provided from the affected fish were used to obtain a complete nucleotide sequence of the virus (Paul et al 2006). They found that SSSV is a simple retrovirus, 10.9 kb in length, containing three open reading frames (gag, pro-pol, env) flanked by LTR sequences at each end of the genome.…”

“…Thus, it is possible that other factors (e.g. host, environmental conditions) may play a role in the etiology of salmon swim bladder sarcoma (Paul et al 2006). …”

Horizontal gene transfers and cell fusions in microbiology, immunology and oncology (Review)

“…In the zebrafish exists a related apathogenic endogenous retrovirus (ZFERV). Further sarcomagenic piscine epsilon retroviruses are the walleye dermal sarcoma virus (WDSV) and the walleye epidermal hyperplasia viruses (WEHV) type I and II (113,(130)(131)(132)(133). The SSSV Env protein shows 39% amino acid sequence homology to ZFERV, and more distant (21% homology) to MPMV (Mason-Pfizer monkey virus) (see below).…”