Molecular Biology of Jaagsiekte Sheep Retrovirus

Jaagsiekte sheep retrovirus (JSRV) is the causative agent of ovine pulmonary adenocarcinoma (OPA), a contagious lung cancer of sheep. Until recently, research on JSRV/OPA was hampered by the lack of a tissue culture system for the propagation of the virus. Historically, pathological samples (lung fluid) collected from sheep affected by OPA were the only source of infectious JSRV. Thus studies on the JSRV/OPA system were conducted only where field isolates of OPA cases were readily available. In the past 10 years, the deduction of the JSRV sequence (York et al. 1991; York 1992), the isolation of an infectious and oncogenic JSRV molecular clone (JSRV21) (Palmarini et al. 1999a) and the establishment of a rapid method to produce infectious virus in vitro (Palmarini et al. 1999a) sparked many studies at the molecular level that strengthened past observations and revealed new properties of this unique virus. Here, we will review the data accumulated so far on the molecular biology of JSRV using the infectious and oncogenic JSRV21 molecular clone as virus of reference.