title: Rhabdovirus-like endogenous viral elements in the genome of Spodoptera frugiperda insect cells are actively transcribed: Implications for adventitious virus detection.
abstract: Spodoptera frugiperda (Sf) cell lines are used to produce several biologicals for human and veterinary use. Recently, it was discovered that all tested Sf cell lines are persistently infected with Sf-rhabdovirus, a novel rhabdovirus. As part of an effort to search for other adventitious viruses, we searched the Sf cell genome and transcriptome for sequences related to Sf-rhabdovirus. To our surprise, we found intact Sf-rhabdovirus N- and P-like ORFs, and partial Sf-rhabdovirus G- and L-like ORFs. The transcribed and genomic sequences matched, indicating the transcripts were derived from the genomic sequences. These appear to be endogenous viral elements (EVEs), which result from the integration of partial viral genetic material into the host cell genome. It is theoretically impossible for the Sf-rhabdovirus-like EVEs to produce infectious virus particles as 1) they are disseminated across 4 genomic loci, 2) the G and L ORFs are incomplete, and 3) the M ORF is missing. Our finding of transcribed virus-like sequences in Sf cells underscores that MPS-based searches for adventitious viruses in cell substrates used to manufacture biologics should take into account both genomic and transcribed sequences to facilitate the identification of transcribed EVE's, and to avoid false positive detection of replication-competent adventitious viruses.
authors.affiliation: GlycoBac LLC, 1938 Harney Street, Laramie, WY 82072, USA. Electronic address: christophgeisler@gmail.com.
authors.forename: Christoph
authors.initials: C
authors.lastname: Geisler
authors.affiliation: GlycoBac LLC, 1938 Harney Street, Laramie, WY 82072, USA; University of Wyoming, Department of Molecular Biology, 1000 E. University Avenue, Laramie, WY 82071, USA.
authors.forename: Donald L
authors.initials: DL
authors.lastname: Jarvis
mesh_terms: D000818:Animals; D002460:Cell Line; D020077:Endogenous Retroviruses / Q000235:genetics; D015967:Gene Expression Regulation, Viral; D005814:Genes, Viral / Q000235:genetics*; D049750:Genome, Insect / Q000235:genetics*; D016366:Open Reading Frames / Q000235:genetics; D010802:Phylogeny; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012209:Rhabdoviridae / Q000235:genetics; D018411:Spodoptera / Q000166:cytology / Q000235:genetics*; D014158:Transcription, Genetic; D059467:Transcriptome / Q000235:genetics*; D014764:Viral Proteins / Q000145:classification / Q000235:genetics; D014771:Virion / Q000235:genetics; D014780:Viruses / Q000235:genetics
chemical_list: D014764:Viral Proteins
keywords: Adventitious virus; Baculovirus insect cell system; Endogenous viral element; Massively parallel sequencing; Sf-rhabdovirus; Spodoptera frugiperda cells