Doucet Daniel, Levasseur Anic, Béliveau Catherine, Lapointe Renée, Stoltz Don, Cusson Michel
Department of Microbiology and Immunology, Sir Charles Tupper Medical Building, Dalhousie University, Halifax, NS B3H 4H7, Canada.
Natural Resources Canada, Canadian Forest Service, Laurentian Forestry Centre, 1055 du PEPS, PO Box 10380, Stn Ste-Foy, Quebec City, QC G1V 4C7, Canada.
J Gen Virol. 2007 Jan;88(Pt 1):105-113. doi: 10.1099/vir.0.82314-0.
Polydnaviruses (PDVs) are dsDNA viruses transmitted by ichneumonid and braconid endoparasitoids to their lepidopteran hosts during oviposition. Wasp carriers are asymptomatic and transmit the virus to their progeny through the germ line; replication is confined to the calyx region of the wasp ovary, where the virus accumulates in the fluid bathing the eggs. In the lepidopteran host, however, no virus replication takes place, but PDV gene expression is essential for successful parasitism. Sustained gene expression in the absence of virus replication thus requires that the circular PDV genome segments persist for days within host cells. Available evidence suggests that most genome segments persist as episomes, but recent studies have indicated that some genome segments may undergo integration within lepidopteran genomic DNA, at least in vitro. In the present study, an integrated form of a Tranosema rostrale ichnovirus (TrIV) genome segment was cloned from genomic DNA extracted from infected Choristoneura fumiferana CF-124T cells and junction regions on either side of the viral DNA sequence were sequenced. This is the first proven example of integration of an ichnovirus genome segment in infected lepidopteran cells. Interestingly, circular forms of this genome segment do not appear to persist in these cells; none the less, a gene (TrFrep1) carried by this genome segment displays long-term transcription in infected cultured cells.
多DNA病毒（PDVs）是双链DNA病毒，由姬蜂科和茧蜂科内寄生蜂在产卵时传播给它们的鳞翅目宿主。黄蜂携带者没有症状，并通过种系将病毒传播给它们的后代；病毒复制局限于黄蜂卵巢的萼区，病毒在浸泡卵的液体中积累。然而，在鳞翅目宿主中，病毒不进行复制，但PDV基因表达对于成功寄生至关重要。因此，在没有病毒复制的情况下持续的基因表达要求环状PDV基因组片段在宿主细胞内持续存在数天。现有证据表明，大多数基因组片段以附加体的形式存在，但最近的研究表明，至少在体外，一些基因组片段可能会整合到鳞翅目基因组DNA中。在本研究中，从感染的云杉色卷蛾CF-124T细胞中提取的基因组DNA中克隆了一种玫瑰色线虫姬蜂病毒（TrIV）基因组片段的整合形式，并对病毒DNA序列两侧的连接区域进行了测序。这是首次在感染的鳞翅目细胞中证实姬蜂病毒基因组片段整合的例子。有趣的是，该基因组片段的环状形式似乎不会在这些细胞中持续存在；尽管如此，该基因组片段携带的一个基因（TrFrep1）在感染的培养细胞中显示出长期转录。
