Submitted to: Journal of Insect Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/16/2002
Publication Date: 5/1/2003
Citation: Gundersen, D.E., Lynn, D.E. 2003. Polydnavirus integration in lepidopteran host cells in vitro. Journal of Insect Physiology. Interpretive Summary: Parasitic wasps have great potential for the control of moth species that are pests of agricultural crops and forests. The survival of many of these parasites is enhanced by a virus, called a polydnavirus, that is injected along with the wasp egg into the host caterpillar. In the current paper, cell culture studies have revealed that the genetic material of the virus becomes integrated into the host cell during the infection process. Additionally, we showed that the integrated genes persist even after years in culture. A mechanism for this integration process is proposed. This new knowledge may help to explain how the virus assists in the wasp's survival, information which may lead to new biocontrol strategies based on wasp disruption of insect pest immune systems. Understanding how the virus inserts its genetic material into caterpillar cells could allow scientists to use the virus as a vector to continuously make a desired protein, such as a pharmaceutical, in the laboratory. This information will be of interest to scientists and biotechnology companies who will be able to use this system as an alternative to current methods for producing scarce or valuable proteins.
Technical Abstract: The long-term persistence of polydnavirus (PDV)DNA in infected lepidopteran cell cultures has suggested that at least some of the virus sequences become integrated permanently into the cell genome. In the current study, we provide supportive evidence of this event. Clone libraries were isolated from two different gypsy moth cell lines that had been maintained in continuous culture for more than five years after infection with Glyptapanteles indiensis PDV (GiPDV. Junction clones containing both cellular and viral sequences were isolated. Precise integration junction sites were identified by sequence comparison of linear (integrated) and circular forms of the GiPDV genome segment F, from which viral sequences originated. Host sequences at the site of integration varied between the two cell lines but virus sequence junctions were identical and contained a 4-base pair CATG palindromic repeat. The GiPDV segment F does not encode any self-insertion proteins, suggesting a host-derived mechanism is responsible for its in vitro integration. The cellular site of one junction clone contained sequences indicative of a retrotransposon, including a putative reverse transcriptase/integrase upstream of the site of viral integration. A potential mechanism is suggested for the integration of PDV DNA in vitro. It remains to be seen if integration of the virus also occurs in the lepidopteran host in vivo.