To map complex neural circuitry, scientists sometimes rely on a technique called viral tracing, following a virus as it replicates and infects connecting cells. While this method has been used successfully in vertebrates, researchers have had limited success in metazoans such as Drosophila. The problem is that it is difficult to inject viruses into such a small host with any specificity, and techniques using transgenic replicons don’t create the infectious particles necessary for tracing. To tackle these issues, Thomas Clandinin, assistant professor of neurobiology at the Stanford School of Medicine, and his team wondered if the cells might assemble infectious particles of the Sindbis arbovirus all by themselves.
“Logically, there’s no reason why you can’t put the whole virus genome under the control of the cell and then assemble the virus particle,” said Clandinin. “We saw that it had been done in yeast and plants, but it’s very different trying to do it in a multi-cell organism where you want to do it tissue specifically.”
The group piggybacked on existing transgenic replicon technologies to add viral structural proteins into the Drosophila genome. By doing so, they were able to induce self-assembly of infectious virus particles inside the cells.
Clandinin was surprised by their success. “There’s a lot of regulation that goes into the production and timing of virus proteins, and if the virus genome is under host control, you are eliminating some of that regulation,” he said. “So we were very happy to discover that we could make these infectious particles without ever having started with any infectious particles to begin with. And our success, I think, speaks to the possibility of doing this with other systems and other viruses.”
The researchers next plan to develop a Drosophila transsynaptic tracer using the technique. The team is also looking into reengineering aspects of arboviruses that influence replication and spreading between neurons as well as using mutated particles to better study how Drosophila neurons connect and communicate.
Wernet MF, Klovstad M, Clandinin TR. Generation of infectious virus particles from inducible transgenic genomes. Curr Biol. 2014 Feb 3;24(3):R107-8.