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Jennifer H. LaVail, Guiqing Huang, Jolene M. Draper; A Quantitative Assessment of the Role of Us9 in Anterograde Spread of HSV DNA in Neurons. Invest. Ophthalmol. Vis. Sci. 2011;52(14):2968.
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In the case of recurrent herpetic keratitis, Herpes simplex virus (HSV) must first travel retrograde from a peripheral site of infection in corneal epithelial cells to innervating sensory nerve cell bodies, and after replication, travel anterograde within the same sensory axons back to the periphery. How the virus is assembled for long distance axonal transport is controversial. One possibility is that the complete virion is encased in a host cell vesicle for transport. Alternatively, the virus may travel as subassemblies, the nucleocapsid independent of a vesicular organelle containing viral envelope proteins. We have identified a specific viral protein, Us9, which facilitates the anterograde transport of HSV. If the subassembly model is correct, viral mutants that lack the Us9 gene should displayed impaired transport of viral DNA. Conflicting results have been reported. McGraw et al. mutated Us9 in the NS strain of HSV and found Us9 was not required for transport of infective virus (1). We found that mutation of the Us9 gene in the F strain resulted in severely impaired anterograde transport of infective virus. Our goal was to compare quantitatively the anterograde transport of DNA delivered to axons after infection with these two strains of HSV in an in vivo model.
Murine retinas were pulse infected with F-Us9-null, NS-Us9-null or F-Us9-R (wt ) at equivalent doses of virus/eye. Three days post infection (dpi), the optic tracts (OT) were dissected, lysed and prepared for PCR analysis. Ten OTs were pooled and each experiment was repeated 3 times.
Three dpi with F-Us9-R, each OT contained about 225 ng of DNA, including about 14 ng of Us9R DNA. Three dpi with NS-Us9-null virus, each OT contained about 225 ng and contained about 35 pg of viral DNA. After 3 dpi with F-Us9-null HSV we were unable to detect viral DNA in the OTs.
Thus, the NS-Us9-null strain retains the ability to transport viral DNA. However with the F-Us9-null strain, no viral DNA was detected in the optic tracts of mice. This difference may be related to different viral background strains. Together with our data showing viral glycoproteins in the OTs at 3 dpi with F-Us9-R and F-Us9-null strains of HSV virus, these findings support the subassembly model for delivery of new virus to axons.1 McGraw, H. M. et al. J. Virol. 83:8315, 2009.
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