Pseudorabies Virus Membrane Proteins gI and gE Facilitate Anterograde Spread of Infection in Projection- Specific Neurons in the Rat

Abstract

The membrane proteins gI and gE of Pseudorabies virus (PRV) are required for viral invasion and spread through some neural pathways of the rodent central nervous system. Following infection of the rat retina with wild-type PRV, virus replicates in retinal ganglion neurons and anterogradely spreads to infect all visual centers in the brain. By contrast, gI and gE null mutants do not infect a specific subset of the visual centers, e.g., the superior colliculus and the dorsal lateral geniculate nucleus. In previous experiments, we suggested that the defect was not due to inability to infect projection-specific retinal ganglion cells, because mixed infection of a gE deletion mutant and a gI deletion mutant restored the wild-type phenotype (i.e., genetic complementation occurred). In the present study, we provide direct evidence that gE and gI function to promote the spread of infection after entry into primary neurons. We used stereotaxic central nervous system injection of a fluorescent retrograde tracer into the superior colliculus and subsequent inoculation of a PRV gI-gE double null mutant into the eye of the same animal to demonstrate that viral antigen and fluorescent tracer colocalize in retinal ganglion cells. Furthermore, we demonstrate that direct injection of a PRV gI-gE double null mutant into the superior colliculus resulted in robust infection followed by retrograde transport to the eye and replication in retinal ganglion neuron cell bodies. These experiments provide additional proof that the retinal ganglion cells projecting to the superior colliculus are susceptible and permissive to gE and gI mutant viruses. Our studies confirm that gI and gE specifically facilitate anterograde spread of infection by affecting intracellular processes in the primary infected neuron such as anterograde transport in axons or egress from axon terminals.Alphaherpesviruses, like Herpes simplex virus types 1 and 2 (HSV-1 and HSV-2), Varicella-zoster virus, and Pseudorabies virus (PRV), exhibit a predilection to infect neurons in the central nervous system (CNS) and peripheral nervous system (PNS) of an animal host (9a). During natural infections, virus replicates in nonneuronal cells and then undergoes retrograde spread of virus into afferent (e.g., sensory) or efferent (e.g., motor) nerve fibers innervating the infected tissue. Typically, this viral infection is limited to the PNS, where a latent infection is established in neurons directly innervating the peripheral site. Reactivation from latency is associated with virus replication in the primary neuron followed by anterograde transport of newly synthesized virus particles from the neuronal cell body back to the innervated tissue. Although less frequent, virus may also spread from the PNS to the CNS following primary infection or reactivation; this often has fatal consequences for the host. Hence, alphaherpesviruses are likely to encode mechanisms that facilitate travel in either direction within a neural circuit and thus may regulate the choice of direction at differe...

Directed Egress of Animal Viruses Promotes Cell-to-Cell Spread

“…PRV gE/gI and a second membrane protein, US9, which also contains tyrosine, dileucine, and acidic motifs (reviewed in reference 10), are involved in sorting decisions made in neurons (reviewed in reference 89). Elegant studies in the rodent nervous system have shown that gE/gI and US9 are involved in determining movement of nascent virions within the complex neuronal circuitry (10,14,25,44,(85)(86)(87)(88). There are many similarities between sorting decisions made in neurons and those made in epithelial cells, but there are also significant differences (14,21,68,(85)(86)(87)(88).…”

Virion-Incorporated Glycoprotein B Mediates Transneuronal Spread of Pseudorabies Virus

“…Therefore, in the absence of any of these proteins, infection cannot be transmitted efficiently from a presynaptic to a postsynaptic cell (3,23). Another viral membrane protein required for the transneuronal spread of PRV is gB (2, 21).…”

Two Modes of Pseudorabies Virus Neuroinvasion and Lethality in Mice

“…Spread of infection of wild-type virus in the anterograde direction (from presynaptic to postsynaptic neurons) requires the PRV U S 9, gE, and gI proteins (4,12). These genes are deleted in the PRV-Bartha strain (3,14,16,18,19,22).…”