| Several members of the alphaherpesvirus sub-family infect and establish latency within the peripheral nervous system of their natural host. Periodic reactivation from latency can manifest in various forms ranging from mild (herpes labialis) to severe (shingles and encephalitis) disease. Neurotropic herpesviruses depend on longdistance axon transport for the initial establishment of latency in peripheral ganglia (retrograde transport) and for viral spread to exposed body surfaces following reactivation (anterograde transport). The mechanism of alphaherpesvirus transport in neuronal axons is poorly understood and is the focus of this dissertation.Time-lapse fluorescence microscopy was used to image actively translocating viral and cellular components in living neurons, allowing for several aspects of herpesvirus axon transport to be addressed. Here, we demonstrate that herpesviruses use two distinct pathways to move in axons. Following entry, exposure of the capsid to the cytosol results in efficient retrograde transport to neuronal cell bodies. In contrast, progeny viral particles move anterograde in axons following acquisition of virion envelope components and membrane lipids. These findings explain how viral particles are effectively trafficked to either sensory ganglia upon initial infection or peripheral sites of innervation following reactivation, as proper directional targeting in axons is coupled to viral disassembly and assembly processes. The finding that progeny virions use the host secretory pathway to travel to distal axons provides clarity to a long-standing controversy in the field regarding the point at which virions become fully assembled and infectious in neurons. While anterograde viral transport may occur by a constituitive cellular process, retrograde capsid transport is expected to be mediated by a viral component of the capsid transport complex. By identifying the post-entry transport complex and testing the role of several viral proteins in retrograde capsid trafficking, we provide the most likely candidate effectors for dynein-mediated capsid transport.The conservation of axon transport mechanisms was additionally addressed by performing analogous studies on pseudorabies virus (PRV) and herpes simplex virus type-1 (HSV-1). Although subtle differences exist, axon transport processes were largely conserved between these representatives of the two neuroinvasive herpesvirus genera: Simplexvirus (HSV-1) and Varicellovirus (PRV). |
