Analysis of the role of the tegument compartment in intracellular alpha-herpesvirus capsid transport

Alpha-herpesviruses, such as herpes simplex virus-1 (HSV-1) and varicella zoster virus (VZV), are parasites of the mammalian peripheral nervous system (185). The alpha-herpesvirus virion has four elements. The DNA genome is housed within a protein shell known as the capsid, which is enclosed within a lipid bilayer envelope. In between the capsid and the envelope reside ∼20 viral proteins referred to as the tegument (86, 183, 249). Capsids must transport within the cytoplasm of an infected cell to replicate properly. During viral entry into a host cell, the envelope fuses with the cellular plasma membrane and deposits the capsid and tegument proteins into the cytoplasm (127). The capsid transports towards the nucleus where the viral genome is transferred from the inside of the capsid into the nucleus (127, 128, 132). After replication, genome-filled capsids are transported to the cell surface where they spread to a new cell (60, 78). Capsid transport is especially in sensory neurons, where capsids must transport distances up to 1 meter (61).; Although important to the pathogenesis of an alpha-herpesvirus, little is understood concerning the molecular mechanisms behind intracellular capsid transport. It is known that capsids use the endogenous cellular transport machinery including microtubules and microtubule motors; however, the viral proteins required for this process are unknown (8, 50, 199). The goal of my dissertation was to determine which viral proteins are effectors of capsid transport. I hypothesized that the tegument compartment of the alpha-herpesvirus virion was required for intracellular capsid transport. To address this hypothesis, I formulated three specific aims. (1) Determine if tegument proteins remain associated with capsids undergoing axonal transport. (2) Determine if capsids lacking tegument proteins undergo intracellular capsid transport. (3) Identify domains of VP1/2 required for intracellular capsid transport. I found that tegument proteins transport with capsids and that capsids lacking tegument proteins do not transport directionally. Finally, I identified multiple domains of VP1/2 that were required for capsid transport. These results are a starting point for the elucidation of the mechanism(s) of intracellular alpha-herpesvirus capsid transport. Ultimately, this work will provide a better understanding of alpha-herpesvirus pathogenesis as well as intracellular transport.