After primary replication at the site of entry into the host, alphaherpesviruses infect and establish latency in neurons. To this end, they are transported within axons retrograde from the periphery to the cell body for replication and in an anterograde direction to synapses for infection of higher-order neurons or back to the periphery. Retrograde transport of incoming nucleocapsids is well documented. In contrast, there is still significant controversy on the mode of anterograde transport. By high-resolution transmission electron microscopy of primary neuronal cultures from embryonic rat superior cervical ganglia infected by pseudorabies virus (PrV), we observed the presence of enveloped virions in axons within vesicles supporting the "married model" of anterograde transport of complete virus particles within vesicles (C. Maresch, H. Granzow, A. Negatsch, B.G. Klupp, W. Fuchs, J.P. Teifke, and T.C. Mettenleiter, J. Virol. 84:5528-5539, 2010). We have now extended these analyses to the related human herpes simplex virus type 1 (HSV-1). We have demonstrated that in neurons infected by HSV-1 strains HFEM, 17؉ or SC16, approximately 75% of virus particles observed intraaxonally or in growth cones late after infection constitute enveloped virions within vesicles, whereas approximately 25% present as naked capsids. In general, the number of HSV-1 particles in the axons was significantly less than that observed after PrV infection.Herpesviruses are characterized by a distinct virion morphology and the property to establish latent infections with episodes of spontaneous reactivation. Herpesvirus virions contain a DNA genome enclosed in an icosahedral capsid shell, which is in turn embedded in tegument proteins and surrounded by a lipid envelope containing virally encoded, mostly glycosylated proteins. Within the Herpesviridae, three subfamilies, designated the Alpha-, Beta-, and Gammaherpesvirinae, have been recognized (9). The alphaherpesviruses contain pathogens of humans and animals with neuroinvasive properties resulting in infection of and latency in neurons. The genus Simplexvirus encompasses the ubiquitous human herpes simplex viruses, types 1 and 2 (HSV-1 and HSV-2), whereas varicella-zoster virus and several relevant animal pathogens, e.g., the porcine pseudorabies virus (PrV) (Suid herpesvirus 1 [30]), belong to the genus Varicellovirus.Alphaherpesviruses are pantropic but neuroinvasive, i.e., they infect the nervous system after primary replication in mucosal membranes. Neuroinvasion entails two long-distance transport processes of different directionalities (3). There is general consent that retrograde intraaxonal transport of incoming alphaherpesvirus particles to the neuronal cell body for productive replication or establishment of latent infection is effected by dynein-mediated microtubule-associated transport of nucleocapsids coated with "inner" tegument proteins (1,14,26), as occurs during infection of nonpolarized cultured cells (reviewed in reference 39). After reactivation from latency, anterograde...

A hallmark of alphaherpesviruses is their capacity to be neuroinvasive and establish latent infections in neurons. After primary replication in epithelial cells at the periphery, entry into nerve endings occurs, followed by retrograde transport of nucleocapsids to the nucleus where viral transcription, genome replication, and nucleocapsid formation take place. Translocation of nucleocapsids to the cytoplasm is followed by axonal transport to infect synaptically linked neurons. Two modes of intraaxonal anterograde herpesvirus transport have been proposed: transport of complete, enveloped virions within vesicles ("married model"), and separate transport of capsids and envelopes ("subassembly model"). To assess this in detail for the alphaherpesvirus pseudorabies virus (PrV), we used high-resolution transmission electron microscopy of primary neuronal cultures from embryonic rat superior cervical ganglia after infection with wild-type and gB-deficient PrV. Our data show that intranuclear capsid maturation, nuclear egress and cytoplasmic secondary envelopment occur as in cultured nonpolarized cells (H. Most members of the subfamily Alphaherpesvirinae within the family Herpesviridae in the order Herpesvirales (8) are characterized by a pronounced neurotropism. They include the type member of the genus Simplexvirus, the human herpes simplex virus type 1 (HSV-1), as well as varicella-zoster virus, as type member of the genus Varicellovirus. After initial replication in mucosal membranes, these viruses infect sensory nerve endings and enter the peripheral nervous system by retrograde axonal transport. In sensory ganglia they replicate productively or establish latency (reviewed in reference 13). During occasional reactivation newly replicated virions are transported via fast anterograde axonal transport to the original site of infection causing recurrent herpetic lesions (reviewed in reference 11). In some cases, HSV-1 is transported to the central nervous system, causing viral encephalitis (13,20). Suid herpesvirus 1, also designated as pseudorabies virus (PrV), is a member of the genus Varicellovirus within the Alphaherpesvirinae. In swine, its natural host, it causes Aujeszky's disease, which, depending on the age of the pig and the virulence of the virus, can manifest itself as a severe meningoencephalitis, rapidly leading to death of the animal. Besides pigs, PrV is able to productively infect a broad spectrum of mammalian species, not including equids and higher primates, resulting in invariably fatal infections (26).HSV-1 and PrV have become models to analyze basic features of herpesvirus replication, including entry, virion formation, and egress (28). Infection occurs primarily by pH-independent fusion of the viral envelope with the plasma membrane. In the alphaherpesviruses four glycoproteins, gB, gD, and the gH/gL-complex have been shown to be required for entry (27). gB is essential for penetration and cell-to-cell spread and is the most highly conserved glycoprotein found in herpesviruses (27). Virus mutants...

The membrane protein encoded by the US9 gene of alphaherpesviruses plays an important role during virion assembly and transport in neurons. Here, we demonstrate that in herpes simplex virus type 1 (HSV-1) strain KOS, due to base substitutions, the predicted TATA-box of US9 is mutated, and a premature stop is present at codon 58 of US9, which contains 91 codons in other HSV-1 strains. The TATA-box mutation also removes the native stop codon of the adjacent US8A gene, leading to extension of the coding region from 160 to 191 codons. Northern blot analyses revealed reduced transcription of US9 in cells infected with HSV-1 KOS. Moreover, a US9-specific antiserum did not detect any gene products in Western blot and immunofluorescence analyses of KOS-infected cells, indicating that the truncated protein is not stable. In contrast, Western blot reactions of a pUS8A-specific antiserum confirmed enlargement of this protein in HSV-1 KOS.