Varicella-Zoster Virus Gene Expression in Latently Infected Rat Dorsal Root Ganglia

Abstract

Latent infection of human ganglia with Varicella-Zoster virus (VZV) is characterized by a highly restricted pattern of viral gene expression. To enhance understanding of this process we used in situ hybridization (ISH) in a rat model of VZV latency to examine expression of RNA corresponding to eight different VZV genes in rat dorsal root ganglia (DRG) at various times after footpad inoculation with wild-type VZV. PCR in situ amplification was also used to determine the cell specificity of latent VZV DNA. It was found that the pattern of viral gene expression at 1 week after infection was different from that observed at the later times of 1 and 18 months after infection. Whereas multiple genes were expressed at 1 week after infection, gene expression was restricted at the later time points when latency had been established. At the later time points after infection the RNA transcripts expressed most frequently were those for VZV genes 21, 62, and 63. Gene 63 was expressed more than any other gene studied. While VZV DNA was detected almost exclusively in 5-10% of neurons, VZV RNA was detected in both neurons and nonneuronal cells at an approximate ratio of 3:1. A newly described monoclonal antibody to VZV gene 63-encoded protein was used to detect this protein in neuronal nuclei and cytoplasm in almost half of the DRG studied. These results demonstrate that (1) this rat model of latency has close similarities in terms of viral gene expression to human VZV latency which makes it a useful tool for studying this process and its experimental modulation and (2) expression of VZV gene 63 appears to be the single most consistent feature of VZV latency.

Varicella-Zoster Virus Open Reading Frame 2 Encodes a Membrane Phosphoprotein That Is Dispensable for Viral Replication and for Establishment of Latency

“…In contrast, ORF40 transcripts were present in ganglia from none of 18 VZV ROka-infected and 1 of 18 ROka2DA-infected cotton rats (data not shown). ORF63 RNA has been detected in ganglia from rats inoculated with VZV and humans (8,18,27), while ORF40 transcripts have rarely been associated with latent infection (7,18,19). Thus, the pattern of latent infection in cotton rats is similar to that reported previously.…”

Varicella-zoster virus infection of human neural cells in vivo

“…The observation that IE proteins were expressed in neural cells in the NOD-SCID mouse-human neural cell model while gE synthesis was reduced serves to validate reports about VZV gene transcription and translation in neural cells within human sensory ganglia obtained at autopsy and in animal models (2,4,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). Conclusions from autopsy specimens have been questioned because VZV gene expression might be triggered during the time required to obtain tissues, and infection of nonhuman neural cells in animals may not reproduce the VZV pathogenesis in the human host accurately.…”

“…Herpes simplex virus 1 produces latency-associated antisense mRNA transcripts (LATs) in neuronal cell nuclei, and viral proteins are not detected in human autopsy specimens or animal models of persistent infection (6). In contrast, VZV has no LAT sequence, and transcription or translation of VZV genes encoding the IE major transactivating protein, IE62, the IE63 coregulatory protein, and ORFs 4, 21, 29, 40, and 66 has been reported in ganglia (2,4,(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18).…”

The Immediate-Early 63 Protein of Varicella-Zoster Virus: Analysis of Functional Domains Required for Replication In Vitro and for T-Cell and Skin Tropism in the SCIDhu Model In Vivo

“…Similar interactions have been demonstrated for the related herpes simplex virus type 1 proteins ICP22 and ICP4 (24,36) and the equine herpesvirus 1 proteins IECP22 and IEP (10,19,25,37,39,45). Understanding IE63 functions is of particular interest because of the evidence that it is expressed during latency in human ganglia and in the rat model (16,26,28,43).…”