A dual-fluorescent recombinant for live observation of Herpes simplex-type 1 infection outcomes.

Abstract

Critical stages of lytic Herpes simplex type 1 (HSV-1) replication are marked by the sequential expression of immediate early (IE) to early (E), then late (L) viral genes. HSV-1 also persists in neuronal tissues via a non-replicative, transcriptionally repressed infection called latency. Understanding the regulation of lytic and latent transcriptional profiles provides focused insight into HSV-1 infection and disease. We sought a fluorescence-based approach to observe temporal progression of HSV-1 infection at the single-cell level. We constructed and characterized a novel HSV-1 recombinant that reports IE and L gene expression by fluorescent protein detection. The dual-reporter HSV-1 visualizes IE gene expression by a CMV promotor-driven YFP, and L gene expression by an endogenous mCherry-VP26 fusion. We confirmed that viral gene expression, replication and spread of infection in epithelial cells is not altered by the incorporation of the fluorescent reporters. Interference with viral DNA polymerase activity abolishes VP26-mCherry detection late in HSV-1 infection, visually reporting the failure to complete viral replication. Viral replication in primary neurons is not altered, but retrograde-directed inoculation of the dual-reporter HSV-1 exhibits a modest reduction in titer, compared to unlabeled HSV-1. Low-dose axonal inoculation in the presence of small molecule modulation of neuronal signaling results in divergent outcomes of YFP and mCherry detection, suggesting different states of latent and lytic replication. Rigorous characterization of this dual-reporter HSV-1 recombinant has demonstrated the utility of temporal observation of HSV-1 replication in live cells and the potential for further insight into the dynamics of infection. ImportanceHerpes simplex virus-type 1 (HSV-1) is a prevalent human pathogen that infects approximately 67% of the global population. HSV-1 invades the peripheral nervous system, where latent HSV-1 infection persists within the host for life. Immunological evasion, viral persistence, and herpetic pathologies are determined by regulation of HSV-1 gene expression. Studying HSV-1 gene expression during neuronal infection is challenging but essential for the development of antiviral therapeutics and interventions. We constructed and characterized a dual-fluorescent HSV-1 recombinant that enables visualization of IE and L gene expression. The recombinant HSV-1 is used to observe the progression and outcome of infection. We demonstrate that drug treatments targeting cellular pathways can manipulate latent HSV-1 infection in neurons to achieve divergent outcomes of infection.