Faculty Bibliography

Adenovirus is a nuclear replicating DNA virus reliant on host RNA processing machinery. Processing and metabolism of cellular RNAs can be regulated by METTL3, which catalyzes the addition of N6-methyladenosine (m⁶A) to mRNAs. While m⁶A-modified adenoviral RNAs have been previously detected, the location and function of this mark within the infectious cycle is unknown. Since the complex adenovirus transcriptome includes overlapping spliced units that would impede accurate m⁶A mapping using short-read sequencing, here we profile m⁶A within the adenovirus transcriptome using a combination of meRIP-seq and direct RNA long-read sequencing to yield both nucleotide and transcript-resolved m⁶A detection. Although both early and late viral transcripts contain m⁶A, depletion of m⁶A writer METTL3 specifically impacts viral late transcripts by reducing their splicing efficiency. These data showcase a new technique for m⁶A discovery within individual transcripts at nucleotide resolution, and highlight the role of m⁶A in regulating splicing of a viral pathogen.

The genomes of DNA viruses encode deceptively complex transcriptomes evolved to maximize coding potential within the confines of a relatively small genome. Defining the full range of viral RNAs produced during an infection is key to understanding the viral replication cycle and its interactions with the host cell. Traditional short-read (Illumina) sequencing approaches are problematic in this setting due to the difficulty of assigning short reads to individual RNAs in regions of transcript overlap and to the biases introduced by the required recoding and amplification steps. Additionally, different methodologies may be required to analyze the 5' and 3' ends of RNAs, which increases both cost and effort. The advent of long-read nanopore sequencing simplifies this approach by providing a single assay that captures and sequences full length RNAs, either in cDNA or native RNA form. The latter is particularly appealing as it reduces known recoding biases whilst allowing more advanced analyses such as estimation of poly(A) tail length and the detection of RNA modifications including N⁶ -methyladenosine. Using herpes simplex virus (HSV)-infected primary fibroblasts as a template, we provide a step-by-step guide to the production of direct RNA sequencing libraries suitable for sequencing using Oxford Nanopore Technologies platforms and provide a simple computational approach to deriving a high-quality annotation of the HSV transcriptome from the resulting sequencing data. © 2020 by John Wiley & Sons, Inc. Basic Protocol 1: Productive infection of primary fibroblasts with herpes simplex virus Support Protocol: Cell passage and plating of primary fibroblasts Basic Protocol 2: Preparation and sequencing of dRNA-seq libraries from virus-infected cells Basic Protocol 3: Processing, alignment, and analysis of dRNA-seq datasets.

Meeting Report on the 9th Annual Symposium of the Colorado Alphaherpesvirus Latency Society (CALS) held on May 8-11, 2019, in Vail, CO.

We describe a primary neuronal culture system suitable for molecular characterization of herpes simplex virus type 1 (HSV-1) infection, latency, and reactivation. While several alternative models are available, including infections of live animal or explanted ganglia, these are complicated by the presence of multiple cell types, including immune cells, and difficulties in manipulating the neuronal environment. The highly pure neuron culture system described here can be readily manipulated and is ideal for molecular studies that focus exclusively on the relationship between the virus and host neuron, the fundamental unit of latency. As such this model allows for detailed investigations of both viral and neuronal factors involved in the establishment and maintenance of HSV-1 latency and in viral reactivation induced by defined stimuli.

The mTOR pathway integrates both extracellular and intracellular signals and serves as a central regulator of cell metabolism, growth, survival, and stress responses. Neurotropic viruses, such as herpes simplex virus-1 (HSV-1), also rely on cellular AKT-mTORC1 signaling to achieve viral latency. Here, we define a novel genotoxic response whereby spatially separated signals initiated by extracellular neurotrophic factors and nuclear DNA damage are integrated by the AKT-mTORC1 pathway. We demonstrate that endogenous DNA double-strand breaks (DSBs) mediated by Topoisomerase 2β-DNA cleavage complex (TOP2βcc) intermediates are required to achieve AKT-mTORC1 signaling and maintain HSV-1 latency in neurons. Suppression of host DNA-repair pathways that remove TOP2βcc trigger HSV-1 reactivation. Moreover, perturbation of AKT phosphorylation dynamics by downregulating the PHLPP1 phosphatase led to AKT mis-localization and disruption of DSB-induced HSV-1 reactivation. Thus, the cellular genome integrity and environmental inputs are consolidated and co-opted by a latent virus to balance lifelong infection with transmission.

Characterizing complex viral transcriptomes by conventional RNA sequencing approaches is complicated by high gene density, overlapping reading frames, and complex splicing patterns. Direct RNA sequencing (direct RNA-seq) using nanopore arrays offers an exciting alternative whereby individual polyadenylated RNAs are sequenced directly, without the recoding and amplification biases inherent to other sequencing methodologies. Here we use direct RNA-seq to profile the herpes simplex virus type 1 (HSV-1) transcriptome during productive infection of primary cells. We show how direct RNA-seq data can be used to define transcription initiation and RNA cleavage sites associated with all polyadenylated viral RNAs and demonstrate that low level read-through transcription produces a novel class of chimeric HSV-1 transcripts, including a functional mRNA encoding a fusion of the viral E3 ubiquitin ligase ICP0 and viral membrane glycoprotein L. Thus, direct RNA-seq offers a powerful method to characterize the changing transcriptional landscape of viruses with complex genomes.

Transcriptome profiling has become routine in studies of many biological processes. However, favored approaches such as short-read Illumina RNA sequencing are giving way to long-read sequencing platforms better suited to interrogating the complex transcriptomes typical of many RNA and DNA viruses. Here, we provide a guide - tailored to molecular virologists - to the ins-and-outs of viral transcriptome sequencing and discuss the strengths and weaknesses of the major RNA sequencing technologies as tools to analyze the abundance and diversity of viral transcripts made during infection.

Herpes simplex virus 1 (HSV-1) is a widespread pathogen that persists for life, replicating in surface tissues and establishing latency in peripheral ganglia. Increasingly, molecular studies of latency use cultured neuron models developed using recombinant viruses such as HSV-1 GFP-US11, a derivative of strain Patton expressing green fluorescent protein (GFP) fused to the viral US11 protein. Visible fluorescence follows viral DNA replication, providing a real time indicator of productive infection and reactivation. Patton was isolated in Houston, Texas, prior to 1973, and distributed to many laboratories. Although used extensively, the genomic structure and phylogenetic relationship to other strains is poorly known. We report that wild type Patton and the GFP-US11 recombinant contain the full complement of HSV-1 genes and differ within the unique regions at only eight nucleotides, changing only two amino acids. Although isolated in North America, Patton is most closely related to Asian viruses, including KOS63.

Infection with herpes simplex virus-1 (HSV-1) brings numerous changes in cellular gene expression. Levels of most host mRNAs are reduced, limiting synthesis of host proteins, especially those involved in antiviral defenses. The impact of HSV-1 on host microRNAs (miRNAs), an extensive network of short non-coding RNAs that regulate mRNA stability/translation, remains largely unexplored. Here we show that transcription of the miR-183 cluster (miR-183, miR-96, and miR-182) is selectively induced by HSV-1 during productive infection of primary fibroblasts and neurons. ICP0, a viral E3 ubiquitin ligase expressed as an immediate-early protein, is both necessary and sufficient for this induction. Nuclear exclusion of ICP0 or removal of the RING (really interesting new gene) finger domain that is required for E3 ligase activity prevents induction. ICP0 promotes the degradation of numerous host proteins and for the most part, the downstream consequences are unknown. Induction of the miR-183 cluster can be mimicked by depletion of host transcriptional repressors zinc finger E-box binding homeobox 1 (ZEB1)/-crystallin enhancer binding factor 1 (deltaEF1) and zinc finger E-box binding homeobox 2 (ZEB2)/Smad-interacting protein 1 (SIP1), which we establish as new substrates for ICP0-mediated degradation. Thus, HSV-1 selectively stimulates expression of the miR-183 cluster by ICP0-mediated degradation of ZEB transcriptional repressors.

Herpes simplex virus 1 (HSV-1) uses latency in peripheral ganglia to persist in its human host, however, recurrent reactivation from this reservoir can cause debilitating and potentially life-threatening disease. Most studies of latency use live-animal infection models, but these are complex, multilayered systems and can be difficult to manipulate. Infection of cultured primary neurons provides a powerful alternative, yielding important insights into host signaling pathways controlling latency. However, small animal models do not recapitulate all aspects of HSV-1 infection in humans and are limited in terms of the available molecular tools. To address this, we have developed a latency model based on human neurons differentiated in culture from an NIH-approved embryonic stem cell line. The resulting neurons are highly permissive for replication of wild-type HSV-1, but establish a non-productive infection state resembling latency when infected at low viral doses in the presence of the antivirals acyclovir and interferon-alpha. In this state, viral replication and expression of a late viral gene marker are not detected but there is an accumulation of the viral latency-associated transcript (LAT) RNA. After a six-day establishment period, antivirals can be removed and the infected cultures maintained for several weeks. Subsequent treatment with sodium butyrate induces reactivation and production of new infectious virus. Human neurons derived from stem cells provide the appropriate species context to study this exclusively human virus with the potential for more extensive manipulation of the progenitors and access to a wide range of preexisting molecular tools.