Biology subjects

Hawes, P. C.

Publications and source records attributed to Hawes, P. C..

6 recordsLinked to original sources

bioRxiv2026

Coronavirus spherules are supported by a novel triple-layer protein lattice

Coronaviruses (CoVs) cause significant disease in humans and animals, with a track-record of cross-species transmission. Despite their global significance, available control strategies are limited, especially for emerging CoVs. A deeper fundamental understanding of the virus life cycle is essential to underpin development of control measures. A critical step of the CoV life cycle is the rearrangement of host cell membranes into replication organelles (ROs). This is conserved across all CoVs and ROs comprise double membrane vesicles (DMVs), the site of viral RNA synthesis, and double membrane spherules. CoV spherules are complex structures requiring both positive and negative curvature of paired membranes so are predicted to have a high energy cost to maintain. To date they have an entirely unknown function. Interestingly, although always present, abundance of spherules in CoV infected cells varies with Betacoronavirus Middle East Respiratory Syndrome coronavirus, Gammacoronavirus infectious bronchitis virus (IBV) and porcine deltacoronavirus in particular producing a considerable number. Here, using cryo-bioimaging we identified for the first time that CoV spherules are embedded with a complex and organised triple-layered protein lattice and that spherules always contain a cargo that appears arranged as a shell inside the vesicle. In addition, we confirmed the presence of a double membrane spanning molecular pore in Gammacoronavirus DMVs and further identified a population of potential DMV formation intermediates. Together, this work provides a foundation for understanding a fundamental yet unresolved aspect of coronavirus replication.

microbiology↗

bioRxiv2021

Birnaviridae virus factories show features of liquid-liquid phase separation, and are distinct from paracrystalline arrays of virions observed by electron microscopy

To gain more information about the nature of Birnaviridae virus factories (VFs), we used a recombinant infectious bursal disease virus (IBDV) expressing split-GFP11 tagged to the polymerase (VP1) that we have previously shown is a marker for VFs in infected cells expressing GFP1-10. We found that VFs co-localized with 5-ethynyl uridine in the presence of actinomycin D, confirming they were the site of de novo RNA synthesis, and VFs were visible in infected cells that were fixed and permeabilized with digitonin, demonstrating that they were not membrane bound. Fluorescence recovery after photobleaching (FRAP) a region of interest within the VFs occurred rapidly, recovering from approximately 25% to 87% the original intensity over 146 seconds, and VFs were dissolved by 1,6-hexanediol treatment, demonstrating they showed properties consistent with liquid-liquid phase separation. There was a lower co-localization of the VF GFP signal with the capsid protein VP2 (Manders coefficient (MC) 0.6), compared to VP3 (MC, 0.9), which prompted us to investigate the VF ultrastructure by transmission electron microscopy (TEM). In infected cells, paracrystalline arrays (PAs) of virions were observed in the cytoplasm, as well as discrete electron dense regions. Using correlative light and electron microscopy (CLEM), we observed that the electron dense regions correlated with the GFP signal of the VFs, which were distinct from the PAs. In summary, Birnaviridae VFs are sites of de novo RNA synthesis, are not bound by a membrane, show properties consistent with liquid-liquid phase separation, and are distinct from the PAs observed by TEM. ImportanceMembers of the Birnaviridae infect birds, fish and insects, and are responsible for diseases of significant economic importance to the poultry industry and aquaculture. Despite their importance, how they replicate in cells remains poorly understood. Here, we show that the Birnaviridae virus factories are not membrane bound, demonstrate properties consistent with liquid-liquid phase separation, and are distinct from the paracrystalline arrays of virions observed by transmission electron microscopy, enhancing our fundamental knowledge of virus replication that could be used to develop strategies to control disease, or optimize their therapeutic application.

microbiology↗

bioRxiv2021

Coronavirus RNA synthesis takes place within membrane-bound sites

Infectious bronchitis virus (IBV), a gammacoronavirus, is an economically important virus to the poultry industry as well as a significant welfare issue for chickens. As for all positive strand RNA viruses, IBV infection causes rearrangements of the host cell intracellular membranes to form replication organelles. Replication organelle formation is a highly conserved and vital step in the viral life cycle. Here, we investigate the localization of viral RNA synthesis and the link with replication organelles in host cells. We have shown that sites of viral RNA synthesis and virus-related dsRNA are associated with one another and, significantly, that they are located within a membrane-bound compartment within the cell. We have also shown that some viral RNA produced early in infection remains within these membranes throughout infection. Importantly, we demonstrate conservation across all four coronavirus genera, including SARS-CoV-2. Under-standing more about the replication of these viruses is imperative in order to effectively find ways to control them.

microbiology↗

bioRxiv2020

Quantifying the acquisition and retention of lumpy skin disease virus by haematophagus insects and the implications for transmission and control.

Lumpy skin disease virus (LSDV), a poxvirus that causes severe disease in cattle, has in the last few years rapidly extended its distribution from Africa and the Middle East into Europe, Russia, and across Asia. LSDV is believed to be primarily spread mechanically by blood-feeding arthropods, however the exact mode of arthropod transmission, the relative ability of different arthropod species to acquire and retain the virus, as well as their comparative importance for LSDV transmission, remain poorly characterised. Since the vector-borne nature of LSDV transmission is believed to have enabled the rapid geographic expansion of this virus, the lack of quantitative evidence on LSDV transmission has impeded effective control of the disease during the current epidemic. Obtaining high quality data on virus transmission by arthropods is challenging, and practical limitations often result in inadequate arthropod numbers or model hosts, limiting the transferability of experimental findings to the natural transmission scenario. We have addressed these limitations in this study. Using a highly representative bovine experimental model of lumpy skin disease we allowed four representative vector species (Aedes aegypti, Culex quinquefasciatus, Stomoxys calcitrans and Culicoides nubeculosus) to blood-feed on LSDV-inoculated cattle in order to examine the acquisition and retention of LSDV by these species in unprecedented detail. We found the probability of LSDV transmission from clinical cattle to vector correlated with disease severity. Subclinical disease was more common than clinical disease in the inoculated cattle, however the probability of vectors acquiring LSDV from subclinical animals was very low. All four potential vector species studied had a similar rate of acquisition of LSDV after feeding on the host, but Aedes aegypti and Stomoxys calcitrans retained the virus for a longer time, up to 8 days. There was no evidence of virus replication in the vector, consistent with mechanical rather than biological transmission. The parameters obtained in the in-vivo transmission experiments subsequently enabled enhanced modelling approaches to determine the basic reproduction number of LSDV in cattle mediated by each of the insect species. This was highest for Stomoxys calcitrans (19.1), C. nubeculosus (7.4), and Ae. aegypti (2.4), surprisingly indicating these three species are all potentially efficient transmitters of LSDV. These results reveal that currently applied LSDV control measures such as stamping out of all cattle on affected premises or insect control measures targeting single species need to be urgently reconsidered. Overall our studies have highlighted that the combination of highly relevant in-vivo experiments and mathematical modelling can be directly applied to devise evidence-based proportionate and targeted control programmes.

microbiology↗

bioRxiv2019

Discrete virus factories form in the cytoplasm of cells co-infected with two strains of the segmented dsRNA virus, infectious bursal disease virus (IBDV), that subsequently coalesce

The Birnaviridae family, responsible for major economic losses to poultry and aquaculture, are non-enveloped viruses with a segmented double-stranded (ds)RNA genome that replicate in discrete cytoplasmic virus factories (VFs). Reassortment is common, however, the underlying mechanism remains unknown given that VFs may act as a barrier to genome mixing. In order to provide new information on VF trafficking during dsRNA virus co-infection, we rescued two recombinant infectious bursal disease viruses (IBDVs) of strain PBG98 containing either a split GFP11- or Tetracysteine (TC)- tag fused to the VP1 polymerase (PBG98-VP1-GFP11 and PBG98-VP1-TC). DF-1 cells transfected with GFP1-10 prior to PBG98-VP1-GFP11 infection, or stained with ReAsH following PBG98-VP1-TC infection, had green or red foci in the cytoplasm respectively that co-localised with VP3 and dsRNA, consistent with VFs. The average number of VFs decreased from a mean of 60 to 5 per cell between 10 and 24 hours post infection (hpi) (p<0.001), while the average area increased from 1.24 m2 to 45.01m2 (p<0.001), and live cell imaging revealed that the VFs were highly dynamic structures that coalesced in the cytoplasm. Small VFs moved faster than large (average 0.57m/s at 16 hpi compared to 0.22 m/s at 22 hpi), and VF coalescence was dependent on an intact microtubule network and actin cytoskeleton. During co-infection with PBG98-VP1-GFP11 and PBG98-VP1-TC viruses, discrete VFs initially formed from each input virus that subsequently coalesced 10-16 hours post-infection. We speculate that dsRNA virus reassortment requires VF coalescence, and the potential for reassortment increases at later time points in infection. ImportanceReassortment is common in viruses with segmented double stranded (ds)RNA genomes. However, these viruses typically replicate within discrete cytoplasmic virus factories (VFs) that may represent a barrier to genome mixing. We generated the first replication competent tagged reporter birnaviruses, infectious bursal disease viruses (IBDVs) containing a split GFP11 or tetracysteine (TC) tag and used the viruses to track the location and movement of IBDV VFs, in order to better understand the intracellular dynamics of VFs from two different strains of dsRNA virus during a co-infection. Discrete VFs initially formed from each virus that subsequently coalesced from 10 hours pi. We hypothesise that VF coalescence is required for the reassortment of dsRNA viruses and the potential for reassortment increases later in the replication cycle. This study provides new information that adds to our understanding of dsRNA virus VF trafficking.

microbiology↗

bioRxiv2019

The porcine deltacoronavirus replication organelle comprises double membrane vesicles and zippered endoplasmic reticulum with double membrane spherules

Porcine deltacoronavirus (PDCoV) was first identified in Hong Kong in 2012 from samples taken from pigs in 2009. PDCoV was subsequently identified in the USA in 2014 in pigs with a history of severe diarrhea and the virus has now been detected in pigs in several countries around the world. Following the development of tissue culture adapted strains of PDCoV, it is now possible to begin to address questions regarding virus-host cell interactions for this genera of coronavirus. Here we present a detailed study of PDCoV induced replication organelles. All positive strand RNA viruses induce the rearrangement of cellular membranes during virus replication to support viral RNA synthesis, forming the replication organelle. Replication organelles for the Alpha-, Beta- and Gammacoronavirus genera have been characterized. However the structures induced by deltacoronaviruses, in particular the presence of convoluted membranes or double membrane spherules, are unknown. Initially, the dynamics of PDCoV strain OH-FD22 replication were assessed with the onset of viral RNA synthesis, protein synthesis and progeny particle release determined. Subsequently, virus induced membrane rearrangements were identified in infected cells by electron microscopy. As has been observed for all other coronaviruses studied to date, PDCoV replication was found to induce the formation of double membrane vesicles. Significantly however, PDCoV replication was also found to induce the formation of regions of zippered endoplasmic reticulum and small associated tethered vesicles, double membrane spherules. These structures strongly resemble the replication organelle induced by avian Gammacoronavirus infectious bronchitis virus.

microbiology↗