Biology subjects

Le Sage, V.

Publications and source records attributed to Le Sage, V..

18 recordsLinked to original sources

bioRxiv2026

Disruption of a CCR5-like immunoglobulin gene is linked to plague susceptibility in black-footed ferrets

Black-footed ferrets (Mustela nigripes) are among the worlds most endangered mammals and remain highly vulnerable to sylvatic plague caused by Yersinia pestis, yet the genetic basis of this susceptibility has remained unknown. Current conservation strategies rely on vaccination of captive-bred animals and large-scale flea control with insecticides, approaches that are costly, labor-intensive, and difficult to implement across the species natural range. Several closely related mustelid species, including the domestic ferret, are substantially more resistant to plague, providing an opportunity to identify naturally evolved immune mechanisms through comparative immunogenomics. Here we identify a conserved class of immunoglobulin lambda variable genes encoding unusually long antigen-binding loops with CCR5-mimicking sequence features that are widespread among Caniformia species. Because CCR5 has been implicated in host interactions with Yersinia species, we hypothesized that antibodies encoded by these germline genes contribute to plague resistance through receptor-like molecular mimicry. Consistent with this hypothesis, we show that these genes are under strong purifying selection in mustelids, are actively expressed in antibody repertoires, and monoclonal antibodies encoded by them reduced intracellular Y. pestis survival in macrophages. In contrast, all analyzed black-footed ferrets carried a frameshifting deletion resulting in loss of gene expression. These findings identify a naturally disrupted germline antibody gene as a candidate determinant of plague susceptibility in black-footed ferrets, demonstrating that variation in germline immunoglobulin genes can influence susceptibility to a lethal infectious disease. Ultimately, these findings lay the groundwork for genetically informed conservation management and the development of new antibody-based anti-plague strategies. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/734856v2_ufig1.gif" ALT="Figure 1"> View larger version (60K): org.highwire.dtl.DTLVardef@19d8ac1org.highwire.dtl.DTLVardef@a37aorg.highwire.dtl.DTLVardef@1ecd1e0org.highwire.dtl.DTLVardef@c6fd67_HPS_FORMAT_FIGEXP M_FIG C_FIG

immunology↗

bioRxiv2026

Variable transmission efficiency of mammalian origin HPAI D1.1 H5N1 strains in ferrets

Highly pathogenic avian influenza H5N1 2.3.4.4b genotype D1.1 lineage continues to predominate in the United States wild bird population and has spilled over into dairy cattle three independent times. To assess the transmission risk of this sublineage, we performed direct-contact transmission experiments for three distinct D1.1 strains in ferrets. Two of these strains were isolated from humans and one from a lethal cat infection. We found that only one human isolate (A/NV/10/2025) was able to transmit efficiently between ferrets. Compared to the other strains, this isolate harbored the mammalian adaptive PB2 D701N mutation, suggesting this mutation may be critical for D1.1 transmission as opposed to the PB2 E627K substitution present in the lethal cat isolate. Based on these data we conclude that the transmission fitness of D1.1 strains is modest but that special attention should be paid to emergence of adaptation at the PB2 701 position.

microbiology↗

bioRxiv2026

Within-host adaptive evolution is limited by genetic drift in experimental human influenza A virus infections

Selection of advantageous mutations drives the emergence of dominant variants during seasonal influenza epidemics. However, within-host detection of such variants remains rare, limiting our understanding of how selection operates at the scale of individual hosts. In this study, we used a controlled human infection model to examine the within-host evolutionary dynamics in thirteen participants intranasally infected with a seasonal H3N2 influenza A virus. Although this clinical trial is ongoing, our work represents a pre-planned, interim, exploratory analysis. Results in this system were contrasted with those observed in a ferret model of infection. The inoculum, used in both humans and ferrets, carried standing diversity that enabled evaluation of variant trajectories during infection. Although the dynamics were variable among participants, in humans, the minor variants in the PA and NP gene segments tended to increase in frequency as infection progressed. Variant dynamics were more consistent among ferrets but showed differences from humans in the fate of the minor NP allele. Based on these observations, we fit a population genetic model to longitudinal measurements of variant frequencies. Estimates of variant selection coefficients and effective viral population sizes indicated that in humans the two minor variants had a selective advantage over the major variants, but genetic drift was strong, limiting the efficiency of selection. In ferrets, the PA minor variant also was estimated to have a selective advantage, while the NP minor variant was estimated to have a selective disadvantage. Moreover, effective viral population sizes were estimated to be considerably higher in ferrets than in humans, indicating that genetic drift was weaker in ferrets. Our analyses reveal differing selective environments acting on influenza viruses in human and ferret hosts and indicate that selection at the within-host level is weakened by genetic drift.

microbiology↗

bioRxiv2025

Fatal Human H3N8 Influenza Virus has a Moderate Pandemic Risk

In China, low pathogenic avian influenza (LPAI) H3N8 virus is widespread among chickens and has recently caused three zoonotic infections, with the last one in 2023 being fatal. Here we evaluated the relative pandemic risk of this 2023 zoonotic H3N8 influenza virus, utilizing our previously published decision tree. Serological analysis indicated that a large proportion of the human population does not have any cross-neutralizing antibodies against this H3N8 strain. LPAI H3N8 displayed a dual affinity for 2-3 and 2-6 sialic acids and replicated efficiently in human bronchial epithelial cells. Furthermore, we observed H3N8 transmission via direct contact but not aerosols to ferrets with pre-existing H3N2 immunity. Although pre-existing H3N2 immunity resulted in a shortened disease course in ferrets, it did not reduce disease severity or replication in the respiratory tract. This study suggests that this zoonotic H3N8 strain has moderate pandemic potential and emphasizes the continued need for avian influenza surveillance.

microbiology↗

bioRxiv2024

Structural Convergence and Water-Mediated Substrate Mimicry Enable Broad Neuraminidase Inhibition by Human Antibodies

Influenza has been responsible for multiple global pandemics and seasonal epidemics and claimed millions of lives. The imminent threat of a panzootic outbreak of avian influenza H5N1 virus underscores the urgent need for pandemic preparedness and effective countermeasures, including monoclonal antibodies (mAbs). Here, we characterize human mAbs that target the highly conserved catalytic site of viral neuraminidase (NA), termed NCS mAbs, and the molecular basis of their broad specificity. Cross-reactive NA-specific B cells were isolated by using stabilized NA probes of non-circulating subtypes. We found that NCS mAbs recognized multiple NAs of influenza A as well as influenza B NAs and conferred prophylactic protections in mice against H1N1, H5N1, and influenza B viruses. Cryo-electron microscopy structures of two NCS mAbs revealed that they rely on structural mimicry of sialic acid, the substrate of NA, by coordinating not only amino acid side chains but also water molecules, enabling inhibition of NA activity across multiple influenza A and B viruses, including avian influenza H5N1 clade 2.3.4.4b viruses. Our results provide a molecular basis for the broad reactivity and inhibitory activity of NCS mAbs targeting the catalytic site of NA through substrate mimicry.

immunology↗

bioRxiv2024

Pre-existing H1N1 immunity reduces severe disease with bovine H5N1 influenza virus

The emergence of highly pathogenic H5N1 avian influenza in dairy cattle herds across the United States has caused multiple mild human infections. There is an urgent need to understand the risk of spillover into humans. Here, we show that pre-existing immunity from the 2009 H1N1 pandemic influenza virus provided protection from mortality and severe clinical disease to ferrets intranasally infected with bovine H5N1. H1N1 immune ferrets exhibited a differential tissue tropism with little bovine H5N1 viral dissemination to organs outside the respiratory tract and significantly less H5N1 virus found in nasal secretions and the respiratory tract. Additionally, ferrets with H1N1 prior immunity produced antibodies that cross-reacted with H5N1 neuraminidase protein. Taken together, these results suggest that mild disease in humans may be linked to prior immunity to human seasonal influenza viruses.

microbiology↗

bioRxiv2024

Disruption of Herpes Simplex Virus Type 2 pUL21 Phosphorylation Impairs Secondary Envelopment of Cytoplasmic Nucleocapsids

The multifunctional tegument protein pUL21 of HSV-2 is phosphorylated in infected cells. We have identified two residues in the unstructured linker region of pUL21, serine 251 and serine 253, as sites of phosphorylation. Both phosphorylation sites are absent in HSV-1 pUL21, which likely explains why phosphorylated pUL21 was not detected in cells infected with HSV-1. Cells infected with HSV-2 strain 186 viruses deficient in pUL21 phosphorylation exhibited reductions in both cell-cell spread of virus infection and virus replication. Defects in secondary envelopment of cytoplasmic nucleocapsids were also observed in cells infected with viruses deficient in pUL21 phosphorylation as well as in cells infected with multiple strains of HSV-2 and HSV-1 deleted for pUL21. These results confirm a role for HSV pUL21 in the secondary envelopment of cytoplasmic nucleocapsids and indicate that phosphorylation of HSV-2 pUL21 is required for this activity. Phosphorylation of pUL21 was not detected in cells infected with HSV-2 strain 186 mutants lacking the viral serine/threonine kinase pUL13, indicating a requirement for pUL13 in pUL21 phosphorylation. ImportanceIt is well known that post-translational modification of proteins by phosphorylation can regulate protein function. Here, we determined that phosphorylation of the multifunctional HSV-2 tegument protein pUL21 requires the viral serine/threonine kinase pUL13. Additionally, we identified serine residues within HSV-2 pUL21 that can be phosphorylated. Phenotypic analysis of mutant HSV-2 strains with deficiencies in pUL21 phosphorylation revealed reductions in both cell-cell spread of virus infection and virus replication. Deficiencies in pUL21 phosphorylation also compromised secondary envelopment of cytoplasmic nucleocapsids, a critical final step in the maturation of all herpes virions. Unlike HSV-2 pUL21, phosphorylation of HSV-1 pUL21 was not detected. This fundamental difference between HSV-2 and HSV-1 may underlie our previous observations that the requirements for pUL21 differ between HSV species.

microbiology↗

bioRxiv2024

Potential pandemic risk of circulating swine H1N2 influenza viruses

Influenza A viruses in swine have considerable genetic diversity and continue to pose a pandemic threat to humans. They were the source of the most recent influenza pandemic, and since 2010, novel swine viruses have spilled over into humans more than 400 times in the United States. Although these zoonotic infections generally result in mild illness with limited onward human transmission, the potential for sustained transmission of an emerging influenza virus between individuals due to lack of population level immunity is of great concern. Compiling the literature on pandemic threat assessment, we established a pipeline to characterize and triage influenza viruses for their pandemic risk and examined the pandemic potential of two widespread swine origin viruses. Our analysis revealed that a panel of human sera collected from healthy adults in 2020 has no cross-reactive neutralizing antibodies against an -H1 clade strain but do against a {gamma}-H1 clade strain. Swine H1N2 virus from the -H1 clade (-swH1N2) replicated efficiently in human airway cultures and exhibited phenotypic signatures similar to the human H1N1 pandemic strain from 2009 (H1N1pdm09). Furthermore, -swH1N2 was capable of efficient airborne transmission to both naive ferrets and ferrets with prior seasonal influenza immunity. Ferrets with H1N1pdm09 pre-existing immunity had reduced -swH1N2 viral shedding from the upper respiratory tract and cleared the infection faster. Despite this, H1N1pdm09-immune ferrets that became infected via the air could still onward transmit -swH1N2 with an efficiency of 50%. Taken together, these results indicate that this -swH1N2 strain has a higher pandemic potential, but a moderate level of impact since there is reduced replication fitness in animals with prior immunity.

microbiology↗

bioRxiv2023

Ventilation does not affect influenza virus transmission efficiency in a ferret playpen setup

Sustained community spread of influenza viruses relies on efficient person-to-person transmission. Current experimental transmission systems do not mimic environmental conditions (e.g., air exchange rates, flow patterns), host behaviors or exposure durations relevant to real-world settings. Therefore, results from these traditional systems may not be representative of influenza virus transmission in humans. To address this pitfall, we developed a modified, more realistic transmission setup and used it to investigate the impact of ventilation rates on transmission in a close-range, play-based scenario. In this setup, four immunologically naive recipient ferrets were exposed to a donor ferret infected with a genetically barcoded 2009 H1N1 virus (H1N1pdm09) for four hours. The ferrets interacted in a shared space that included toys, similar to a child care setting. The transmission efficiency was determined under conditions of low and high ventilation rates; air exchange rates of [~] 1.3 hr-1 and 23 hr-1, respectively. Despite the large difference in ventilation rate, transmission efficiency was the same, 50% in two independent replicate studies. The presence of infectious virus or viral RNA on surfaces and in air throughout the exposure area was similar regardless of ventilation rate. While high viral genetic diversity in donor ferret nasal washes was maintained during infection, recipient ferret nasal washes displayed low diversity, revealing a narrow transmission bottleneck regardless of ventilation rate. Our findings indicate that in exposures characterized by frequent close-range, play-based interactions and the presence of fomites, ventilation does not significantly impact transmission efficiency. SignificanceImproved ventilation in building has the potential to reduce transmission of respiratory viruses, but its effect in different settings is not well understood. We developed a novel system to study influenza virus transmission in the ferret animal model in an environment that mimics a child care center. We demonstrate that increased ventilation is not effective at disrupting transmission in this setting, suggesting that transmission occurs mainly at close-range or via fomites. Multiple interventions are needed to reduce the spread of influenza virus in this type of setting.

microbiology↗

bioRxiv2023

A broad antibody class engages the influenza virus hemagglutinin head at its stem interface

Influenza infection and vaccination impart strain-specific immunity that protects against neither seasonal antigenic variants nor the next pandemic. However, antibodies directed to conserved sites can confer broad protection. Here we identify and characterize a class of human antibodies that engage a previously undescribed, conserved epitope on the influenza hemagglutinin (HA) protein. Prototype antibody S8V1-157 binds at the normally occluded interface between the HA head and stem. Antibodies to this HA head-stem interface epitope are non-neutralizing in vitro but protect against lethal influenza infection in mice. Antibody isotypes that direct clearance of infected cells enhance this protection. Head-stem interface antibodies bind to most influenza A serotypes and seasonal human variants, and are present at low frequencies in the memory B cell populations of multiple human donors. Vaccines designed to elicit these antibodies might contribute to "universal" influenza immunity.

microbiology↗

bioRxiv2023

Influenza infected macrophages release viral ribonucleoproteins that shape the local host response

Airway epithelial cells and macrophages (M{Phi}) represent cellular targets of infection by influenza A virus (IAV). Epithelial cells support IAV infection and replication by enabling the generation and release of new viral particles (productive replication). In contrast, M{Phi} are susceptible to initial IAV infection but the release of infectious viral particles is inhibited through abortive replication. Despite the lack of infectious virions released from infected M{Phi}, we detected newly synthesised viral RNA and nucleoprotein (NP) in M{Phi} supernatants. We show that viral RNA is released from infected M{Phi} as viral ribonucleoprotein (vRNP) complexes which elicits potent inflammatory responses when exposed to uninfected cells. These vRNPs specifically induced IL-1{beta}, CXCL13, IL-32, CCL4 and CXCL10 in uninfected cells and were at least partially sensed through the RIG-I/MDA5 pathway. While M{Phi} represent a dead-end for IAV infection through abortive replication, the release of vRNPs shapes immune repsonses of uninfected cells in the local microenvironment.

microbiology↗

bioRxiv2023

Detection of Influenza virus and Streptococcus pneumoniae in air sampled from co-infected ferrets and analysis of their influence on pathogen stability

Secondary infection with Streptococcus pneumoniae has contributed significantly to morbidity and mortality during multiple influenza virus pandemics and remains a common threat today. During a concurrent infection, both pathogens can influence the transmission of each other, but the mechanisms behind this are unclear. In this study, condensation air sampling and cyclone bioaerosol sampling were performed using ferrets first infected with the 2009 H1N1 pandemic influenza virus (H1N1pdm09) and secondarily infected with S. pneumoniae strain D39 (Spn). We detected viable pathogens and microbial nucleic acid in expelled aerosols from co-infected ferrets, suggesting that these microbes could be present in the same respiratory expulsions. To assess whether microbial communities impact pathogen stability within an expelled droplet, we performed experiments measuring viral and bacterial persistence in 1 L droplets. We observed that H1N1pdm09 stability was unchanged in the presence of Spn. Further, Spn stability was moderately increased in the presence of H1N1pdm09, although the degree of stabilization differed between airways surface liquid collected from individual patient cultures. These findings are the first to collect both pathogens from the air and in doing so, they provide insight into the interplay between these pathogens and their hosts. ImportanceThe impact of microbial communities on transmission fitness and environmental persistence is under-studied. Environmental stability of microbes is crucial to identifying transmission risks and mitigation strategies, such as removal of contaminated aerosols and decontamination of surfaces. Co-infection with S. pneumoniae is very common during influenza virus infection, but little work has been done to understand whether S. pneumoniae alters stability of influenza virus, or vice versa, in a relevant system. Here, we demonstrate that influenza virus and S. pneumoniae are expelled by co-infected hosts. Our stability assays did not reveal any impact of S. pneumoniae on influenza virus stability, and a trend towards increased stability of S. pneumoniae in the presence of influenza viruses. Future work characterizing environmental persistence of viruses and bacteria should include microbially-complex solutions to better mimic physiologically relevant conditions.

microbiology↗

bioRxiv2022

Robustness of the ferret model for influenza risk assessment studies: a cross-laboratory exercise

Ferrets represent the preferred animal model for assessing the transmission potential of newly emerged zoonotic influenza viruses. However, heterogeneity among established experimental protocols and facilities across different laboratories may lead to variable results, complicating interpretation of transmission experimental data. Between 2018-2020, a global exercise was conducted by 11 participating laboratories to assess the range of variation in ferret transmission experiments using two common stock H1N1 influenza viruses that possess different transmission characteristics in ferrets. Inoculation route, dose, and volume were standardized, and all participating laboratories followed the same experimental conditions for respiratory droplet transmission, including a strict 1:1 donor:contact ratio. Additional host and environmental parameters likely to affect influenza transmission kinetics were monitored throughout. Overall transmission outcomes for both viruses across 11 laboratories were concordant, suggesting the robustness of the ferret model for zoonotic influenza risk assessment. To attain high confidence in identifying zoonotic influenza viruses with moderate-to-high or low transmissibility, our analyses support that as few as three but as many as five laboratories, respectively, would need to independently perform viral transmission experiments with concordant results. This exercise facilitates the development of a more homogenous protocol for ferret transmission experiments that are employed for the purposes of risk assessment.

microbiology↗

bioRxiv2021

Parallel evolution between genomic segments of seasonal human influenza viruses reveals RNA-RNA relationships

The influenza A virus (IAV) genome consists of eight negative-sense viral RNA (vRNA) segments that are selectively assembled into progeny virus particles through RNA-RNA interactions. To identify relationships between vRNA segments, we examined parallel evolution between vRNA segments of seasonal human IAV, finding that evolutionary relationships between vRNA segments differ between subtypes and antigenically-shifted strains. Intersegmental relationships were distinct between H3N2 and H1N1 viruses, but largely conserved over time in H3N2 viruses. However, parallel evolution of vRNA segments diverged between H1N1 strains isolated before and after the 2009 pandemic. Surprisingly, intersegmental relationships were not driven solely by protein sequence, which is potentially indicative of RNA-RNA driven coevolution. Colocalization of highly coevolved vRNA segments was enriched over other pairs at the nuclear periphery during a productive viral infection. This study illustrates how phylogenetics can be applied to interrogate putative RNA interactions underlying selective assembly of IAV.

microbiology↗

bioRxiv2020

Coinfection of Streptococcus pneumoniae reduces airborne transmission of influenza virus

Secondary bacterial infection, especially with Streptococcus pneumoniae (Spn), is a common complication in fatal and ICU cases of influenza virus infection. During the H1N1 pandemic of 2009 (H1N1pdm09), there was higher mortality in healthy young adults due to secondary bacterial pneumonia, with Spn being the most frequent bacterial species. Previous studies in mice and ferrets have suggested a synergistic relationship between Spn and influenza viruses. In this study, we used the ferret model to study whether airborne transmission of H1N1pdm09 was influenced by coinfection with two Spn serotypes: type 2 (D39) and type 19F (BHN97). We found that coinfected animals experienced more severe clinical symptoms as well as increased bacterial colonization of the upper respiratory tract. In contrast, we observed that coinfection resulted in reduced airborne transmission of influenza virus. Only 1/3 animals coinfected with D39 transmitted H1N1pdm09 virus to a naive recipient compared to 3/3 transmission efficiency in animals infected with influenza virus alone. A similar trend was seen in coinfection with BHN97, suggesting that coinfection with Spn reduces influenza virus airborne transmission. The decrease in transmission does not appear to be caused by decreased stability of H1N1pdm09 in expelled droplets in the presence of Spn. Rather, coinfection resulted in decreased viral shedding in the ferret upper respiratory tract. Thus, we conclude that coinfection enhances colonization and airborne transmission of Spn but decreases replication and transmission of H1N1pdm09. Our data points to an asymmetrical relationship between these two pathogens rather than a synergistic one. SignificanceAirborne transmission of respiratory viruses is influenced by many host and environmental parameters. The complex interplay between bacterial and viral coinfections on transmission of respiratory viruses has been understudied. We demonstrate that coinfection with Streptococcus pneumoniae reduces airborne transmission of influenza A viruses by decreasing viral titers in the upper respiratory tract. Instead of implicating a synergistic relationship between bacteria and virus, our work demonstrates an asymmetric relationship where bacteria benefit from the virus but where the fitness of influenza A viruses is negatively impacted by coinfection. The implications of exploring how microbial communities can influence the fitness of pathogenic organisms is a novel avenue for transmission control of pandemic respiratory viruses.

microbiology↗

bioRxiv2020

Pre-existing immunity provides a barrier to airborne transmission of influenza viruses

Human-to-human transmission of influenza viruses is a serious public health threat, yet the precise role of immunity from previous infections on the susceptibility to airborne viruses is still unknown. Using human seasonal influenza viruses in a ferret model, we examined the roles of exposure duration and heterosubtypic immunity on influenza transmission. We found that airborne transmission of seasonal influenza strains is abrogated in recipient animals with pre-existing non-neutralizing immunity, indicating that transmissibility of a given influenza virus strain should be examined in the context of ferrets that are not immunologically naive.

microbiology↗

bioRxiv2020

Differentiating the Roles of UL16, UL21 and Us3 in the Nuclear Egress of Herpes Simplex Virus Capsids

Previous studies from our laboratory established that pUL16 and pUL21 are required for efficient nuclear egress of herpes simplex type 2 (HSV-2) capsids. To better understand the role of these proteins in nuclear egress, we wished to establish whether nuclear egress complex (NEC) localization and/or function was altered in the absence of either pUL16 or pUL21. We used antiserum raised against HSV-2 NEC components pUL31 and pUL34 to examine NEC localization by immunofluorescence microscopy. NEC localization in cells infected with pUL16 deficient viruses was indistinguishable from that observed in cells infected with wild type viruses. By contrast, NEC localization was found to be aberrant in cells infected with pUL21 deficient virus and, instead, showed some similarity to the aberrant NEC localization pattern observed in cells infected with pUs3 deficient virus. These results indicated that pUL16 plays a role in nuclear egress that is distinct from that of pUL21 and pUs3. Higher resolution examination of nuclear envelope ultrastructure in cells infected with pUL21 deficient viruses by transmission electron microscopy showed different types of nuclear envelope perturbations, including some that were not observed in cells infected with pUs3 deficient virus. The formation of the nuclear envelope perturbations observed in pUL21 deficient virus infections was found to be dependent on a functional NEC, revealing a novel role for pUL21 in regulating NEC activity. The results of comparisons of nuclear envelope ultrastructure in cells infected with viruses lacking pUs3, pUL16 or both pUs3 and pUL16 were consistent with a role for pUL16 upstream of primary capsid envelopment and shed new light on how pUs3 functions in nuclear egress. Author summaryThe membrane deformation activity of the herpesvirus nuclear egress complex (NEC), allows viral capsids to transit from their site of assembly in the nucleus through both nuclear membranes into the cytoplasm. The timing, extent and directionality of NEC activity must be precisely controlled during viral infection, yet our knowledge of how NEC activity is controlled is incomplete. To determine how pUL16 and pUL21, two viral proteins required for nuclear egress of herpes simplex virus type 2 (HSV-2) capsids, function to promote nuclear egress, we examined how the lack of each protein impacted NEC localization. These analyses revealed a function of pUL16 in nuclear egress that is distinct from that of pUL21, uncovered a novel role for pUL21 in regulating NEC activity and shed new light on how a viral kinase, pUs3, regulates nuclear egress. Nuclear egress of viral capsids is a common feature of the replicative cycle of all herpesviruses. A complete understanding of all aspects of nuclear egress, including how viral NEC activity is controlled, may yield strategies to disrupt this process that could be applied to the development of herpes-specific antiviral drugs.

microbiology↗

bioRxiv2019

Altered Nucleoprotein Binding to Influenza Virus RNA Impacts Packaging Efficiency and Replication

The genome of Influenza A viruses consists of eight negative-sense RNA segments that are bound by viral nucleoprotein (NP). We recently showed that NP binding is not uniform along the segments but exhibits regions of enrichment as well as depletion. Furthermore, genome-wide NP binding profiles are distinct even in strains with high sequence similarity, such as the two H1N1 strains A/WSN/1933 and A/California/07/2009. Here, we performed interstrain segment swapping experiments with segments of either high or low congruency in NP binding, which suggested that a segment with a similar overall NP binding profile preserved replication fitness of the resulting virus. Further sub-segmental swapping experiments demonstrated that NP binding is affected by changes to the underlying nucleotide sequence, as NP peaks can either become lost or appear de novo at mutated regions. Unexpectedly, these local nucleotide changes in one segment not only affect NP binding in cis, but also impact the genome-wide NP binding profile on other segments in a vRNA sequence-independent manner, suggesting that primary sequence alone is not the sole determinant for NP association to vRNA. Moreover, we observed that sub-segmental mutations that affect NP binding profiles can result in reduced replication fitness, which is caused by defects in vRNA packaging efficiency and an increase in semi-infectious particle production. Taken together, our results indicate that the pattern of NP binding to vRNA is important for efficient virus replication.\n\nAuthor SummaryEach viral RNA (vRNA) segment is bound by the polymerase complex at the 5' and 3' ends, while the remainder of the vRNA is coated non-uniformly and non-randomly by nucleoprotein (NP). To explore the constraints of NP binding to vRNA, we used high-throughput sequencing of RNA isolated by crosslinking immunoprecipitation (HITS-CLIP) of mutant H1N1 strains with exchanged vRNA sequences and observed that NP binding can be changed based on vRNA sequence. The most striking observation of our study is that nucleotide changes in one segment can have genome-wide effects on the NP binding profile of other segments. We refer to this phenomenon as the butterfly effect of influenza packaging. Our results provide an important context in which to consider future studies regarding influenza packaging and assembly.

microbiology↗