Visualizing the ribonucleoprotein content of single bunyavirus virions reveals more efficient genome packaging in the arthropod host

Abstract

Bunyaviruses have a genome that is divided over multiple segments. Genome segmentation complicates the generation of progeny virus, since each newly formed virus particle should preferably contain a full set of genome segments in order to disseminate efficiently within and between hosts. Here, we combine immunofluorescence and fluorescence in situ hybridization techniques to simultaneously visualize bunyavirus progeny virions and their genomic content at single-molecule resolution in the context of singly infected cells. Using Rift Valley fever virus and Schmallenberg virus as prototype tri-segmented bunyaviruses, we show that bunyavirus genome packaging is influenced by the intracellular viral genome content of individual cells, which results in greatly variable packaging efficiencies within a cell population. We further show that bunyavirus genome packaging is more efficient in insect cells compared to mammalian cells and provide new insights on the possibility that incomplete particles may contribute to bunyavirus spread as well.

Time-Resolved Analysis of N-RNA Interactions during RVFV Infection Shows Qualitative and Quantitative Shifts in RNA Encapsidation and Packaging

“…Unlike other segmented RNA viruses, RVFV appears not to form supramolecular RNA complexes consisting of the three genomic segments during infection [19]. Moreover, genome packaging efficiency (i.e., the proportion of virus particles that are fully infectious) depends on cell type; arthropod cells, such as C6/36, show more efficient packaging than that of mammalian cells, like VeroE6 [21]. Furthermore, packaging genomic RNAs enhances the release of viral particles, suggesting the presence of a quality-control or surveillance mechanism [11].…”

Hantavirus Replication Cycle—An Updated Structural Virology Perspective

“…After viral genome replication and transcription, the newly synthesized proteins and viral genomes have to be assembled to form new virions. Whether the genome segments are specifically recruited, as seen in influenza viruses [ 125 ], or packaged by statistical likelihood, as proposed for RVFV [ 126 , 127 ], is currently unknown. The cytoplasmic tail of Gc seems to be important for the recruitment of viral genomes into budding virions via an interaction with N [ 115 ].…”

Heterogeneity of Rift Valley fever virus transmission potential across livestock hosts, quantified through a model-based analysis of host viral load and vector infection

“…Indeed, once correlation between parameters are taken into account, the replication process is most different between severe and moderate infection within sheep and less so between host species. The model could be refined by incorporating an explicit immune response (Elliott and Weber, 2009;Mapder et al, 2019) or taking into account the genomic composition of viral particles (Jacobs et al, 2019;Bermúdez-Méndez et al, 2021), but the quantity of information needed (number of timesteps and replicates, inclusion of data on immune responses ) could hamper this costly data collection.…”

“…Further experiments are needed to know whether a given infectious titer sampled during the increasing or the decreasing phase of viral dynamics would yield the same probability to infect vectors. This comes down to defining what makes a viral particle infectious to host cells vs vector cells, and might relate to the efficiency of genome packaging by those cells (Bermúdez-Méndez et al, 2021). Mechanistic modeling will help grasp the complexity of involved processes.…”