FAST Proteins: Development and Use of Reverse Genetics Systems for Reoviridae Viruses

Rapid production of recombinant rotaviruses by overexpression of NSP2 and NSP5 genes with modified nucleotide sequences

Reverse genetics systems for rotaviruses (RV) facilitate the generation of genetically engineered RVs by transfection of 11 plasmids encoding 11 genomic viral RNA segments. In addition to viral genome expression, overexpression of NSP2 and NSP5 has been used to increase the rescue efficiency of recombinant RVs. Here, we showed that the overexpression of nucleotide sequence-modified NSP2 and NSP5 enabled the rapid and efficient production of recombinant RVs. Using improved reverse genetics, we established a reverse genetics system for human and bovine RV clinical isolates, as well as laboratory strains of bovine RV (NCDV and UK) and porcine RV (Gottfried). In addition, we rescued low-replicating recombinant RVs carrying a mutant NSP4 lacking the double-layered particle-binding domain, which was deficient in the efficient production of mature virions. These advancements in reverse genetics enabled the generation of molecular clones of RV clinical isolates and recombinant RVs harboring critical amino acid mutations, offering a versatile platform for investigating RV biology and pathogenesis.IMPORTANCERecombinant rotavirus (RV) synthesis via reverse genetics relies on both the viral propagation capacity and the efficiency of the experimental system. Since the establishment of our reverse genetics system, several enhancements have been implemented to augment the rescue efficiency. Nevertheless, challenges persist in generating RV clinical strains and recombinant viruses with low replication capacities. Notably, this improved reverse genetics system successfully facilitated the establishment of molecular clones of human and bovine RV clinical isolates. Fecal samples from patients with RV typically harbor quasi-species or, occasionally, multiple genotypes of RV. In the present study, we performed the genetic sequencing of clinical viral strains during the early propagation stages in cultured cells. Subsequently, infectious viruses were synthesized, allowing the characterization of circulating viruses in nature. This approach provides valuable insights into the genetic diversity and dynamics of RV populations and contributes to a more comprehensive understanding of viral pathogenesis and evolution.

Avian deltacoronaviruses encode fusion-associated small transmembrane proteins that can induce syncytia formation

Fusion-associated small transmembrane (FAST) proteins are nonstructural viral proteins that induce cell-cell fusion. FAST proteins, which previously were identified in the genomes of double-stranded RNA viruses, typically contain an acylated N-terminal ectodomain, central transmembrane domain, and C-terminal endodomain with a polybasic region. Using sequence homology and protein motif prediction, we identified accessory proteins in a subset of avian deltacoronaviruses as putative FAST proteins. Transient expression of thrush coronavirus NS7b or common moorhen coronavirus NS7a, but not night heron coronavirus NS7b, induced cell-cell fusion. Syncytia were detected in primate kidney epithelial cells or fibroblasts but not chicken embryo fibroblasts, and addition of an N-terminal FLAG peptide to the proteins ablated fusion activity. These findings suggest that multiple avian deltacoronaviruses, positive-sense RNA viruses, encode nonstructural proteins that can mediate cell-cell fusion and share features with known FAST proteins. Additional studies are needed to understand contributions of these proteins to deltacoronavirus biology.

Identification, pathological, and genomic characterization of novel goose reovirus associated with liver necrosis in geese, China

Since 2021, a novel strain of goose reovirus (GRV) has emerged within the goose farming industry in Guangdong province, China. This particular viral variant is distinguished by the presence of white necrotic foci primarily localized in the liver and spleen, leading to substantial economic losses for the poultry industry. However, the etiology, prevalence and genomic characteristics of the causative agent have not been thoroughly investigated. In this study, we conducted an epidemiological inquiry employing suspected GRV samples collected from May 2021 to September 2022. The macroscopic pathological and histopathological lesions associated with GRV-infected clinical specimens were examined. Moreover, we successfully isolated the GRV strain and elucidated the complete genome sequence of the isolate GD21/88. Through phylogenetic and recombination analysis, we unveiled that the GRV strains represent a novel variant resulting from multiple reassortment events. Specifically, the μNS, λC, and σNS genes of GRV were found to have originated from chicken reovirus, while the σA gene of GRV exhibited a higher degree of similarity with a novel duck reovirus. The remaining genes of GRV were traced back to Muscovy duck reovirus. Collectively, our findings underscore the significance of GRV as a pathogenic agent impacting the goose farming industry. The insights gleaned from this study contribute to a more comprehensive understanding of the epidemiology of GRV in Southern China and shed light on the genetic reassortment events exhibited by the virus.

Genetic engineering strategy for generating a stable dsRNA virus vector using a virus-like codon-modified transgene

IMPORTANCE

The stabilities of transgenes in RNA virus vectors differ between the genes of interest, but the molecular mechanisms determining genetic stability remain unknown. This study demonstrated that the stability of a transgene was affected by the nucleotide composition, and altering the codon usage of transgenes to resemble that of the viral genome significantly increased transgene stability in double-stranded RNA virus vectors. The virus-like codon modification strategy enabled generation of stable rotavirus and mammalian orthoreovirus vectors, which could be developed as machinery for gene delivery to the intestines and/or respiratory organs. This technology has further potential to be expanded to other RNA viruses.

Rotavirus Particle Disassembly and Assembly In Vivo and In Vitro

Rotaviruses (RVs) are non-enveloped multilayered dsRNA viruses that are major etiologic agents of diarrheal disease in humans and in the young in a large number of animal species. The viral particle is composed of three different protein layers that enclose the segmented dsRNA genome and the transcriptional complexes. Each layer defines a unique subparticle that is associated with a different phase of the replication cycle. Thus, while single- and double-layered particles are associated with the intracellular processes of selective packaging, genome replication, and transcription, the viral machinery necessary for entry is located in the third layer. This modular nature of its particle allows rotaviruses to control its replication cycle by the disassembly and assembly of its structural proteins. In this review, we examine the significant advances in structural, molecular, and cellular RV biology that have contributed during the last few years to illuminating the intricate details of the RV particle disassembly and assembly processes.

Recent advances in Reovirales viruses reverse genetics research

Reovirales are segmented double-strand RNA viruses with a broad host range that pose a serious threat to human and animal health. However, there are numerous viral species within the Reovirales, some of which have lagged behind other RNA viruses in the study of their biology due to the lack of an effective reverse genetics (RG) system. The RG systems are the most powerful tools for studying viral protein function, viral gene expression regulation, viral pathogenesis, and the generation of engineered vaccines. Recently, several entirely plasmid-based RG systems have been developed for several members of the Reovirales. This review outlines the development and future direction of the RG system for the best studied Reovirales viruses.

Phylogenetic Diversity of Animal Oral and Gastrointestinal Viromes Useful in Surveillance of Zoonoses

Great emphasis has been placed on bacterial microbiomes in human and animal systems. In recent years, advances in metagenomics have allowed for the detection and characterization of more and more native viral particles also residing in these organisms. The digestive tracts of animals and humans—from the oral cavity, to the gut, to fecal excretions—have become one such area of interest. Next-generation sequencing and bioinformatic analyses have uncovered vast phylogenetic virome diversity in companion animals, such as dogs and cats, as well as farm animals and wildlife such as bats. Zoonotic and arthropod-borne illnesses remain major causes of worldwide outbreaks, as demonstrated by the devastating COVID-19 pandemic. This highlights the increasing need to identify and study animal viromes to prevent such disastrous cross-species transmission outbreaks in the coming years. Novel viruses have been uncovered in the viromes of multiple organisms, including birds, bats, cats, and dogs. Although the exact consequences for public health have not yet become clear, many analyses have revealed viromes dominated by RNA viruses, which can be the most problematic to human health, as these genomes are known for their high mutation rates and immune system evasion capabilities. Furthermore, in the wake of worldwide disruption from the COVID-19 pandemic, it is evident that proper surveillance of viral biodiversity is crucial. For instance, gut viral metagenomic analysis in dogs has shown close relationships between the highly abundant canine coronavirus and human coronavirus strains 229E and NL63. Future studies and vigilance could potentially save many lives.

Re-Examining Rotavirus Innate Immune Evasion: Potential Applications of the Reverse Genetics System

Rotaviruses represent one of the most successful pathogens in the world, with high infectivity and efficient transmission between the young of many animal species, including humans. To overcome host defenses, rotaviruses have evolved a plethora of strategies to effectively evade the innate immune response, establish initial infection in the small intestine, produce progeny, and shed into the environment. Previously, studying the roles and relative contributions of specific rotaviral factors in innate immune evasion had been challenging without a plasmid-only reverse genetics system. Although still in its infancy, current reverse genetics technology will help address important research questions regarding rotavirus innate immune evasion, host range restriction, and viral pathogenesis. In this review, we summarize the current knowledge about the antiviral host innate immune defense mechanisms, countermeasures of rotavirus-encoded factors, and strategies to better understand these interactions using the rotavirus reverse genetics system.