Evolutionary analysis of V protein pseudogenization in an RNA editing-deficient paramyxovirus

This study investigated the evolutionary consequences of RNA editing loss in human parainfluenza virus type 1 (HPIV-1) by analyzing the pseudogenization of the V protein–coding region within the P gene. The authors performed a comprehensive comparative genomic analysis using 240 full-length HPIV-1 P gene sequences and defined a pseudo-V reading frame by virtually inserting a nucleotide at the conserved RNA editing site, using Sendai virus as a reference. They observed a markedly elevated and non-random accumulation of stop codons within the 253-amino-acid pseudo-V region, with highly conserved positions across strains, indicating strong evolutionary fixation. Comparative analyses across other viral genes and with Sendai virus demonstrated that this enrichment was specific to the HPIV-1 P gene. Furthermore, in silico evolutionary simulations showed that such stop codon accumulation could not be explained solely by constraints acting on the primary open reading frame. Overall, the study demonstrates that the loss of RNA editing in HPIV-1 has driven lineage-specific pseudogenization of the V protein region, providing new insights into the evolution of overlapping gene architectures and functional gene loss in paramyxoviruses.
(TMR)

Recovery of Infectious Oz Virus From Cloned cDNA

This study established a reverse genetics system for Oz virus (OZV), a recently identified tick-borne orthomyxovirus associated with a fatal human case in Japan. The authors constructed six plasmids encoding the full-length viral genome segments along with four helper plasmids expressing essential polymerase proteins (NP, PA, PB1, and PB2), and co-transfected them into BHK/T7-9 cells to recover infectious virus. They successfully generated recombinant OZV (rOZV), which induced cytopathic effects in cocultured cells and produced high viral titers comparable to wild-type virus. Growth kinetics analysis in Vero cells showed that rOZV replicated similarly to the wild-type strain, confirming the functional integrity of the rescued virus. The study also demonstrated that all genome segments and polymerase components are required for virus recovery, and that the chosen cell system significantly improves efficiency. Overall, this work provides a robust platform for studying OZV replication, pathogenicity, and for future development of antiviral strategies.
(TMR)

Heterozygous and generalist MxA super-restrictors overcome breadth-specificity trade-offs in antiviral restriction

This study investigated how the antiviral protein MxA evolves to restrict different viruses and overcome limitations in its activity. The authors used combinatorial mutagenesis of the MxA L4 loop to generate variants and tested their ability to block H5N1 influenza and Thogoto virus (THOV). They found that some mutations created “super-restrictor” variants with much stronger antiviral activity than the normal (wild-type) MxA. However, most of these variants showed a trade-off, meaning improved restriction of one virus reduced activity against another. A key finding was that a single amino acid (position 561) largely determines this trade-off: different residues favor restriction of different viruses. Despite this limitation, rare “generalist” variants were identified that can effectively restrict both viruses. Importantly, the study showed two ways to overcome this trade-off: either evolving generalist variants or combining different specialist variants in heterozygous form, which together provide broad antiviral protection. Overall, this work reveals how host antiviral proteins adapt and suggests strategies to enhance broad-spectrum viral restriction.
(TMR)

Sialic acids are a barrier to the entry of non-influenza orthomyxoviruses

This study explored how cell surface sialic acids (SAs) influence the entry of thogoto- and quaranjaviruses, a group of non-influenza orthomyxoviruses. Using pseudotyped vesicular stomatitis virus (VSV) and lentiviral systems expressing viral glycoproteins, alongside authentic Thogoto (THOV) and Dhori (DHOV) viruses, the authors evaluated viral entry under conditions of altered SA availability. Enzymatic removal of SAs or their masking with lectins consistently enhanced viral entry, in sharp contrast to influenza viruses, where SAs serve as essential receptors. Further analyses across multiple cell lines revealed an inverse relationship between SA abundance and viral entry efficiency, indicating that SAs act as inhibitory factors rather than facilitators. These findings were corroborated in primary human airway epithelial cells and with infectious virus assays, where depletion of SAs significantly increased viral replication. In addition, adaptive mutations identified through experimental evolution partially mitigated this restriction, suggesting that viral glycoproteins can evolve to counteract SA-mediated inhibition. Overall, the study uncovers a distinct entry mechanism for these viruses and highlights sialic acids as a natural barrier to infection, offering new insights into host restriction, viral adaptation, and transmission dynamics.
(TMR)