Biology subjects

Fros, J. J.

Publications and source records attributed to Fros, J. J..

4 recordsLinked to original sources

bioRxiv2026

Sequence Homology and Tissue Tropism Determine Superinfection Exclusion of Zika virus in Aedes aegypti Mediated by an insect-specific Binjari-Zika Virus Chimera

Arboviruses such as dengue, Zika, and chikungunya viruses cause widespread disease and continue to expand their geographical range due to climate change and vector spread. Insect-specific flaviviruses (ISFs) are promising biocontrol candidates of arboviruses, due to recent studies showing that prior infection with an ISF can reduce arbovirus replication in mosquitoes through superinfection exclusion (SIE). However, the route of infection, tissue tropism, pathogenesis and the mechanisms underlying SIE of ISFs in mosquitoes remain unclear. RNA interference (RNAi) is a potent antiviral response in insects, therefore it is expected that sequence homology between the ISF and the arbovirus will strengthen SIE. Here, we used ISF Binjari virus and a chimera containing the Zika virus structural proteins prME (BinJ-ZIKV) as a model system. Intrathoracic injection of BinJ-ZIKV in Aedes aegypti led to rapid systemic infection that excluded the midgut, subsequently blocking ZIKV dissemination from the midgut. SIE was strongest in tissues where primary-virus replication was highest. This spatial component of SIE was stronger when there was sequence homology between the ISF and arbovirus and displayed a strong 21nt siRNA response, suggesting RNAi contributed to the observed SIE. Upon oral inoculation, BinJ-ZIKV replicated efficiently in mosquitoes, was detected across multiple tissues, and saliva. BinJ-ZIKV also had higher infection establishment than BinJV at lower oral titres. SIE was observed for BinJ-ZIKV infection after oral exposure interfered with subsequent ZIKV midgut infection. Together, these findings support engineered ISF-chimeras as valuable experimental tools to dissect viral determinants of SIE and to optimize mosquito-based arbovirus interference strategies. ImportanceAnnually, over 400 million people are infected with mosquito-transmitted viruses. Insect-specific flaviviruses (ISFs) can interfere with the transmission of clinically important viruses through a phenomenon termed superinfection exclusion (SIE). However, the mechanisms of SIE remain poorly understood. Using a Binjari virus chimera expressing Zika virus (ZIKV) structural proteins, we show that SIE is highly tissue-specific, with exclusion of ZIKV only occurring at sites where the chimera actively replicates and induces the mosquito antiviral RNA interference pathway. We further demonstrate that incorporation of Zika virus prM and E proteins into the ISF backbone enhances infection of the mosquito midgut following oral exposure, which enables direct inhibition of ZIKV infection after a subsequent infectious blood meal. Together, these findings define a replication-dependent, tissue-specific mechanism of ISF-mediated protection and provide a framework for reducing mosquito-borne virus transmission through SIE.

microbiology↗

bioRxiv2025

The effect of increased CpG and UpA dinucleotides in the West Nile virus genome on virus transmission by Culex mosquitoes and pathogenesis in a vertebrate host

Vertebrate animals and many small DNA and single-stranded RNA viruses that infect vertebrates have evolved to suppress genomic CpG dinucleotides. All organisms and most viruses additionally suppress UpA dinucleotides in protein coding RNA. Synonymously recoding viral genomes to introduce CpG or UpA dinucleotides has emerged as an approach for viral attenuation and vaccine development. However, studies that investigate the effects of this recoding strategy on viral replication and pathogenesis in vivo are still limited. Flaviviruses including West Nile virus (WNV) are transmitted between vertebrate hosts by invertebrate vectors. In humans, WNV infection can cause flu-like symptoms and neuroinvasive disease. We investigated how alterations in WNV dinucleotide frequencies impact virus replication, transmission by vector mosquitoes, as well as pathogenesis and neuroinvasiveness in vertebrates. In Culex pipiens vector mosquitoes and Culex cell lines only WNV with elevated UpA frequencies displayed attenuated replication. In vertebrate cell lines and primary human neuro-astrocyte co-cultures both UpA and CpG enrichment reduced viral replication. In mice, the CpG-high WNV mutant demonstrated partial attenuation with delayed weight loss compared to wild-type WNV, though infection still resulted in 100% mortality. In contrast, 75% of animals survived inoculation with the UpA-high WNV mutant and were protected against wild-type WNV challenge. Notably, all animals that succumbed to infection had similar levels of virus in the brain, irrespective of the WNV mutant. Our results underscore the complex interplay between viral genome composition and host immune responses, highlighting potential safety concerns for dinucleotide manipulation as a strategy for live-attenuated vaccine development in flaviviruses. ImportanceFlaviviruses such as West Nile virus (WNV) pose significant public health concerns due to their potential to cause severe neurological disease. Synonymously recoding flavivirus genomes to introduce CpG or UpA dinucleotides has emerged as an approach for viral attenuation and vaccine development. However, the in vivo effects of manipulating these frequencies across the complete transmission cycle remained unexplored. Our study provides comprehensive insights of how CpG and UpA recoding affects WNV replication in both the mosquito vector and vertebrate hosts. We demonstrate that elevated UpA content attenuates virus replication throughout the transmission cycle, while CpG enrichment only impacts replication in the vertebrate host. Although UpA-high WNV shows significant attenuation and provides protection against wild-type infection, animals that succumb exhibit similar brain viral loads as wild-type infections. These findings have critical implications for live-attenuated vaccine development based on dinucleotide manipulation, specifically highlighting the importance of carefully evaluating the risk of neuroinvasion.

microbiology↗

bioRxiv2022

The virome of the invasive Asian bush mosquito Aedes japonicus in Europe

BackgroundThe Asian bush mosquito Aedes japonicus is rapidly invading North America and Europe. Due to its potential to transmit multiple pathogenic arthropod-borne (arbo)viruses including Zika virus, West Nile virus and chikungunya virus, it is important to understand the biology of this vector mosquito in more detail. In addition to arboviruses, mosquitoes can also carry insect-specific viruses that receive increasing attention due to their potential effects on host physiology and arbovirus transmission. In this study, we characterized the collection of viruses, referred to as the virome, circulating in Ae. japonicus populations in the Netherlands and France. ResultsApplying a small RNA-based metagenomic approach to Ae. japonicus, we uncovered a distinct group of viruses present in samples from both the Netherlands and France. These included one known virus, Ae. japonicus narnavirus 1 (AejapNV1), and three new virus species that we named Ae. japonicus totivirus 1 (AejapTV1), Ae. japonicus anphevirus 1 (AejapAV1) and Ae. japonicus bunyavirus 1 (AejapBV1). We also discovered sequences that were presumably derived from two additional novel viruses: Ae. japonicus bunyavirus 2 (AejapBV2) and Ae. japonicus rhabdovirus 1 (AejapRV1). All six viruses induced strong RNA interference responses, including the production of 21 nucleotide sized small interfering RNAs, a signature of active replication in the host. Notably, AejapBV1 and AejapBV2 belong to different viral families, however, no RNA-dependent RNA polymerase sequence has been found for AejapBV2. Intriguingly, our small RNA-based approach identified a [~]1 kb long ambigrammatic RNA that is associated with AejapNV1 as a secondary segment but showed no similarity to any sequence in public databases. We confirmed the presence of AejapNV1 primary and secondary segments, AejapTV1, AejapAV1 and AejapBV1 by reverse-transcriptase PCR in wild-caught Ae. japonicus mosquitoes. AejapNV1 and AejapTV1 were found at high prevalence (87-100%) in adult females, adult males and larvae. ConclusionsUsing a small RNA-based, sequence-independent metagenomic strategy, we uncovered a conserved and prevalent virome among Ae. japonicus mosquito populations. The high prevalence of AejapNV1 and AejapTV1 across all tested mosquito life stages suggests that these viruses are intimately associated with Ae. japonicus and may affect different aspects of the physiology of this vector mosquito.

microbiology↗

bioRxiv2021

An adaptive compromise - Conflicting evolutionary pressures on arthropod borne Zika virus dinucleotide composition in mammalian hosts and mosquito vectors

Most vertebrate RNA viruses show pervasive suppression of CpG and UpA dinucleotides, closely resembling the dinucleotide composition of host cell transcriptomes. In contrast, CpG suppression is absent in both invertebrate mRNA and RNA viruses that exclusively infect arthropods. Arthropod-borne (arbo) viruses are transmitted between vertebrate hosts by invertebrate vectors and thus encounter potentially conflicting evolutionary pressures in the different cytoplasmic environments. Using a newly developed Zika virus (ZIKV) model, we have investigated how demands for CpG suppression in vertebrate cells can be reconciled with potentially quite different compositional requirements in invertebrates, and how this affects ZIKV replication and transmission. Mutant viruses with synonymously elevated CpG or UpA dinucleotide frequencies showed attenuated replication in vertebrate cell lines, which was rescued by knockout of the zinc-finger antiviral protein (ZAP). Conversely, in mosquito cells, ZIKV mutants with elevated CpG dinucleotide frequencies showed substantially enhanced replication compared to wildtype. Host-driven effects on virus replication attenuation and enhancement were even more apparent in mouse and mosquito models. Infections with CpG-or UpA-high ZIKV mutants in mice did not cause typical ZIKV-induced tissue damage and completely protected mice during subsequent challenge with wildtype virus, which demonstrates their potential as live-attenuated vaccines. In contrast, the CpG-high mutants displayed enhanced replication in Aedes aegypti mosquitoes and a larger proportion of mosquitoes carried infectious virus in their saliva. These findings show that mosquito cells are also capable of discriminating RNA based on dinucleotide composition. However, the evolutionary pressure on the CpG dinucleotides of viral genomes in arthropod vectors directly opposes the pressure present in vertebrate host cells, which provides evidence that an adaptive compromise is required for arbovirus transmission. This suggests that the genome composition of arthropod-borne flaviviruses is crucial to maintain the balance between high-level replication in the vertebrate host and persistent replication in the mosquito vector.

microbiology↗