Biology subjects

Frangeul, L.

Publications and source records attributed to Frangeul, L..

13 recordsLinked to original sources

bioRxiv2025

The pupal stage is a developmental window for RNA virus persistence in Drosophila

RNA viruses establish persistent infections in insects through mechanisms that are not fully understood. We focused on three positive-sense RNA viruses that naturally establish persistent infections: Drosophila A virus (DAV), Drosophila C virus (DCV), and Nora virus. We examined how these viruses interact with their hosts during development and we found that pupal metamorphosis is a critical window where virus-host immune interactions influence persistence differently across viruses. Peak viral loads and replication occur during pupation, coinciding with increased endogenous reverse transcriptase activity. Notably, reverse transcription of viral RNA genomes produces viral DNA (vDNA) forms of DAV and DCV that are first detectable during pupation and are involved in persistence. In contrast, Nora virus achieves persistence without detectable vDNA. Immune responses during pupation are virus-specific, involving suppression of RNA interference components and varied regulation of JAK-STAT signaling. After metamorphosis, DAV continues producing vDNA into adulthood while DCV shows transient vDNA production, and Nora virus bypasses vDNA production altogether. These findings point to pupation as a key developmental stage for the establishment of persistent infections through distinct viral persistence strategies.

microbiology↗

bioRxiv2025

Spatio-temporal factors shape mosquito virome diversity and composition in a host and virus phylogeny-dependent manner

Beyond the arboviruses they transmit to humans and animals, mosquitoes harbour diverse viral communities that shape infection and immunity dynamics. Understanding how these communities shift within mosquito populations across time and space has important implications for how we anticipate and manage arboviral disease epidemics. Here, we examined the viromes of rural and sylvatic mosquito species sampled longitudinally across two years from countries representing South America, Africa, and Southeast Asian geographies to quantify the relative contributions of host and ecological factors in shaping their virome dynamics. We found that virus diversity and virome composition are strongly influenced by host phylogeny and spatial factors and show limited temporal variation. By examining virus similarity networks across mosquito species and biogeographies, we observed frequent instances of within- and cross-genus Culex-Anopheles virus sharing in Madagascar. Taken together, these findings inform the development and implementation strategies of any virome-based vector control technology and raise new evolutionary questions on how host generalism shapes the spatial prevalence of viruses and their potential for disease emergence.

microbiology↗

bioRxiv2024

Limited impact of the siRNA pathway on transposable element expression in Aedes aegypti

Transposable elements (TEs) are DNA sequences that can change their position within a genome. In the germline of arthropods, post-transcriptional regulation of TE expression is mainly mediated by the Piwi-interacting RNA (piRNA) pathway. piRNAs are small RNAs of 24-30 nucleotides (nt) in length produced from genomic precursor transcripts as well as through a ping-pong amplification cycle. In somatic tissues, certain insects, such as Drosophila, instead rely on the small interfering RNA (siRNA) pathway as a key regulator of TE expression. siRNAs are 21nt small RNAs produced from double-stranded RNA by the endonuclease Dicer2, which guides an RNA-induced silencing complex to degrade a complementary RNA. However, whether the siRNA pathway also regulates TE expression in the mosquito Aedes aegypti, a medically significant vector species with abundant somatic piRNAs, is unknown. To address this question, we investigated the expression of TEs and small RNAs in both somatic and gonadal tissues of a Dicer2 mutant line of Ae. aegypti and its wild-type counterpart. Our results show a modified pattern of TE expression and a decrease in TE-derived 21nt small RNAs in the Dicer2 mutant, but no major shift of TE transcript abundance. The lack of a functional siRNA pathway also causes perturbations in piRNA ping-pong signatures and the expression of certain piRNA-associated genes, but without clear evidence for compensation by increased piRNA pathway activity. We conclude that the mosquito Ae. aegypti produces siRNAs targeting TEs but these lack a critical role in the regulation of TE expression both in somatic and in gonadal tissues.

genomics↗

bioRxiv2024

Developmental emergence of first- and higher-order thalamic neuron molecular identities

The thalamus is organized into nuclei that have distinct input and output connectivities with the cortex. While first-order (FO) nuclei - also called core nuclei - relay input from sensory organs on the body surface and project to primary cortical sensory areas, higher-order (HO) nuclei - matrix nuclei - instead receive their driver input from the cortex and project to secondary and associative areas within cortico-thalamo-cortical loops. Input-dependent processes have been shown to play a critical role in the emergence of FO thalamic neuron identity from a ground state HO neuron identity, yet how this identity emerges during development remains unknown. Here, using single-cell RNA sequencing of the developing embryonic thalamus, we show that FO thalamic identity emerges after HO identity and that peripheral input is critical for the maturation of excitatory, but not inhibitory FO-type neurons. Our findings reveal that subsets of HO neurons are developmentally co-opted into FO-type neurons, providing a mechanistic framework for the diversification of thalamic neuron types during development and evolution. Summary StatementSubsets of higher-order thalamic neurons are developmentally co-opted into first-order type neurons, providing a framework for the diversification of thalamic neuron types during development and evolution.

neuroscience↗

bioRxiv2023

Viral infection disrupts intestinal homeostasis via Sting-dependent NF-kB signaling

Host-microbe interactions influence intestinal stem cell (ISC) activity to modulate epithelial turnover and composition. Here we investigated the functional impacts of viral infection on intestinal homeostasis and the mechanisms by which viral infection alters ISC activity. We report that Drosophila A virus (DAV) infection disrupts intestinal homeostasis in Drosophila by inducing sustained ISC proliferation, resulting in intestinal dysplasia, loss of gut barrier function, and reduced lifespan. We found that additional viruses common in laboratory-reared Drosophila also promote ISC proliferation. The mechanism of DAV-induced ISC proliferation involves progenitor-autonomous EGFR signaling, JNK activity in enterocytes, and requires Sting-dependent NF-kB (Relish) activity. We further demonstrate that activating Sting-Relish signaling is sufficient to induce ISC proliferation, promote intestinal dysplasia, and reduce lifespan in the absence of infection. Our results reveal that viral infection can significantly disrupt intestinal physiology, highlight a novel role for Sting-Relish signaling, and support a role for viral infection in aging. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/567400v1_ufig1.gif" ALT="Figure 1"> View larger version (40K): org.highwire.dtl.DTLVardef@1925c83org.highwire.dtl.DTLVardef@1f7b9fcorg.highwire.dtl.DTLVardef@d36c18org.highwire.dtl.DTLVardef@5dd16c_HPS_FORMAT_FIGEXP M_FIG C_FIG

microbiology↗

bioRxiv2023

Challenges in the Biotechnological Implementation of Oral RNA Interference as an Antiviral Strategy in Aedes aegypti

Mosquitoes, particularly Aedes aegypti, are critical vectors for globally significant pathogenic viruses. This study examines the limitations of oral RNA interference (RNAi) as a strategy to disrupt viral transmission by Ae. aegypti. We hypothesized that double-stranded RNA (dsRNA) targeting the Zika virus (ZIKV) or chikungunya virus (CHIKV) genomes produced by engineered bacterial symbionts could trigger an antiviral response. Mosquitoes mono-colonized with Escherichia coli producing dsZIK or dsCHIK did not display reduced viral titers following exposure to virus-contaminated bloodmeals and failed to generate dsZIK- or dsCHIK-derived small interfering RNAs. To address potential limitations of bacterial dsRNA release, we explored dsRNA inoculation via feeding and injection. While viral replication was impeded in mosquitoes injected with dsZIK or dsCHIK, no antiviral effect was observed in dsRNA-fed mosquitoes. These findings highlight complexities of implementing oral RNAi as an antiviral strategy in Ae. aegypti and warrant further exploration of local and systemic RNAi mechanisms.

microbiology↗

bioRxiv2023

Hsc70-4 mediates internalization of environmental dsRNA at the surface of Drosophila S2 cells

The siRNA pathway is the primary antiviral defense mechanism in invertebrates and plants. The systemic nature of this defense mechanism is one of its more fascinating characteristics and the recognition and transport of double-stranded RNA (dsRNA) of viral origin is required for the systemic activity of the siRNA pathway. Indeed, cellular internalization of dsRNA from the environment is a widespread phenomenon among insects. Here we aimed to identify cell surface proteins that bind to extracellular dsRNA and mediate its internalization. To this end, we developed a novel co-immunoprecipitation protocol that we followed with proteomics analysis. Among the hits from our screens was Hsc70-4, a constitutively expressed member of the heat shock protein family that has been implicated in clathrin-mediated endocytosis. We found that silencing Hsc70-4 impaired dsRNA internalization. Surprisingly, despite lacking a predicted transmembrane domain, Hsc70-4 localizes to the cell membrane and this localization was preserved when Hsc70-4 was expressed in mammalian cells, suggesting a conserved role at the cell surface. Furthermore, Hsc70-4 shows a previously undescribed dsRNA-specific binding capacity. Our results show that Hsc70-4 is a key element of the dsRNA internalization process and its detailed study may facilitate the development of RNA interference (RNAi)-based technologies for pest and vector borne disease control. ImportanceTo protect plants from pathogens or pests, the technology of "Host-induced gene silencing" has emerged as a powerful alternative to chemical treatments. This is an RNAi-based technology where small RNAs made in the plant silence the genes of the pests or pathogens that attack the plant. The small RNAs are generally derived from dsRNA expressed in transgenic plants. Alternatively, dsRNA can be sprayed onto the plant surface, where it can be taken up into the plant or ingested by pests. We have identified a cell surface protein that mediates the early steps of extracellular dsRNA internalization in insect cells. This could facilitate the development of new strategies for pest management.

cell biology↗

bioRxiv2022

Multifaceted contributions of Dicer2 to arbovirus transmission by Aedes aegypti

Arthropod-borne viruses (arboviruses) transmitted by Aedes aegypti mosquitoes are an increasing threat to global health. The small interfering RNA (siRNA) pathway is considered the main antiviral immune pathway of insects, and thus represents a potential key target in the development of novel transmission-blocking strategies against arboviruses. Although the antiviral function of the siRNA pathway in Ae. aegypti is well established, its effective impact on arbovirus transmission is surprisingly poorly understood. Here, we used CRISPR/Cas9-mediated gene editing to create a line of Ae. aegypti in which we mutated Dicer2, a gene encoding the RNA sensor and key component of the siRNA pathway. Our Dicer2 null mutant line is viable and fertile, and only displays minor fitness defects despite being unable to produce siRNAs. The loss of Dicer2 affects early viral replication and systemic viral dissemination of four medically significant arboviruses (chikungunya, Mayaro, dengue, and Zika viruses) representing two viral families. However, measures of virus transmission potential indicate that Dicer2 null mutants and wild-type mosquitoes display an overall similar level of vector competence. Additionally, Dicer2 null mutants undergo significant virus-induced mortality during infection with chikungunya virus, but not dengue virus. Together, our results define a multifaceted role for Dicer2 in the transmission of arboviruses by Ae. aegypti mosquitoes and pave the way for further mechanistic investigations.

microbiology↗

bioRxiv2022

Decoding rRNA Sequences for Improved Metagenomics in Sylvatic Mosquito Species

As mosquito-borne virus epidemics are often preceded by undetected spillover events, surveillance and virus discovery studies in non-urban mosquitoes informs pre-emptive and responsive public health measures. RNA-seq metagenomics is a popular methodology but it is constrained by overabundant rRNA. The lack of reference sequences for most mosquito species is a major impediment against physical and computational removal of rRNA reads. We describe a strategy to assemble novel rRNA sequences from mosquito specimens, producing an unprecedented dataset of 234 full-length 28S and 18S rRNA sequences of 33 medically important species from countries with known histories of mosquito-borne virus circulation (Cambodia, the Central African Republic, Madagascar, and French Guiana). We also evaluate the utility of rRNA sequences as molecular barcodes relative to the mitochondrial cytochrome c oxidase I (COI) gene. We show that rRNA sequences can be used for species identification when COI sequences are ambiguous or unavailable, revealing evolutionary relationships concordant with contemporary mosquito systematics. This expansion of the rRNA reference library improves mosquito RNA-seq metagenomics by permitting the optimization of species-specific rRNA depletion protocols for a broader species range and streamlined species identification by rRNA barcoding. In addition, rRNA barcodes could serve as an additional tool for mosquito taxonomy and phylogeny.

bioinformatics↗

bioRxiv2020

Non-retroviral endogenous viral element limits cognate virus replication in Aedes aegypti ovaries

Endogenous viral elements (EVEs) are viral sequences integrated in host genomes. A large number of non-retroviral EVEs was recently detected in Aedes mosquito genomes, leading to the hypothesis that mosquito EVEs may control exogenous infections by closely related viruses. Here, we experimentally investigated the role of an EVE naturally found in Aedes aegypti populations and derived from the widespread insect-specific virus, cell-fusing agent virus (CFAV). Using CRISPR/Cas9 genome editing, we created an Ae. aegypti line lacking the CFAV EVE. Absence of the EVE resulted in increased CFAV replication in ovaries, possibly modulating vertical transmission of the virus. Viral replication was controlled by targeting of viral RNA by EVE-derived piRNAs. Our results provide evidence that antiviral piRNAs are produced in the presence of a naturally occurring EVE and its cognate virus, demonstrating a functional link between non-retroviral EVEs and antiviral immunity in a natural insect-virus interaction.

microbiology↗

bioRxiv2020

Differential small RNA responses against co-infecting insect-specific viruses in Aedes albopictus mosquitoes

The mosquito antiviral response has been mainly studied in the case of arthropod-borne virus (arbovirus) infection in female mosquitoes. However, in nature, both female and male mosquitoes are abundantly infected with insect-specific viruses (ISVs). ISVs are capable of infecting the reproductive organs of both sexes and are maintained primarily by vertical transmission. Since the RNA interference (RNAi)-mediated antiviral response plays an important antiviral role in mosquitoes, ISVs constitute a relevant model to study sex-dependent antiviral responses. Using a naturally generated viral stock containing three distinct ISVs, Aedes flavivirus (AEFV), Menghai Rhabdovirus (MERV) and Shinobi tetra virus (SHTV), we infected adult Aedes albopictus females and males and generated small RNA libraries from ovaries, testes, and the remainder of the body. Overall, both female and male mosquitoes showed unique small RNA profiles to each co-infecting ISV regardless the sex or tissue tested. While all three ISVs generated virus-derived siRNAs, only MERV generated virus-derived piRNAs. We also studied the expression of PIWI genes in reproductive tissues and carcasses. Piwi1-4 were abundantly expressed in ovaries and testes in contrast to Piwi5-9, suggesting that Piwi 5-9 are involved in exogenous viral piRNA production. Together, our results show that ISV-infected Aedes albopictus produce viral small RNAs in a virus-specific manner and that male mosquitoes mount a similar small RNA-mediated antiviral response to that of females.

microbiology↗

bioRxiv2019

Tudor-SN promotes early replication of dengue virus in the Aedes aegypti midgut

Diseases caused by mosquito-borne viruses have been on the rise for the last decades, despite the implementation of vector control methods primarily based on insecticides. An alternative control method currently in development is the use of lab-engineered mosquitoes that are incapable to carry viruses. This has stimulated efforts to identify optimal target genes that are naturally involved in mosquito antiviral defenses or required for viral replication. Although several antiviral immune pathways such as RNA interference (RNAi) have been previously characterized in mosquitoes, the genes that prevent or promote early viral replication in the midgut remain elusive. Here, we investigated the role of a member of the Tudor protein family, Tudor-SN, upon dengue virus infection in the mosquito Aedes aegypti. Tudor-SN expression was upregulated early after dengue virus infection and was subsequently positively correlated with viral loads in the midgut. Using RNAi-mediated knockdown, we showed that the loss of Tudor-SN reduced dengue virus replication in the Ae. aegypti derived cell line Aag2 and in the midgut of Ae. aegypti females in vivo. Using immunofluorescence assays, we found that Tudor-SN localizes to the nucleolus in both Ae. aegypti and Aedes albopictus cells. Finally, we used a reporter assay to demonstrate that Tudor-SN was not required for RNAi function in vivo. Collectively, these results define a novel proviral role for Tudor-SN upon early dengue virus infection of the Ae. aegypti midgut.

microbiology↗

bioRxiv2017

Uncovering The Repertoire Of Endogenous Flaviviral Elements In Aedes Mosquito Genomes

Endogenous viral elements derived from non-retroviral RNA viruses were described in various animal genomes. Whether they have a biological function such as host immune protection against related viruses is a field of intense study. Here, we investigated the repertoire of endogenous flaviviral elements (EFVEs) in Aedes mosquitoes, the vectors of arboviruses such as dengue and chikungunya viruses. Previous studies identified three EFVEs from Ae. albopictus and one from Ae. aegypti cell lines. However, in-depth characterization of EFVEs in wild-type mosquito populations and individuals in vivo has not been performed. We detected the full-length DNA sequence of the previously described EFVEs and their respective transcripts in several Ae. albopictus and Ae. aegypti populations from geographically distinct areas. However, EFVE-derived proteins were not detected by mass spectrometry. Using deep sequencing, we detected the production of piRNA-like small RNAs in antisense orientation, targeting the EFVEs and their flanking regions in vivo. The EFVEs were integrated in repetitive regions of the mosquito genomes, and their flanking sequences varied among mosquito populations from different geographical regions. We bioinformatically predicted several new EFVEs from a Vietnamese Ae. albopictus population and observed variation in the occurrence of those elements among mosquito populations. Phylogenetic analysis of an Ae. aegypti EFVE suggested that it integrated prior to the global expansion of the species and subsequently diverged among and within populations. Together, this study revealed substantial structural and nucleotide diversity of flaviviral integrations in Aedes genomes. Unraveling this diversity will help to elucidate the potential biological function of these EFVEs.\n\nImportanceEndogenous viral elements (EVEs) are whole or partial viral sequences integrated in host genomes. Interestingly, some EVEs have important functions for host fitness and antiviral defense. Because mosquitoes also have EVEs in their genomes, we decided to thoroughly characterized them to lay the foundation of the potential use of these EVEs to manipulate the mosquito antiviral response. Here, we focused on EVEs related to the Flavivirus genus, to which dengue and Zika viruses belong, in Aedes mosquito individuals from geographically distinct areas. We showed the existence in vivo of flaviviral EVEs previously identified in mosquito cell lines and we detected new ones. We showed that EVEs have evolved differently in each mosquito population. They produced transcripts and small RNAs, but not proteins, suggesting a function at the RNA level. Our study uncovers the diverse repertoire of flaviviral EVEs in Aedes mosquito populations and suggests a role in the host antiviral system.

microbiology↗