Biology subjects

Leroux, C.

Publications and source records attributed to Leroux, C..

7 recordsLinked to original sources

bioRxiv2026

Unraveling viral identity: Avoiding the trap of endogenous sequences for viral surveillance of small ruminant oncogenic retroviruses

Small ruminants (sheep and goats) are one of the few mammals in which an exogenous retrovirus (XRV) and closely related endogenous retroviral elements (ERV) coexist within the same host genome. The betaretroviruses Jaagsiekte sheep retrovirus (JSRV) and enzootic nasal tumor virus (ENTV) cause pulmonary and nasal adenocarcinomas, respectively, and share extensive sequence similarity with their endogenous counterparts. Consequently, molecular surveillance must rely on assays that can unequivocally distinguish true exogenous infection from ERV-derived templates; failure to do so compromises diagnosis, phylogenetic inference, and epidemiological conclusions. We retrieved all complete JSRV, ENTV-1/2, and related ERV genomes deposited in public repositories and performed a comprehensive alignment. Only a limited number of genomic segments were capable of distinguishing exogenous from endogenous sequences. We refer to these as discriminating regions (DRs). Phylogenies built using DRs revealed that several entries annotated as XRV are, in fact, ERV-derived or chimeric artefacts generated by short-amplicon reconstruction. A systematic literature review of over 100 articles identified 286 distinct primers and probes used for the XRV amplification. In-silico mapping of each oligonucleotide onto the full alignment showed that only 28 % reliably differentiate XRV from ERV. We experimentally validated the predictive power of this approach for 17 primer/probe sets, confirming that non-discriminating assays produce false-positive signals from endogenous templates. The misannotation of ERV sequences as exogenous viruses has resulting in the population of databases with dubious entries, fostering erroneous hypotheses such as vector-borne transmission of JSRV and ENTV. To address this issue, we propose a concise set of criteria for assay design, validation, and database annotation emphasizing DR targeting, specificity testing against endogenous templates, and transparent reporting. Although this framework was developed for small ruminants, it is readily applicable to any host-virus system in which exogenous viruses coexist with endogenous viral elements. This will strengthen viral surveillance, phylogenetics, and the One Health initiatives.

microbiology↗

bioRxiv2024

Association between genetic clades and cancer prevalence suggested by French-wide study of oncogenic small ruminant beta-retroviruses diversity

ENTV (Enzootic Nasal Tumor Virus) and JSRV (Jaagsiekte Sheep Retrovirus) are {beta}-retroviruses responsible for respiratory cancers in sheep and goats. In this study, we analyzed the genetic features of the sheep and goat {beta}-retrovirus (29 JSRV and 24 ENTV strains) circulating in France to identify molecular signatures associated with disease severity in flocks. We developed a highly specific PCR to amplify and sequence exogenous targeted regions or near full length proviruses based on limited discriminating motifs along their genomes. The phylogenetic reconstructions based on the LTR and env regions suggest that one major strain is circulating on the French territory for ENTV-1 and ENTV-2 while not clustering with already published Spanish, Canadian or Chinese strains. JSRV strains circulating in French sheep flocks were distributed in 2 distinct genetic clades clustering with sequences originating from North America, Africa and United-Kingdom. JSRV clade I was found to be associated with a higher incidence of cancer in French flocks. Specific motifs spanning the entire JSRV genome particularly in the LTRs and in the intracytoplasmic domain of the envelope were detected between the two genetic subtypes. This work represents the first nationwide study describing the circulation of the three closely related {beta}-oncogenic retrovirus JSRV, ENTV-1 and ENTV-2 in French sheep and goat flocks. Better characterization of strain genetics is a critical step in monitoring circulating {beta} retrovirus, especially those associated with higher cancer incidence in small ruminants.

pathology↗

bioRxiv2024

A genome-wide study of ruminants reveals two endogenous retrovirus families still active in goats

BackgroundEndogenous retroviruses (ERV) are traces of ancestral retroviral germline infections that constitute a significant portion of mammalian genomes and function as LTR-retrotransposons. ERVs remain understudied in ruminants and usually focus on specific families, highlighting a need for comprehensive and thorough exploration of the ERV landscape in these species. ResultsWe characterized 23 de novo Class I and II ERV families across four reference assemblies of domestic and wild sheep and goats, and one assembly of cattle. Among these families, 15 were shared by the five ruminant species, while six were exclusive to small ruminants and two were exclusive to cattle. The presence of these families in other ruminant species revealed multiple endogenization events over 40 million years. We identified a total of 113,812 ERV insertions across the five genomes, representing between 0.5 and 1% of their genomes. Solo-LTRs account for 84.5% of the annotated copies demonstrating that most of the ERVs are relics of past events. Although Class I ERVs showed similar sequence divergence landscapes between species, Class II ERVs displayed contrasting evolutionary dynamics. Families II-3 and II-5 showed higher abundance and copy conservation in small ruminants. Family II-5 was closely related to circulating exogenous retroviruses and was identified with 22 copies sharing identical LTRs and 12 with complete coding capacities in the domestic goat. ConclusionsOur results indicate that two ERV families may have retain their transpositional activity within ruminants, particularly in domestic goats, illustrating distinct evolutionary dynamics among ruminant species. This work highlights the ongoing influence of ERVs on genomic landscapes and provides further insights into their evolutionary trajectories in ruminant genomes.

evolutionary biology↗

bioRxiv2019

Metabolic complementarity between a brown alga and associated cultivable bacteria provide indications of beneficial interactions

Brown algae are key components of marine ecosystems and live in association with bacteria that are essential for their growth and development. Ectocarpus siliculosus is a genetic and genomic model for brown algae. Here we use this model to start disentangling the complex interactions that may occur between the algal host and its associated bacteria. We report the genome-sequencing of 10 alga-associated bacteria and the genome-based reconstruction of their metabolic networks. The predicted metabolic capacities were then used to identify metabolic complementarities between the algal host and the bacteria, highlighting a range of potentially beneficial metabolite exchanges between them. These putative exchanges allowed us to predict consortia consisting of a subset of these ten bacteria that would best complement the algal metabolism. Finally, co-culture experiments were set up with a subset of these consortia to monitor algal growth as well as the presence of key algal metabolites. Although we did not fully control but only modify bacterial communities in our experiments, our data demonstrated a significant increase in algal growth in cultures inoculated with the selected consortia. In several cases, we also detected, in algal extracts, the presence of key metabolites predicted to become producible via an exchange of metabolites between the alga and the microbiome. Thus, although further methodological developments will be necessary to better control and understand microbial interactions in Ectocarpus, our data suggest that metabolic complementarity is a good indicator of beneficial metabolite exchanges in holobiont.

systems biology↗

bioRxiv2018

Inferring biochemical reactions and metabolite structures to cope with metabolic pathway drift

Inferring genome-scale metabolic networks in emerging model organisms is challenging because of incomplete biochemical knowledge and incomplete conservation of biochemical pathways during evolution. This limits the possibility to automatically transfer knowledge from well-established model organisms. Therefore, specific bioinformatic tools are necessary to infer new biochemical reactions and new metabolic structures that can be checked experimentally. Using an integrative approach combining both genomic and metabolomic data in the red algal model Chondrus crispus, we show that, even metabolic pathways considered as conserved, like sterol or mycosporine-like amino acids (MAA) synthesis pathways, undergo substantial turnover. This phenomenon, which we formally define as \"metabolic pathway drift\", is consistent with findings from other areas of evolutionary biology, indicating that a given phenotype can be conserved even if the underlying molecular mechanisms are changing. We present a proof of concept with a new methodological approach to formalize the logical reasoning necessary to infer new reactions and new molecular structures, based on previous biochemical knowledge. We use this approach to infer previously unknown reactions in the sterol and MAA pathways.\n\nAuthor summaryGenome-scale metabolic models describe our current understanding of all metabolic pathways occuring in a given organism. For emerging model species, where few biochemical data are available about really occurring enzymatic activities, such metabolic models are mainly based on transferring knowledge from other more studied species, based on the assumption that the same genes have the same function in the compared species. However, integration of metabolomic data into genome-scale metabolic models leads to situations where gaps in pathways cannot be filled by known enzymatic reactions from existing databases. This is due to structural variation in metabolic pathways accross evolutionary time. In such cases, it is necessary to use complementary approaches to infer new reactions and new metabolic intermediates using logical reasoning, based on available partial biochemical knowledge. Here we present a proof of concept that this is feasible and leads to hypotheses that are precise enough to be a starting point for new experimental work.

systems biology↗

bioRxiv2018

Activation of the mTOR/ Akt pathway in thymic epithelial cells derived from thymomas

The pathogenesis of thymic epithelial tumors remains poorly elucidated. The PI3K/Akt/mTOR pathway plays a key role in various cancers; interestingly, several phase I/II study reported a positive effect of mTOR inhibitors in disease control in thymoma patients. A major limit for deciphering cellular and molecular events leading to the transformation of thymic epithelial cells or for testing drug candidates is the lack of reliable in vitro cell system\n\nWe analyzed protein expression and activation of key players of the Akt/mTOR pathway namely Akt, mTOR, and P70S6K in thirteen A, B and AB thymomas as well as in normal thymuses. While only Akt and the phospho-Akt were expressed in normal thymuses, both Akt and mTOR were activated, with B2 thymomas expressing higher level of activated phospho-Akt than A or AB subtypes. Phospho-P70S6K was expressed in all thymic tumors whatever their subtypes, and absent in normal thymus. Interestingly, in primary thymic epithelial cells maintained for short period of time after their derivation from seven AB and B thymomas, we report the activation of Akt; mTOR and P70S6. Finally, we analyzed the effect of mTOR inhibitor on thymoma derived epithelial cells and showed that rapamycin (100 nM/ ml) significantly reduced cell proliferation.\n\nOur results suggest that the activation of the Akt/ mTOR pathway might participate to the cell proliferation associated with tumor growth. Ultimately, our data enhance the potential role of thymic epithelial cells derived from tissue specimens for in vitro exploration of molecular abnormalities specific to rare thymic tumors.

cancer biology↗

bioRxiv2018

Visualizing structure-mediated interactions in supercoiled DNA molecules

We directly visualize the topology-mediated interactions between an unwinding site on a supercoiled DNA plasmid and a specific probe molecule designed to bind to this site, as a function of DNA supercoiling and temperature. The visualization relies on containing the DNA molecules within an enclosed array of glass nanopits using the Convex Lens-induced Confinement (CLiC) imaging method. This method traps molecules within the focal plane while excluding signal from out-of-focus probes. Simultaneously, the molecules can freely diffuse within the nanopits, allowing for accurate measurements of exchange rates, unlike other methods which could introduce an artifactual bias in measurements of binding kinetics. We demonstrate that the plasmids structure influences the binding of the fluorescent probes to the unwinding site through the presence, or lack, of other secondary structures. With this method, we observe an increase in the binding rate of the fluorescent probe to the unwinding site with increasing temperature and negative supercoiling. This increase in binding is consistent with the results of our numerical simulations of the probability of site-unwinding. The temperature dependence of the binding rate has allowed us to distinguish the effects of competing higher order DNA structures, such as Z-DNA, in modulating local site-unwinding, and therefore binding.

biophysics↗