Biology subjects

Romatif, O.

Publications and source records attributed to Romatif, O..

8 recordsLinked to original sources

bioRxiv2026

Decoupling epigenetic variation from genetic variation reveals complementary dimensions of coral eco-evolutionary dynamics

Understanding how intraspecific diversity is structured is essential for predicting the eco-evolutionary trajectories of populations, especially under rapid environmental change. While such diversity has been extensively studied from a genetic perspective, much less is known about the distribution and ecological relevance of epigenetic variation within natural populations. To address this question, we focused on two species of reef-building corals belonging to distinct functional groups, Pocillopora acuta and Acropora hyacinthus, sampled across the South Pacific (New Caledonia, Fiji, French Polynesia). Using genome-wide Enzyme-Methyl sequencing, we jointly analyzed genetic (SNPs) and DNA methylation (CpGs) variation, while explicitly disentangling genetically associated from genetically independent epigenetic variation. Genetic and epigenetic structure showed contrasting spatial patterns, reflecting distinct temporal and ecological components of population dynamics. Genetic structure was strongest between archipelagos and followed an isolation-by-distance pattern consistent with long-term evolutionary processes. In contrast, epigenetic variation converged between colonies from different archipelagos. At finer spatial scales within archipelago, genetically independent epigenetic variation exhibited stronger structure than both genetic and genetically associated epigenetic variation, likely reflecting local environmental conditions. Together, our results show that genetic and epigenetic variation provide complementary insights into the eco-evolutionary processes shaping intraspecific diversity.

evolutionary biology↗

bioRxiv2025

Multi-Omics Reprogramming Drives a Counterintuitive Reversal of Disease Susceptibility During Ageing

Ageing is a progressive and irreversible biological process characterized by the deterioration of physiological functions and increased vulnerability to mortality. Although extensively studied in vertebrates, ageing in long-lived invertebrates remains comparatively unexplored. While ageing typically leads to greater susceptibility to infectious diseases, a striking and unexpected reversal was identified in oysters: older oysters exhibit markedly increased tolerance to the Pacific Oyster Mortality Syndrome (POMS), a panzootic disease primarily driven by the OsHV-1 herpesvirus and responsible for severe losses in global aquaculture. To investigate this counterintuitive pattern, we challenged oysters aged 4, 16, and 28 months from four biparental families and conducted an integrative multi-omics analysis, including epigenomics, transcriptomics, and metabolomics on the two families showing the strongest age-related increase in survival. Our results reveal that ageing in Magallana gigas is characterized by coordinated epigenetic, transcriptional, and metabolic reprogramming that reduces host permissiveness to POMS. We show that the epigenetic remodeling of key immune regulators (e.g., Toll-like receptors, MyD88) aligns with transcriptional rewiring of NF-{kappa}B and ubiquitin pathways, producing a finely tuned innate immune state marked by enhanced antiviral activity but reduced antibacterial responsiveness. We also identify age-related repression of mTOR signaling, likely promoting autophagy and improving viral control. These regulatory changes are tightly linked to metabolic adjustments, including reduced TCA cycle flux, remodeled nitrogen metabolism, and altered glutathione dynamics, which collectively support a stress-tolerant, energy-conserving phenotype. Together, our findings reveal a fundamental evolutionary trade-off: juveniles prioritize growth at the cost of viral susceptibility, whereas adults invest in cellular maintenance and antiviral preparedness.

genomics↗

bioRxiv2025

Bacteria with antibacterial activities isolated from Magallana gigas microbiota as potential probiotics against Vibrio aestuarianus infections in oyster farming

IntroductionOyster farming is a significant industry worldwide, but it is threatened by various diseases such as Pacific Oyster Mortality Syndrome or vibriosis. V. aestuarianus is a major cause of mortality for market-size oysters, resulting in significant economic losses for oyster farmers. Among the various control methods developed, probiotics appear to be a promising approach. More specifically, the use of the antibacterial activity of bacteria from the natural microbiota of the oyster Magallana gigas appears to be a sustainable solution against V. aestuarianus infections. ResultsOur study investigated the probiotic potential of bacteria isolated from the microbiota of M. gigas oysters. We screened a collection of 334 bacteria against eight target pathogens, including V. aestuarianus, and identified 78 bacteria with antibacterial activity for which eight retained this activity in their culture supernatants. Five strains were selected for further testing and exposed to oysters prior to V. aestuarianus infection. Our results show that four strains significantly reduced oyster mortality, with a maximum reduction of 70%. In addition, changes in oyster microbiota composition were observed following exposure, but the administered bacteria were not detected in the microbiota. ConclusionOur findings demonstrate the potential of oyster microbiota-derived bacteria as probiotics for disease control in oyster farming. This approach could provide a sustainable and environmentally friendly solution for the oyster farming industry. Further research is needed to understand the underlying mechanisms and to develop effective probiotic-based strategies for preventing V. aestuarianus infection.

microbiology↗

bioRxiv2025

An extracellular complex between CLE-1/collagen XV/XVIII and Punctin/MADD-4 defines cholinergic synapse identity

The precise localization of postsynaptic receptors opposite neurotransmitter release sites is essential for synaptic function. This alignment relies on adhesion molecules, intracellular scaffolds, and a growing class of extracellular scaffolding proteins. However, how these secreted proteins are retained at synapses remains unclear. We addressed this question using C. elegans neuromuscular junctions, where Punctin, a conserved extracellular synaptic organizer, positions postsynaptic receptors. We identified CLE-1, the ortholog of collagens XV/XVIII, as a key stabilizer of Punctin. Punctin and CLE-1B, the main isoform present at neuromuscular junctions, form a complex and rely on each other for synaptic localization. Punctin undergoes cleavage, and in the absence of CLE-1, specific fragments are lost, resulting in the mislocalization of cholinergic receptors to GABAergic synapses. Additionally, CLE-1 regulates receptor levels independently of Punctin. These findings highlight a crucial extracellular complex that maintains synapse identity.

neuroscience↗

bioRxiv2024

Diversity and functional specialization of oyster immune cells uncovered by integrative single cell level investigations

Mollusks are a major component of animal biodiversity and play a critical role in ecosystems and global food security. The Pacific oyster, Crassostrea (Magallana) gigas, is the most farmed bivalve mollusk in the world and is becoming a model species for invertebrate biology. Despite the extensive research on hemocytes, the immune cells of bivalves, their characterization remains elusive. Here we were able to extensively characterize the diverse hemocytes and identified at least seven functionally distinct cell types and three hematopoietic lineages. A combination of single-cell RNA sequencing, quantitative cytology, cell sorting, functional assays and pseudo-time analyses was used to deliver a comprehensive view of the distinct hemocyte types. This integrative analysis enabled us to reconcile molecular and cellular data and identify distinct cell types performing specialized immune functions, such as phagocytosis, reactive oxygen species production, copper accumulation, and expression of antimicrobial peptides. This study emphasized the need for more in depth studies of cellular immunity in mollusks and non-model invertebrates and set the ground for further comparative immunology studies at the cellular level.

immunology↗

bioRxiv2024

Microbial education plays a crucial role in harnessing the beneficial properties of microbiota for infectious disease protection in Crassostrea gigas

BackgroundRecently, the frequency and severity of marine diseases have increased in association with global changes, and molluscs of economic interest are particularly concerned. Among them, the Pacific oyster (Crassostrea gigas) production faces challenges from several diseases such as the Pacific Oyster Mortality Syndrome (POMS) or vibriosis. Various strategies such as genetic selection or immune priming have been developed to fight some of these infectious diseases. The microbial education, which consist of exposing the host immune system to beneficial microorganisms during early life stages is a promising approach against diseases. This study explores the concept of microbial education using controlled and pathogen-free bacterial communities and assesses its protective effects against POMS and Vibrio aestuarianus infections, highlighting potential applications in oyster production. ResultsWe demonstrate that it is possible to educate the oyster immune system by adding microorganisms during the larval stage. Adding culture based bacterial mixes to larvae protects only against the POMS disease while adding whole microbial communities from oyster donors protects against both POMS and vibriosis. The efficiency of the immune protection depends both on oyster origin and on the composition of the bacterial mixes used for exposure. No preferential protection was observed when the oysters were stimulated with their sympatric strains. We further show that the added bacteria were not maintained in the oyster microbiota after the exposure, but this bacterial addition induced long term changes in the microbiota composition and oyster immune gene expression. ConclusionOur study reveals successful immune system education of oysters by introducing beneficial micro-organisms during the larval stage. We improved the long-term resistance of oysters against critical diseases (POMS disease and Vibrio aestuarianus infections) highlighting the potential of microbial education in aquaculture.

microbiology↗

bioRxiv2023

Cooperation and cheating orchestrate Vibrio assemblages and polymicrobial synergy in oysters infected with OsHV-1 virus

Polymicrobial diseases significantly impact the health of humans and animals but remain understudied in natural systems. We recently described the Pacific Oyster Mortality Syndrome (POMS), a polymicrobial disease that impacts oyster production and is prevalent worldwide. Analysis of POMS-infected oysters on the French North Atlantic coast revealed that the disease involves co-infection with the endemic ostreid herpesvirus 1 (OsHV-1) and virulent bacterial species such as Vibrio crassostreae. However, it is unknown whether consistent Vibrio populations are associated with POMS in different regions, how Vibrio contribute to POMS, and how they interact with the OsHV-1 virus during pathogenesis. We resolved the Vibrio population structure in oysters from a Mediterranean ecosystem and investigated their functions in POMS development. We find that Vibrio harveyi and Vibrio rotiferianus are the predominant species found in OsHV-1-diseased oysters and show that OsHV-1 is necessary to reproduce the partition of the Vibrio community observed in the field. By characterizing the interspecific interactions between OsHV-1, V. harveyi and V. rotiferianus, we find that only V. harveyi synergizes with OsHV-1. When co-infected, OsHV-1 and V. harveyi behave cooperatively by promoting mutual growth and accelerating oyster death. V. harveyi showed high virulence potential in oysters and dampened host cellular defenses, making oysters a more favorable niche for microbe colonization. We next investigated the interactions underlying the co-occurrence of diverse Vibrio species in diseased oysters. We found that V. harveyi harbors genes responsible for the biosynthesis and uptake of a key siderophore called vibrioferrin. This important resource promotes the growth of V. rotiferianus, a cheater that efficiently colonizes oysters during POMS without costly investment in host manipulation nor metabolite sharing. By connecting field-based approaches, laboratory infection assays and functional genomics, we have uncovered a web of interdependencies that shape the structure and function of the POMS pathobiota. We showed that cooperative behaviors contribute to synergy between bacterial and viral co-infecting partners. Additional cheating behaviors further shape the polymicrobial consortium. Controlling such behaviors or countering their effects opens new avenues for mitigating polymicrobial diseases.

microbiology↗

bioRxiv2020

The HSPG Syndecan is a core organizer of cholinergic synapses in C. elegans

The extracellular matrix has emerged as an active component of chemical synapses regulating synaptic formation, maintenance and homeostasis. The heparan sulfate proteoglycan syndecans are known to regulate cellular and axonal migration in the brain. They are also enriched at synapses, but their synaptic functions remain more elusive. Here we show that SDN-1, the sole ortholog of syndecan in C. elegans, is absolutely required for the synaptic clustering of homomeric 7-like N-acetylcholine receptors (AChR) and regulates the synaptic content of heteromeric L-AChRs. SDN-1 is concentrated at neuromuscular junctions (NMJs) by the neurally-secreted synaptic organizer Ce-Punctin/MADD-4, which also activates the transmembrane netrin receptor DCC. Those cooperatively recruit the FARP and CASK orthologues that localize N-AChRs at cholinergic NMJs through physical interactions. Therefore, SDN-1 stands at the core of the cholinergic synapse organization by bridging the extracellular synaptic determinants to the intracellular synaptic scaffold that controls the postsynaptic receptor content.

neuroscience↗