Search

Biomphalaria glabratais a fresh-water mollusk that serves as obligatory intermediate host toSchistosoma mansoni, agent of the neglected tropical disease schistosomiasis that affects roughly 250 Mio people. One of the ways to control the pathogenic agent is to interrupt the life cycle by eliminating the intermediate snail host though foal treatment of water bodies with molluscicides. Currently recommended molluscicides were developed in the 1950ths and lack sufficient specificity, e.g., they are toxic to fish. To provide new lead compounds for the development of a new type of molluscicides we used a rational approach based on the hypotheses that interfering with an important epigenetic mark, DNA methylation, would impede development of the snail host. We present here the compound 29, analogues-based compound that mimic substrates of DNA methyltransferases. We show that compound 29 has (i) low cytotoxicity for human cells, (ii) it inhibits DNA methylation, and (iii) it decreases fecundity inB.glabrata. It is therefore conceivable to produce compounds that act as specific epigenetic molluscicides.

La production d’huîtres creuses est une des principales ressources aquacoles dans le monde. La France en est la principale productrice en Europe. Depuis ses débuts au tournant du XXe siècle, la production a toujours connu des épisodes de mortalité. Ainsi, les huîtres classiquement rencontrées sur nos côtes (Ostrea edulis) ont connu des mortalités massives dans les années 1920, puis ce fut le tour de l’huître portugaise à la fin des années 1960. L’introduction et la bonne adaptation des huîtres japonaises (Crassostrea gigas) dans les années 1970 se sont également accompagnées de divers épisodes depuis les années 1990, notamment liés au virus de l’herpès (OsHV-1) et aux bactéries Vibrio. Aujourd’hui, deux maladies touchent particulièrement les élevages ostréicoles. Le POMS d’une part, qui associe virus et bactéries, cause le syndrome de mortalité des juvéniles d’huître. Moins bien connue, la maladie des adultes est pour sa part due à Vibrio aesturianus. L’état des connaissances sur ces maladies a été présenté et discuté lors de la table-ronde du 16 mars 2022 (Mieux connaître l’état de santé des cheptels). La table-ronde du 11 mai 2022 s’est quant à elle focalisée sur les conséquences de ces mortalités dans le milieu ainsi que sur les travaux menés pour trouver des solutions pratiques permettant de les limiter. Ce qu’il faut retenir La présence d’huîtres moribondes et de chairs en décomposition dans la lagune lors des épisodes de mortalité n’est pas sans conséquences pour le milieu puisque des transferts de bactéries, virus, ammonium et phosphate ainsi que des changements de communautés planctoniques sont observés à proximité des lanternes d’huîtres. Côté solutions, plusieurs pistes prometteuses ont été présentées : la stimulation immunitaire, la sélection (épigénétique), la prise de probiotiques ainsi que certains changements de pratiques zootechniques, notamment l’exondation.

Snail-borne parasitic diseases represent an important challenge to human and animal health. Control strategies that target the intermediate snail host has proved very effective. Epigenetic mechanisms are involved in developmental processes and therefore play a fundamental role in developmental variation. DNA methylation is an important epigenetic information carrier in eukaryotes that plays a major role in the control of chromatin structure. Epigenome editing tools have been instrumental to demonstrate functional importance of this mark for gene expression in vertebrates. In invertebrates, such tools are missing, and the role of DNA methylation remains unknown. Here we demonstrate that methylome engineering can be used to modify in vivo the CpG methylation level of a target gene in the freshwater snail Biomphalaria glabrata, intermediate host of the human parasite Schistosoma mansoni. We used a dCas9-SunTag-DNMT3A complex and synthetic sgRNA to transfect B. glabrata embryos and observed an increase of CpG methylation at the target site in 50% of the hatching snails.

DNA-binding proteins play critical roles in many major processes such as development and sexual biology of Schistosoma mansoni and are important for the pathogenesis of schistosomiasis. Chromatin immunoprecipitation (ChIP) experiments followed by sequencing (ChIP-seq) are useful to characterize the association of genomic regions with posttranslational chemical modifications of histone proteins. Challenges in the standard ChIP protocol have motivated recent enhancements in this approach, such as reducing the number of cells required and increasing the resolution. In this chapter, we describe the latest advances made by our group in the ChIP methods to improve the standard ChIP protocol to reduce the number of input cells required and to increase the resolution and robustness of ChIP in S. mansoni.

Differentiated sex chromosomes are accompanied by a difference in gene dose between X/Z-specific and autosomal genes. At the transcriptomic level, these sex-linked genes can lead to expression imbalance, or gene dosage can be compensated by epigenetic mechanisms and results into expression level equalization. Schistosoma mansoni has been previously described as a ZW species (i.e., female heterogamety, in opposition to XY male heterogametic species) with a partial dosage compensation, but underlying mechanisms are still unexplored. Here, we combine transcriptomic (RNA-Seq) and epigenetic data (ChIP-Seq against H3K4me3, H3K27me3, and H4K20me1 histone marks) in free larval cercariae and intravertebrate parasitic stages. For the first time, we describe differences in dosage compensation status in ZW females, depending on the parasitic status: free cercariae display global dosage compensation, whereas intravertebrate stages show a partial dosage compensation. We also highlight regional differences of gene expression along the Z chromosome in cercariae, but not in the intravertebrate stages. Finally, we feature a consistent permissive chromatin landscape of the Z chromosome in both sexes and stages. We argue that dosage compensation in schistosomes is characterized by chromatin remodeling mechanisms in the Z-specific region.

Schistosomes are the causative agents of schistosomiasis, a neglected tropical disease affecting over 230 million peopleworldwide. Additionally to theirmajor impact onhuman health, they are alsomodels of choice in evolutionary biology. These parasitic flatworms are unique among the common hermaphroditic trematodes as they have separate sexes. This so-called "evolutionary scandal" displays a female heterogametic genetic sex-determination system(ZZ males and ZWfemales), aswell as a pronounced adult sexual dimorphism. These phenotypic differences are determined by a shared set of genes in both sexes, potentially leading to intralocus sexual conflicts. To resolve these conflicts in sexually selected traits, molecularmechanisms such as sex-biased gene expression could occur, but parent-of-origin gene expression also provides an alternative. In this work we investigated the lattermechanism, that is, genes expressed preferentially from either the maternal or the paternal allele, in Schistosoma mansoni species. To this end, transcriptomes from male and female hybrid adults obtained by strain crosses were sequenced. Strain-specific single nucleotide polymorphism (SNP) markers allowed us to discriminate the parental origin, while reciprocal crosses helped to differentiate parental expression from strain-specific expression. We identified genes containing SNPs expressed in a parent-of-origin manner consistent with paternal and maternal imprints. Although the majority of the SNPs was identified in mitochondrial and Z-specific loci, the remaining SNPs found inmale and female transcriptomeswere situated in genes that have the potential to explain sexual differences in schistosome parasites. Furthermore, we identified and validated four new Z-specific scaffolds.

XY systems usually show chromosome-wide compensation of X-linked genes, while in many ZW systems, compensation is restricted to a minority of dosage-sensitive genes. Why such differences arose is still unclear. Here, we combine comparative genomics, transcriptomics and proteomics to obtain a complete overview of the evolution of gene dosage on the Z-chromosome of Schistosoma parasites. We compare the Z-chromosome gene content of African (Schistosoma mansoni and S. haematobium) and Asian (S. japonicum) schistosomes and describe lineage-specific evolutionary strata. We use these to assess gene expression evolution following sex-linkage. The resulting patterns suggest a reduction in expression of Z-linked genes in females, combined with upregulation of the Z in both sexes, in line with the first step of Ohno's classic model of dosage compensation evolution. Quantitative proteomics suggest that post-transcriptional mechanisms do not play a major role in balancing the expression of Z-linked genes.

Biomphalaria snails are instrumental in transmission of the human blood fluke Schistosoma mansoni. With the World Health Organization's goal to eliminate schistosomiasis as a global health problem by 2025, there is now renewed emphasis on snail control. Here, we characterize the genome of Biomphalaria glabrata, a lophotrochozoan protostome, and provide timely and important information on snail biology. We describe aspects of phero-perception, stress responses, immune function and regulation of gene expression that support the persistence of B. glabrata in the field and may define this species as a suitable snail host for S. mansoni. We identify several potential targets for developing novel control measures aimed at reducing snail-mediated transmission of schistosomiasis.

Background The debilitating human disease schistosomiasis is caused by infection with schistosome parasites that maintain a complex lifecycle alternating between definitive (human) and intermediate (snail) hosts. While much is known about how the definitive host responds to schistosome infection, there is comparably less information available describing the snail's response to infection. Methodology/Principle findings Here, using information recently revealed by sequencing of the Biomphalaria glabrata intermediate host genome, we provide evidence that the predicted core snail DNA methylation machinery components are associated with both intra-species reproduction processes and inter-species interactions. Firstly, methyl-CpG binding domain protein (Bgmbd2/3) and DNA methyltransferase 1 (Bgdnmt1) genes are transcriptionally enriched in gonadal compared to somatic tissues with 5-azacytidine (5-AzaC) treatment significantly inhibiting oviposition. Secondly, elevated levels of 5-methyl cytosine (5mC), DNA methyltransferase activity and 5mC binding in pigmented hybrid-compared to inbred (NMRI)-B. glabrata populations indicate a role for the snail's DNA methylation machinery in maintaining hybrid vigour or heterosis. Thirdly, locus-specific detection of 5mC by bisulfite (BS)-PCR revealed 5mC within an exonic region of a housekeeping protein-coding gene (Bg14-3-3), supporting previous in silico predictions and whole genome BS-Seq analysis of this species' genome. Finally, we provide preliminary evidence for parasite-mediated host epigenetic reprogramming in the schistosome/snail system, as demonstrated by the increase in Bgdnmt1 and Bgmbd2/3 transcript abundance following Bge (B. glabrata embryonic cell line) exposure to parasite larval transformation products (LTP). Conclusions/Significance The presence of a functional DNA methylation machinery in B. glabrata as well as the modulation of these gene products in response to schistosome products, suggests a vital role for DNA

Environmental epigenetic is an emerging field that studies the cause-effect relationship between environmental factors and heritable trait via an alteration in epigenetic marks. This field has received much attentions since the impact of environmental factors on different epigenetic marks have been shown to be associated with a broad range of phenotypic disorders in natural ecosystems. Chemical pollutants have been shown to affect immediate epigenetic information carriers of several aquatic species but the heritability of the chromatin marks and the consequences for long term adaptation remain open questions. In this work, we investigated the impact of the diuron herbicide on the DNA methylation pattern of spat from exposed Crassotrea gigas genitors. This oyster is one of the most important mollusk species produced worldwide and a key coastal economic resource in France. The whole genome bisulfite sequencing (WGBS, BS-Seq) was applied to obtain a methylome at single nucleotide resolution on DNA extracted from spat issued from diuron exposed genitors comparatively to control spat. We showed that the parental diuron exposure has an impact on the DNA methylation pattern of its progeny. Most of the differentially methylated regions occurred within coding sequences and we showed that this change in methylation level correlates with RNA level only in a very small group of genes. Although the DNA methylation profile is variable between individuals, we showed conserved DNA methylation patterns in response to parental diuron exposure. This relevant result opens perspectives for the setting of new markers based on epimutations as early indicators of marine pollutions.

Background: Adaptive evolution is not possible without the generation of phenotypic variants. The origin of these variations has been a central topic in evolutionary biology. Up to now, it was commonly accepted that standing genetic variation is the only cause of phenotypic variants. However, epigenetic information is emerging as a complementary source of heritable phenotypic variation that contributes to evolution. The relative importance of genetics and epigenetics in generating heritable phenotypic variation is nevertheless a matter of debate. Results: We used a host-parasite system to address this question. The human blood fluke Schistosoma mansoni can adapt rapidly to new intermediate snail hosts. The interaction between parasite and mollusk is characterized by a compatibility polymorphism illustrating the evolutionary dynamics in this system. The principal molecular marker for compatibility (infection success) is the expression pattern of a group of polymorphic mucins (SmPoMuc) in the parasite. We show here that chromatin structure changes as the SmPoMuc promoters are the cause for SmPoMuc transcription polymorphism leading to phenotypic novelty and increase in infection success, i.e., fitness. Conclusion: We establish that epigenetic changes can be the major if not only cause of adaptive phenotypic variants in Schistosoma mansoni, suggesting that epimutations can provide material for adaptive evolution in the absence of genetic variation in other systems. In addition, our results indicate that epidrugs can be used to control parasite development but also parasite evolution.

Background Among more than 20,000 species of hermaphroditic trematodes, Schistosomatidae are unusual since they have evolved gonochorism. In schistosomes, sex is determined by a female heterogametic system, but phenotypic sexual dimorphism appears only after infection of the vertebrate definitive host. The completion of gonad maturation occurs even later, after pairing. To date, the molecular mechanisms that trigger the sexual differentiation in these species remain unknown, and in vivo studies on the developing schistosomulum stages are lacking. To study the molecular basis of sex determination and sexual differentiation in schistosomes, we investigated the whole transcriptome of the human parasite Schistosoma mansoni in a stage-and sex-comparative manner. Methodology/Principal Findings We performed a RNA-seq on males and females for five developmental stages: cercariae larvae, three in vivo schistosomulum stages and adults. We detected 7,168 genes differentially expressed between sexes in at least one of the developmental stages, and 4,065 of them were functionally annotated. Transcriptome data were completed with H3K27me3 histone modification analysis using ChIP-Seq before (in cercariae) and after (in adults) the phenotypic sexual dimorphism appearance. In this paper we present (i) candidate determinants of the sexual differentiation, (ii) sex-biased players of the interaction with the vertebrate host, and (iii) different dynamic of the H3K27me3 histone mark between sexes as an illustration of sex-biased epigenetic landscapes. Conclusions/Significance Our work presents evidence that sexual differentiation in S. mansoni is accompanied by distinct male and female transcriptional landscapes of known players of the host-parasite crosstalk, genetic determinants and epigenetic regulators. Our results suggest that such combination could lead to the optimized sexual dimorphism of this parasitic species. As S. mansoni is pathogenic for humans, this study represents a prom

Background Chromatin structure can control gene expression and can define specific transcription states. For example, bivalent methylation of histone H3K4 and H3K27 is linked to poised transcription in vertebrate embryonic stem cells (ESC). It allows them to rapidly engage specific developmental pathways. We reasoned that non-vertebrate metazoans that encounter a similar developmental constraint (i.e. to quickly start development into a new phenotype) might use a similar system. Schistosomes are parasitic platyhelminthes that are characterized by passage through two hosts: a mollusk as intermediate host and humans or rodents as definitive host. During its development, the parasite undergoes drastic changes, most notable immediately after infection of the definitive host, i.e. during the transition from the free-swimming cercariae into adult worms. Methodology/Principal Findings We used Chromatin Immunoprecipitation followed by massive parallel sequencing (ChIP-Seq) to analyze genome-wide chromatin structure of S. mansoni on the level of histone modifications (H3K4me3, H3K27me3, H3K9me3, and H3K9ac) in cercariae, schistosomula and adults (available at http://genome.univ-perp.fr). We saw striking differences in chromatin structure between the developmental stages, but most importantly we found that cercariae possess a specific combination of marks at the transcription start sites (TSS) that has similarities to a structure found in ESC. We demonstrate that in cercariae no transcription occurs, and we provide evidences that cercariae do not possess large numbers of canonical stem cells. Conclusions/Significance We describe here a broad view on the epigenome of a metazoan parasite. Most notably, we find bivalent histone H3 methylation in cercariae. Methylation of H3K27 is removed during transformation into schistosomula (and stays absent in adults) and transcription is activated. In addition, shifts of H3K9 methylation and acetylation occur towards upstream and downstrea

Global change and its associated temperature increase has directly or indirectly changed the distributions of hosts and pathogens, and has affected host immunity, pathogen virulence and growth rates. This has resulted in increased disease in natural plant and animal populations worldwide, including scleractinian corals. While the effects of temperature increase on immunity and pathogen virulence have been clearly identified, their interaction, synergy and relative weight during pathogenesis remain poorly documented. We investigated these phenomena in the interaction between the coral Pocillopora damicornis and the bacterium Vibrio coralliilyticus, for which the infection process is temperature-dependent. We developed an experimental model that enabled unraveling the effects of thermal stress, and virulence vs. non-virulence of the bacterium. The physiological impacts of various treatments were quantified at the transcriptome level using a combination of RNA sequencing and targeted approaches. The results showed that thermal stress triggered a general weakening of the coral, making it more prone to infection, non-virulent bacterium induced an 'efficient' immune response, whereas virulent bacterium caused immuno-suppression in its host.

The digenetic trematode Schistosoma mansoni is a human parasite that uses the mollusc Biomphalaria glabrata as intermediate host. Specific S. mansoni strains can infect efficiently only certain B. glabrata strains (compatible strain) while others are incompatible. Strain-specific differences in transcription of a conserved family of polymorphic mucins (SmPoMucs) in S. mansoni are the principle determinants for this compatibility. In the present study, we investigated the bases of the control of SmPoMuc expression that evolved to evade B. glabrata diversified antigen recognition molecules. We compared the DNA sequences and chromatin structure of SmPoMuc promoters of two S. mansoni strains that are either compatible (C) or incompatible (IC) with a reference snail host. We reveal that although sequence differences are observed between active promoter regions of SmPoMuc genes, the sequences of the promoters are not diverse and are conserved between IC and C strains, suggesting that genetics alone cannot explain the evolution of compatibility polymorphism. In contrast, promoters carry epigenetic marks that are significantly different between the C and IC strains. Moreover, we show that modifications of the structure of the chromatin of the parasite modify transcription of SmPoMuc in the IC strain compared to the C strain and correlate with the presence of additional combinations of SmPoMuc transcripts only observed in the IC phenotype. Our results indicate that transcription polymorphism of a gene family that is responsible for an important adaptive trait of the parasite is epigenetically encoded. These strain-specific epigenetic marks are heritable, but can change while the underlying genetic information remains stable. This suggests that epigenetic changes may be important for the early steps in the adaptation of pathogens to new hosts, and might be an initial step in adaptive evolution in general.