@article {7996, title = {Molecular and physiological characterization of a crustacean cardioactive signaling system in a lophotrochozoan - the Pacific oyster (Crassostrea gigas): a role in reproduction and salinity acclimation.}, journal = {J Exp Biol}, volume = {224}, year = {2021}, month = {2021 May 15}, abstract = {

The crustacean cardioactive peptide (CCAP) is an important neuropeptide involved in the regulation of a variety of physiological processes in arthropods. Although this family of peptides has an ancestral origin, its function remains poorly understood among protostome species - apart from arthropods. We functionally characterized three G protein-coupled receptors (GPCRs) in the oyster Crassostrea gigas, phylogenetically related to ecdysozoan CCAP receptors (CCAPRs) and to chordate neuropeptide S receptors (NPSRs). Cragi-CCAPR1 and Cragi-CCAPR2 were specifically activated by the Cragi-CCAP1 and Cragi-CCAP2 peptides, respectively, both derived from the same CCAP precursor. In contrast, Cragi-CCAPR3 was only partially activated by CCAP1 and CCAP2 at high concentrations. The Cragi-CCAPR1 and Cragi-CCAPR2 genes were expressed in various adult tissues. They are both most expressed in the gills, while Cragi-CCAPR3 is mainly expressed in the visceral ganglia (VG). Cragi-CCAP precursor transcripts are higher in the VG, the labial palps and the gills. Receptor and ligand-encoding transcripts are more abundantly expressed in the gonads in the first stages of gametogenesis, while the Cragi-CCAP precursor is upregulated in the VG in the last stages of gametogenesis. This suggests a role of the CCAP signaling system in the regulation of reproductive processes. A role in water and ionic regulation is also supported considering the differential expression of the CCAP signaling components in oysters exposed to brackish water.

}, issn = {1477-9145}, doi = {10.1242/jeb.241588}, author = {R{\'e}alis-Doyelle, Emilie and Julie Schwartz and Marie-Pierre Dubos and Pascal Favrel} } @article {7279, title = {A functional m6 A-RNA methylation pathway in the oyster Crassostrea gigas assumes epitranscriptomic regulation of lophotrochozoan development}, journal = {The FEBS Journal}, year = {2020}, month = {Jan-09-2020}, issn = {1742-464X}, doi = {10.1111/febs.15500}, url = {https://onlinelibrary.wiley.com/doi/abs/10.1111/febs.15500}, author = {Le Franc, Lorane and Bernay, Beno{\^\i}t and Petton, Bruno and Since, Marc and Pascal Favrel and Guillaume Rivi{\`e}re} } @article {6796, title = {Characterization of an evolutionarily conserved calcitonin signalling system in a lophotrochozoan, the Pacific oyster (Crassostrea gigas) }, journal = {The Journal of Experimental Biology}, volume = {222}, year = {2019}, month = {Jan-07-2019}, pages = {jeb201319}, issn = {0022-0949}, doi = {10.1242/jeb.201319}, url = {http://jeb.biologists.org/lookup/doi/10.1242/jeb.201319}, author = {Julie Schwartz and R{\'e}alis-Doyelle, Emilie and Marie-Pierre Dubos and Lefranc, Benjamin and Leprince, J{\'e}r{\^o}me and Pascal Favrel} } @article {6116, title = {Characterization of an evolutionarily conserved calcitonin signalling system in a lophotrochozoan, the Pacific oyster ().}, journal = {J Exp Biol}, volume = {222}, year = {2019}, month = {2019 Jul 05}, abstract = {

In Protostoma, the diuretic hormone 31 (DH31) signalling system was long considered as the orthologue of the chordate calcitonin (CT) signalling system. Using the Pacific oyster () transcriptomic database GigaTON, we characterized seven G-protein-coupled receptors (GPCRs) named Cragi-CTR1-7 and phylogenetically related to chordate CT receptors (CTRs) and to protostome DH31 receptors. Two CT precursors (Cragi-CTP1 and Cragi-CTP2) containing two CT-type peptides and encoded by two distinct genes with a similar organization were also characterized. These oyster neuropeptides (Cragi-CT1/2) exhibit the two N-terminal paired cysteine residues and, except CTP2-derived peptide (Cragi-CTP2dp), show the C-terminal proline-amide motif typical of deuterostome CT-type peptides. All mature Cragi-CTs except Cragi-CTP2dp were detected in visceral ganglion extracts using mass spectrometry. Cell-based assays revealed that the previously characterized oyster receptors Cg-CT-R and Cragi-CTR2 were specifically activated by Cragi-CT1b and Cragi-CT2, respectively. This activation does not require the co-expression of receptor activity-modifying proteins (RAMPs). Thus, oyster CT signalling appears functionally more closely related to vertebrate CT/CTR signalling than to calcitonin gene-related peptide/calcitonin receptor-like receptor (CGRP/CLR) signalling. Gene expression profiles in different adult tissues and in oysters acclimated to brackish water suggest the potential implication of both Cg-CT-R/Cragi-CT1b and Cragi-CTR2/Cragi-CT2 in water and ionic regulations, although with apparently opposite effects. The present study represents the first comprehensive characterization of a functional CT-type signalling system in a protostome and provides evidence for its evolutionarily ancient origin and its early role in osmotic homeostasis.

}, issn = {1477-9145}, doi = {10.1242/jeb.201319}, author = {Julie Schwartz and R{\'e}alis-Doyelle, Emilie and Marie-Pierre Dubos and Lefranc, Benjamin and Leprince, J{\'e}r{\^o}me and Pascal Favrel} } @article {6117, title = {Histone Methylation Participates in Gene Expression Control during the Early Development of the Pacific Oyster .}, journal = {Genes (Basel)}, volume = {10}, year = {2019}, month = {2019 09 10}, abstract = {

Histone methylation patterns are important epigenetic regulators of mammalian development, notably through stem cell identity maintenance by chromatin remodeling and transcriptional control of pluripotency genes. But, the implications of histone marks are poorly understood in distant groups outside vertebrates and ecdysozoan models. However, the development of the Pacific oyster is under the strong epigenetic influence of DNA methylation, and histone-demethylase orthologues are highly expressed during . early life. This suggests a physiological relevance of histone methylation regulation in oyster development, raising the question of functional conservation of this epigenetic pathway in lophotrochozoan. Quantification of histone methylation using fluorescent ELISAs during oyster early life indicated significant variations in monomethyl histone H3 lysine 4 (H3K4me), an overall decrease in H3K9 mono- and tri-methylations, and in H3K36 methylations, respectively, whereas no significant modification could be detected in H3K27 methylation. Early in vivo treatment with the JmjC-specific inhibitor Methylstat induced hypermethylation of all the examined histone H3 lysines and developmental alterations as revealed by scanning electronic microscopy. Using microarrays, we identified 376 genes that were differentially expressed under methylstat treatment, which expression patterns could discriminate between samples as indicated by principal component analysis. Furthermore, Gene Ontology revealed that these genes were related to processes potentially important for embryonic stages such as binding, cell differentiation and development. These results suggest an important physiological significance of histone methylation in the oyster embryonic and larval life, providing, to our knowledge, the first insights into epigenetic regulation by histone methylation in lophotrochozoan development.

}, issn = {2073-4425}, doi = {10.3390/genes10090695}, author = {Alexandre Fellous and Lefranc, Lorane and Jouaux, Aude and Goux, Didier and Pascal Favrel and Riviere, Guillaume} } @article {6849, title = {Histone Methylation Participates in Gene Expression Control during the Early Development of the Pacific Oyster Crassostrea gigas}, journal = {Genes}, volume = {10}, year = {2019}, month = {Jan-09-2019}, pages = {695}, doi = {10.3390/genes10090695}, url = {https://www.mdpi.com/2073-4425/10/9/695}, author = {Fellous, Alexandre and Le Franc, Lorane and Jouaux, Aude and Goux, Didier and Pascal Favrel and Guillaume Rivi{\`e}re} } @article {5782, title = {Molecular evolution and functional characterisation of insulin related peptides in molluscs: Contributions of Crassostrea gigas genomic and transcriptomic-wide screening}, journal = {Journal of Comparative Endocrinology}, volume = {271}, year = {2019}, pages = {15-29}, type = {research}, abstract = {

Insulin Related Peptides (IRPs) belong to the insulin superfamily and possess a typical structure with two chains,
B and A, linked by disulphide bonds. As the sequence conservation is usually low between members, IRPs are
classified according to the number and position of their disulphide bonds. In molluscan species, the first IRPs
identified, named Molluscan Insulin-related Peptides (MIPs), exhibit four disulphide bonds. The genomic and
transcriptomic data screening in the Pacific oyster Crassostrea gigas (Mollusc, Bivalvia) allowed us to identify six
IRP sequences belonging to three structural groups. Cg-MIP1 to 4 have the typical structure of MIPs with four
disulphide bonds. Cg-ILP has three disulphide bonds like vertebrate Insulin-Like Peptides (ILPs). The last one,
Cg-MILP7 has a significant homology with Drosophila ILP7 (DILP7) associated with two additional cysteines
allowing the formation of a fourth disulphide bond. The phylogenetic analysis points out that ILPs may be the
most ancestral form. Moreover, it appears that ILP7 orthologs are probably anterior to lophotrochozoa and
ecdysozoa segregation. In order to investigate the diversity of physiological functions of the oyster IRPs, we
combine in silico expression data, qPCR measurements and in situ hybridization. The Cg-ilp transcript, mainly
detected in the digestive gland and in the gonadal area, is potentially involved in the control of digestion and
gametogenesis. The expression of Cg-mip4 is mainly associated with the larval development. The Cg-mip
transcript shared by the Cg-MIP1, 2 and 3, is mainly expressed in visceral ganglia but its expression was also
observed in the gonads of mature males. This pattern suggested the key roles of IRPs in the control of sexual
reproduction in molluscan species.

}, author = {Ma{\"e}va Cherif{\textendash}Feildel and Clothilde Berthelin and B{\'e}atrice Adeline and Guillaume Rivi{\`e}re and Pascal Favrel and Kristell Kellner-Cousin} } @article {5564, title = {Characterization of a tachykinin signalling system in the bivalve mollusc Crassostrea gigas}, journal = {General and Comparative Endocrinology}, volume = {266}, year = {2018}, pages = {110-118}, type = {regular}, abstract = {

Although tachykinin-like neuropeptides have been identified in molluscs more than two decades ago, knowledge on their function and signalling has so far remained largely elusive. We developed a cell-based assay to address the functionality of the tachykinin G-protein coupled receptor (Cragi-TKR) in the oyster Crassostrea gigas. The oyster tachykinin neuropeptides that are derived from the tachykinin precursor gene Cragi-TK activate the Cragi-TKR in nanomolar concentrations. Receptor activation is sensitive to Ala-substitution of critical Cragi-TK amino acid residues. The Cragi-TKR gene is expressed in a variety of tissues, albeit at higher levels in the visceral ganglia (VG) of the nervous system. Fluctuations of Cragi-TKR expression is in line with a role for TK signalling in C. gigas reproduction. The expression level of the Cragi-TK gene in the VG depends on the nutritional status of the oyster, suggesting a role for TK signalling in the complex regulation of feeding in C. gigas.

}, doi = {https://doi.org/10.1016/j.ygcen.2018.05.003}, author = {Marie-Pierre Dubos and Sven Zels and Julie Schwartz and Jeremy Pasquier and Liliane Schoofs and Pascal Favrel} } @article {5707, title = {Emergence of a cholecystokinin/sulfakinin signalling system in Lophotrochozoa}, journal = {Scientific Reports}, volume = {8}, year = {2018}, month = {11/2018}, pages = {16424}, abstract = {Chordate gastrin/cholecystokinin (G/CCK) and ecdysozoan sulfakinin (SK) signalling systems represent divergent evolutionary scenarios of a common ancestral signalling system. The present article investigates for the first time the evolution of the CCK/SK signalling system in a member of the Lophotrochozoa, the second clade of protostome animals. We identified two G protein-coupled receptors (GPCR) in the oyster\ Crassostrea gigas\ (Mollusca), phylogenetically related to chordate CCK receptors (CCKR) and to ecdysozoan sulfakinin receptors (SKR). These receptors, Cragi-CCKR1 and Cragi-CCKR2, were characterised functionally using a cell-based assay. We identified di- and mono-sulphated forms of oyster Cragi-CCK1 (pEGAWDY(SO3H)DY(SO3H)GLGGGRF-NH2) as the potent endogenous agonists for these receptors. The Cragi-CCK genes were expressed in the visceral ganglia of the nervous system. The Cragi-CCKR1 gene was expressed in a variety of tissues, while Cragi-CCKR2 gene expression was more restricted to nervous tissues. An\ in vitro\ bioassay revealed that different forms of Cragi-CCK1 decreased the frequency of the spontaneous contractions of oyster hindgut. Expression analyses in oysters with contrasted nutritional statuses or in the course of their reproductive cycle highlighted the plausible role of Cragi-CCK signalling in the regulation of feeding and its possible involvement in the coordination of nutrition and energy storage in the gonad. This study confirms the early origin of the CCK/SK signalling system from the common bilaterian ancestor and delivers new insights into its structural and functional evolution in the lophotrochozoan lineage.}, doi = {doi.org/10.1038/s41598-018-34700-4}, url = {https://www.nature.com/articles/s41598-018-34700-4}, author = {Julie Schwartz and Marie-Pierre Dubos and Jeremy Pasquier and C{\'e}line Zatylny-Gaudin and Pascal Favrel} } @article {5031, title = {Dynamics of DNA methylomes underlie oyster development}, journal = {PLoS Genetics}, volume = {13}, year = {2017}, month = {06/2017}, pages = {e1006807}, type = {Research Paper}, url = {https:// doi.org/10.13 71/journal.p gen.1006807}, author = {Guillaume Rivi{\`e}re and Yan He and Samuele Tecchio and Elizabeth Crowell and Micha{\"e}l Gras and Pascal Sourdaine and Guo, Ximing and Pascal Favrel} } @article {4626, title = {Molecular characterization of an adipokinetic hormone-related neuropeptide (AKH) from a mollusk}, journal = {General and Comparative Endocrinology}, volume = {243}, year = {2017}, pages = {15-21}, author = {Marie-Pierre Dubos and Bernay, Beno{\^\i}t and Pascal Favrel} } @article {4419, title = {GigaTON: an extensive publicly searchable database providing a new reference transcriptome in the pacific oyster Crassostrea gigas.}, journal = {BMC Bioinformatics}, volume = {16}, year = {2015}, month = {2015}, pages = {401}, abstract = {

BACKGROUND: The Pacific oyster, Crassostrea gigas, is one of the most important aquaculture shellfish resources worldwide. Important efforts have been undertaken towards a better knowledge of its genome and transcriptome, which makes now C. gigas becoming a model organism among lophotrochozoans, the under-described sister clade of ecdysozoans within protostomes. These massive sequencing efforts offer the opportunity to assemble gene expression data and make such resource accessible and exploitable for the scientific community. Therefore, we undertook this assembly into an up-to-date publicly available transcriptome database: the GigaTON (Gigas TranscriptOme pipeliNe) database.

DESCRIPTION: We assembled 2204 million sequences obtained from 114 publicly available RNA-seq libraries that were realized using all embryo-larval development stages, adult organs, different environmental stressors including heavy metals, temperature, salinity and exposure to air, which were mostly performed as part of the Crassostrea gigas genome project. This data was analyzed in silico and resulted into 56621 newly assembled contigs that were deposited into a publicly available database, the GigaTON database. This database also provides powerful and user-friendly request tools to browse and retrieve information about annotation, expression level, UTRs, splice and polymorphism, and gene ontology associated to all the contigs into each, and between all libraries.

CONCLUSIONS: The GigaTON database provides a convenient, potent and versatile interface to browse, retrieve, confront and compare massive transcriptomic information in an extensive range of conditions, tissues and developmental stages in Crassostrea gigas. To our knowledge, the GigaTON database constitutes the most extensive transcriptomic database to date in marine invertebrates, thereby a new reference transcriptome in the oyster, a highly valuable resource to physiologists and evolutionary biologists.

}, keywords = {Animals, Base Sequence, Computational Biology, Crassostrea, Databases, Genetic, Gene Library, Gene Ontology, Genome, High-Throughput Nucleotide Sequencing, Molecular Sequence Data, Sequence Analysis, RNA, Software, Transcriptome}, issn = {1471-2105}, doi = {10.1186/s12859-015-0833-4}, author = {Guillaume Rivi{\`e}re and Klopp, Christophe and Ibouniyamine, Nabihoudine and Huvet, Arnaud and Boudry, Pierre and Pascal Favrel} } @article {3373, title = {Diversity of the RFamide peptide family in mollusks}, journal = {frontiers in endocrinology}, volume = {5}, year = {2014}, type = {review}, abstract = {

Since the initial characterization of the cardioexcitatory peptide FMRFamide in the bivalve
mollusk Macrocallista nimbosa, a great number of FMRFamide-like peptides (FLPs) have
been identified in mollusks. FLPs were initially isolated and molecularly characterized in
model mollusks using biochemical methods. The development of recombinant technologies
and, more recently, of genomics has boosted knowledge on their diversity in various
mollusk classes. Today, mollusk FLPs represent approximately 75 distinct RFamide peptides
that appear to result from the expression of only five genes: the FMRFamide-related
peptide gene, the LFRFamide gene, the luqin gene, the neuropeptide F gene, and the cholecystokinin/
sulfakinin gene. FLPs display a complex spatiotemporal pattern of expression
in the central and peripheral nervous system.Working as neurotransmitters, neuromodulators,
or neurohormones, FLPs are involved in the control of a great variety of biological
and physiological processes including cardiovascular regulation, osmoregulation, reproduction,
digestion, and feeding behavior. From an evolutionary viewpoint, the major challenge
will then logically concern the elucidation of the FLP repertoire of orphan mollusk classes
and the way they are functionally related. In this respect, deciphering FLP signaling pathways
by characterizing the specific receptors these peptides bind remains another exciting
objective.

}, author = {C{\'e}line Zatylny-Gaudin and Pascal Favrel} } @article {3395, title = {Functional characterization of a short neuropeptide F-related receptor in a lophotrochozoan, the mollusk Crassostrea gigas.}, journal = {J Exp Biol}, volume = {217}, year = {2014}, month = {2014 Aug 15}, pages = {2974-82}, abstract = {

Members of the short neuropeptide F (sNPF) family of peptides and their cognate receptors play key roles in a variety of physiological processes in arthropods. In silico screening of GigasDatabase, a specific expressed sequence tag database from the Pacific oyster Crassostrea gigas, resulted in the identification of a receptor (Cg-sNPFR-like) phylogenetically closely related to sNPF receptors (sNPFRs) of insects. A reverse endocrinology approach was undertaken to identify the peptide ligand(s) of this orphan receptor. Though structurally distinct from insect sNPFs, three RFamide peptides derived from the same precursor, i.e. GSLFRFamide, SSLFRFamide and GALFRFamide, specifically activate the receptor in a dose-dependent manner, with respective EC50 values (half-maximal effective concentrations) of 1.1, 2.1 and 4.1 μmol l(-1). We found that both Cg-sNPFR-like receptor and LFRFamide encoding transcripts are expressed in the oyster central nervous system and in other tissues as well, albeit at lower levels. Mass spectrometry analysis confirmed the wide distribution of LFRFamide mature peptides in several central and peripheral tissues. The Cg-sNPFR-like receptor was more abundantly expressed in ganglia of females than of males, and upregulated in starved oysters. In the gonad area, highest receptor gene expression occurred at the start of gametogenesis, when storage activity is maximal. Our results suggest that signaling of LFRFamide peptides through the Cg-sNPFR-like receptor might play a role in the coordination of nutrition, energy storage and metabolism in C. gigas, possibly by promoting storage at the expense of reproduction.

}, issn = {1477-9145}, doi = {10.1242/jeb.104067}, author = {Bigot, Laetitia and Beets, Isabel and Marie-Pierre Dubos and Boudry, Pierre and Schoofs, Liliane and Pascal Favrel} } @article {3394, title = {The Jumonji gene family in Crassostrea gigas suggests evolutionary conservation of Jmj-C histone demethylases orthologues in the oyster gametogenesis and development.}, journal = {Gene}, volume = {538}, year = {2014}, month = {2014 Mar 15}, pages = {164-75}, abstract = {

Jumonji (Jmj) proteins are histone demethylases, which control the identity of stem cells. Jmj genes were characterized from plants to mammals where they have been implicated in the epigenetic regulation of development. Despite the Pacific oyster Crassostrea gigas representing one of the most important aquaculture resources worldwide, the molecular mechanisms governing the embryogenesis and reproduction of this lophotrochozoan species remain poorly understood. However, annotations in the C. gigas EST library suggested the presence of putative Jumonji genes, raising the question of the conservation of this family of histone demethylases in the oyster. Using Primer walking, 5{\textquoteright}-RACE PCR and in silico analyses, we characterized nine Jumonji orthologues in the oyster, called Cg-Jmj, bearing conserved domains critical for putative histone demethylase activity. Phylogenic analyses revealed that oyster Jumonji cluster into two distinct groups: {\textquoteright}single-domain Jmj{\textquoteright} and {\textquoteright}multi-domain Jmj{\textquoteright}, and define 8 subgroups corresponding to each cognate orthologues in metazoans. RT-qPCR investigations showed specific regulations of Cg-Jmj mRNAs during the early development and along the reproduction cycle. Furthermore, in situ and in toto hybridizations indicate that oyster Jumonji genes are transcribed mostly within the gonad in adult oysters whereas they display a ubiquitous expression during embryonic and larval development. Our study demonstrates the presence of nine Jumonji orthologues in the oyster C. gigas. Their domain conservation and their expression profile suggest an implication during reproduction and development, questioning about the epigenetic regulation by histone methylation in lophotrochozoans.

}, keywords = {Animals, Base Sequence, Conserved Sequence, Crassostrea, Evolution, Molecular, Gametogenesis, Gene Expression Regulation, Developmental, Jumonji Domain-Containing Histone Demethylases, Molecular Sequence Data, Multigene Family, RNA, Messenger}, issn = {1879-0038}, doi = {10.1016/j.gene.2013.12.016}, author = {Alexandre Fellous and Pascal Favrel and Guo, Ximing and Guillaume Rivi{\`e}re} } @article {3397, title = {Neuropeptides encoded by the genomes of the Akoya pearl oyster Pinctata fucata and Pacific oyster Crassostrea gigas: a bioinformatic and peptidomic survey.}, journal = {BMC Genomics}, volume = {15}, year = {2014}, month = {2014}, pages = {840}, abstract = {

BACKGROUND: Oysters impart significant socio-ecological benefits from primary production of food supply, to estuarine ecosystems via reduction of water column nutrients, plankton and seston biomass. Little though is known at the molecular level of what genes are responsible for how oysters reproduce, filter nutrients, survive stressful physiological events and form reef communities. Neuropeptides represent a diverse class of chemical messengers, instrumental in orchestrating these complex physiological events in other species.

RESULTS: By a combination of in silico data mining and peptide analysis of ganglia, 74 putative neuropeptide genes were identified from genome and transcriptome databases of the Akoya pearl oyster, Pinctata fucata and the Pacific oyster, Crassostrea gigas, encoding precursors for over 300 predicted bioactive peptide products, including three newly identified neuropeptide precursors PFGx8amide, RxIamide and Wx3Yamide. Our findings also include a gene for the gonadotropin-releasing hormone (GnRH) and two egg-laying hormones (ELH) which were identified from both oysters. Multiple sequence alignments and phylogenetic analysis supports similar global organization of these mature peptides. Computer-based peptide modeling of the molecular tertiary structures of ELH highlights the structural homologies within ELH family, which may facilitate ELH activity leading to the release of gametes.

CONCLUSION: Our analysis demonstrates that oysters possess conserved molluscan neuropeptide domains and overall precursor organization whilst highlighting many previously unrecognized bivalve idiosyncrasies. This genomic analysis provides a solid foundation from which further studies aimed at the functional characterization of these molluscan neuropeptides can be conducted to further stimulate advances in understanding the ecology and cultivation of oysters.

}, issn = {1471-2164}, doi = {10.1186/1471-2164-15-840}, author = {Stewart, Michael J and Pascal Favrel and Rotgans, Bronwyn A and Wang, Tianfang and Zhao, Min and Sohail, Manzar and O{\textquoteright}Connor, Wayne A and Elizur, Abigail and Jo{\"e}l Henry and Cummins, Scott F} } @article {3396, title = {Temperature influences histone methylation and mRNA expression of the Jmj-C histone-demethylase orthologues during the early development of the oyster Crassostrea gigas.}, journal = {Mar Genomics}, year = {2014}, month = {2014 Sep 16}, abstract = {

In many groups, epigenetic mechanisms influence developmental gene regulation under environmental inputs. The Pacific oyster Crassostrea gigas belongs to lophotrochozoans and its larval development is highly dependent on temperature, but the role of epigenetic mechanisms in this context is unknown despite high levels of the recently characterized Jumonji histone demethylase (JHDM) orthologues (Cg_Jumonji) suggesting a physiological relevance of histone methylation in the oyster development. Because in other species alterations of the histone methylation pattern have deleterious outcomes, we investigated the influence of temperature during the oyster larval life on histone methylation and JHDM expression. To shed light on this point, oyster embryonic and early larval development experiments were carried out at different temperatures (18{\textdegree}C, 25{\textdegree}C and 32{\textdegree}C). Histone methylation levels were investigated using fluorescent ELISA at 6 and 24h post-fertilization. When compared to the 25{\textdegree}C group, at 18{\textdegree}C H3K4, H3K9 and H3K27 residues were hypomethylated at 6h post fertilization (hpf) and hypermethylated at 24hpf. In contrast, at 32{\textdegree}C, 6hpf animals present a dramatic hypermethylation (ca. 4-fold) of all examined residues, which is minored but sustained at 24hpf. RT-qPCR investigations of the mRNA expression of the nine oyster JHDMs, showed gene- and stage-specific temperature sensitivities throughout the early life of oysters. This study provides evidence of the biological significance of histone methylation during development in a lophotrochozoan species. Our results also indicate that temperature influences histone methylation, possibly through the expression level of putative actors of its regulation, which might participate in developmental control. To our knowledge, this is the first report indicating a direct relationship between an epigenetic mark and an environmental parameter in marine molluscs. Such investigations could help better understand the molecular mechanisms of development and adaptation in lophotrochozoans.

}, issn = {1876-7478}, doi = {10.1016/j.margen.2014.09.002}, author = {Alexandre Fellous and Pascal Favrel and Guillaume Rivi{\`e}re} } @article {3398, title = {Transcriptomic profiling of gametogenesis in triploid Pacific Oysters Crassostrea gigas: towards an understanding of partial sterility associated with triploidy.}, journal = {PLoS One}, volume = {9}, year = {2014}, month = {2014}, pages = {e112094}, abstract = {

BACKGROUND: Triploidy can occur in many animal species but is often lethal. Among invertebrates, amphibians and fishes, triploids are viable although often sterile or infertile. Most triploids of the Pacific oyster Crassostrea gigas are almost sterile (named "3nβ") yet a low but significant proportion show an advanced gametogenesis (named "3nα"). These oysters thus constitute an interesting model to study the effect of triploidy on germ cell development. We used microarrays to compare the gonad transcriptomes of diploid 2n and the abovementioned triploid 3nβ and 3nα male and female oysters throughout gametogenesis.

RESULTS: All triploids displayed an upregulation of genes related to DNA repair and apoptosis and a downregulation of genes associated with cell division. The comparison of 3nα and 3nβ transcriptomes with 2n revealed the likely involvement of a cell cycle checkpoint during mitosis in the successful but delayed development of gonads in 3nα individuals. In contrast, a disruption of sex differentiation mechanisms may explain the sterility of 3nβ individuals with 3nβ females expressing male-specific genes and 3nβ males expressing female-specific genes.

CONCLUSIONS: The disruption of sex differentiation and mitosis may be responsible for the impaired gametogenesis of triploid Pacific oysters. The function of the numerous candidate genes identified in our study should now be studied in detail in order to elucidate their role in sex determination, mitosis/meiosis control, pachytene cell cycle checkpoint, and the control of DNA repair/apoptosis.

}, issn = {1932-6203}, doi = {10.1371/journal.pone.0112094}, author = {Dheilly, Nolwenn M and Jouaux, Aude and Boudry, Pierre and Pascal Favrel and Christophe Lelong} }