@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 {3779, title = {Immune and Stress Responses in Oysters with Insights on Adaptation.}, journal = {Fish Shellfish Immunol}, year = {2015}, month = {2015 May 16}, abstract = {

Oysters are representative bivalve molluscs that are widely distributed in world oceans. As successful colonizers of estuaries and intertidal zones, oysters are remarkably resilient against harsh environmental conditions including wide fluctuations in temperature and salinity as well as prolonged air exposure. Oysters have no adaptive immunity but can thrive in microbe-rich estuaries as filter-feeders. These unique adaptations make oysters interesting models to study the evolution of host-defense systems. Recent advances in genomic studies including sequencing of the oyster genome have provided insights into oyster{\textquoteright}s immune and stress responses underlying their amazing resilience. Studies show that the oyster genomes are highly polymorphic and complex, which may be key to their resilience. The oyster genome has a large gene repertoire that is enriched for immune and stress response genes. Thousands of genes are involved in oyster{\textquoteright}s immune and stress responses, through complex interactions, with many gene families expanded showing high sequence, structural and functional diversity. The high diversity of immune receptors and effectors may provide oysters with enhanced specificity in immune recognition and response to cope with diverse pathogens in the absence of adaptive immunity. Some members of expanded immune gene families have diverged to function at different temperatures and salinities or assumed new roles in abiotic stress response. Most canonical innate immunity pathways are conserved in oysters and supported by a large number of diverse and often novel genes. The great diversity in immune and stress response genes exhibited by expanded gene families as well as high sequence and structural polymorphisms may be central to oyster{\textquoteright}s adaptation to highly stressful and widely changing environments.

}, issn = {1095-9947}, doi = {10.1016/j.fsi.2015.05.018}, author = {Guo, Ximing and He, Yan and Zhang, Linlin and Christophe Lelong and Jouaux, Aude} } @article {3828, title = {Transcriptome analysis reveals strong and complex antiviral response in a mollusc.}, journal = {Fish Shellfish Immunol}, year = {2015}, month = {2015 May 22}, abstract = {

Viruses are highly abundant in the oceans, and how filter-feeding molluscs without adaptive immunity defend themselves against viruses is not well understood. We studied the response of a mollusc Crassostrea gigas to Ostreid herpesvirus 1 {\textmu}Var (OsHV-1μVar) infections using transcriptome sequencing. OsHV-1μVar can replicate extremely rapidly after challenge of C.\ gigas as evidenced by explosive viral transcription and DNA synthesis, which peaked at 24 and 48\ h post-inoculation, respectively, accompanied by heavy oyster mortalities. At 120\ h post-injection, however, viral gene transcription and DNA load, and oyster mortality, were greatly reduced indicating an end of active infections and effective control of viral replication in surviving oysters. Transcriptome analysis of the host revealed strong and complex responses involving the activation of all major innate immune pathways that are equipped with expanded and often novel receptors and adaptors. Novel Toll-like receptor (TLR) and MyD88-like genes lacking essential domains were highly up-regulated in the oyster, possibly interfering with TLR signal transduction. RIG-1/MDA5 receptors for viral RNA, interferon-regulatory factors, tissue necrosis factors and interleukin-17 were highly activated and likely central to the oyster{\textquoteright}s antiviral response. Genes related to anti-apoptosis, oxidation, RNA and protein destruction were also highly up-regulated, while genes related to anti-oxidation were down-regulated. The oxidative burst induced by the up-regulation of oxidases and severe down-regulation of anti-oxidant genes may be important for the destruction of viral components, but may also exacerbate oyster mortality. This study provides unprecedented insights into antiviral response in a mollusc. The mobilization and complex regulation of expanded innate immune-gene families highlights the oyster genome{\textquoteright}s adaptation to a virus-rich marine environment.

}, issn = {1095-9947}, doi = {10.1016/j.fsi.2015.05.023}, author = {He, Yan and Jouaux, Aude and Ford, Susan E and Christophe Lelong and Pascal Sourdaine and Mathieu, Michel and Guo, Ximing} } @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} }