%0 Journal Article %J BMC Genomics %D 2015 %T Additive transcriptomic variation associated with reproductive traits suggest local adaptation in a recently settled population of the Pacific oyster, Crassostrea gigas. %A Sussarellu, Rossana %A Huvet, Arnaud %A Lapègue, Sylvie %A Virgile Quillien %A Christophe Lelong %A Cornette, Florence %A Jensen, Lasse Fast %A Bierne, Nicolas %A Boudry, Pierre %X

BACKGROUND: Originating from Northeast Asia, the Pacific oyster Crassostrea gigas has been introduced into a large number of countries for aquaculture purpose. Following introduction, the Pacific oyster has turned into an invasive species in an increasing number of coastal areas, notably recently in Northern Europe.

METHODS: To explore potential adaptation of reproductive traits in populations with different histories, we set up a common garden experiment based on the comparison of progenies from two populations of Pacific oyster sampled in France and Denmark and their hybrids. Sex ratio, condition index and microarray gene expression in gonads, were analyzed in each progeny (n = 60).

RESULTS: A female-biased sex-ratio and a higher condition index were observed in the Danish progeny, possibly reflecting an evolutionary reproductive strategy to increase the potential success of natural recruitment in recently settled population. Using multifarious statistical approaches and accounting for sex differences we identified several transcripts differentially expressed between the Danish and French progenies, for which additive genetic basis is suspected (showing intermediate expression levels in hybrids, and therefore additivity). Candidate transcripts included mRNA coding for sperm quality and insulin metabolism, known to be implicated in coordinated control and success of reproduction.

CONCLUSIONS: Observed differences suggest that adaptation of invasive populations might have occurred during expansion acting on reproductive traits, and in particular on a female-biased sex-ratio, gamete quality and fertility.

%B BMC Genomics %V 16 %P 808 %8 2015 %G eng %N 1 %R 10.1186/s12864-015-1972-8 %0 Journal Article %J Fish Shellfish Immunol %D 2015 %T Immune and Stress Responses in Oysters with Insights on Adaptation. %A Guo, Ximing %A He, Yan %A Zhang, Linlin %A Christophe Lelong %A Jouaux, Aude %X

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'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'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's adaptation to highly stressful and widely changing environments.

%B Fish Shellfish Immunol %8 2015 May 16 %G eng %R 10.1016/j.fsi.2015.05.018 %0 Journal Article %J Fish Shellfish Immunol %D 2015 %T Transcriptome analysis reveals strong and complex antiviral response in a mollusc. %A He, Yan %A Jouaux, Aude %A Ford, Susan E %A Christophe Lelong %A Pascal Sourdaine %A Mathieu, Michel %A Guo, Ximing %X

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 µVar (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'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's adaptation to a virus-rich marine environment.

%B Fish Shellfish Immunol %8 2015 May 22 %G eng %R 10.1016/j.fsi.2015.05.023 %0 Journal Article %J PLoS One %D 2014 %T Transcriptomic profiling of gametogenesis in triploid Pacific Oysters Crassostrea gigas: towards an understanding of partial sterility associated with triploidy. %A Dheilly, Nolwenn M %A Jouaux, Aude %A Boudry, Pierre %A Pascal Favrel %A Christophe Lelong %X

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.

%B PLoS One %V 9 %P e112094 %8 2014 %G eng %N 11 %R 10.1371/journal.pone.0112094