Unknown,Transcriptomics,Genomics,Proteomics

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Physiological change under OsHV-1 contamination in Pacific oyster Crassostrea gigas through massive mortality events on fields

ABSTRACT: Massive mortalities have been observed in France since 2008 on spat and juvenile Pacific oysters, Crassostrea gigas. A herpes virus called OsHV-1, easily detectable by PCR, has been implicated in the mortalities as demonstrated by the results of numerous field studies linking mortality with OsHV-1 prevalence. Moreover, experimental infections using viral particles have documented the pathogenicity of OsHV-1. The physiological responses of host to pathogen are not well known. In this study, a number of genes involved in the response to viral challenge have been identified and can be considered as confirmation of the role of the virus in the observed mortality. The aim of this study was to understand mechanisms brought into play against the virus during infection in the field. A microarray assay has been developed for a major part of the oyster genome and used for studying the host transcriptome. Spat with and without detectable OsHV-1 infection were compared by microarray during mortality episodes. The result allowed establishment of a hypothetic scheme of the host cell’s infection by, and response to, the pathogen. This response seems to be different to “sensu stricto” innate immunity through genic regulation of the virus life cycle. . Some regulatory response against the virus may explain that some oysters are able to survive infection by regulation of the viral genes associated with the OsHV-1 life cycle. Gene expression was measured from four individual animals of three sites, an oyster production area where mortalities on spat was observed in Spring (BL: Blainville sur mer) and two sanctuary sites (CRIC, Cricqueville en Bessin without production and CAB, an offshore storage structure)

ORGANISM(S): Crassostrea gigas

SUBMITTER: christophe lelong

PROVIDER: E-GEOD-46249 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Background The Pacific oyster Crassostrea gigas (Mollusca, Lophotrochozoa) is an alternative and irregular protandrous hermaphrodite. Little is known about the genetic and phenotypic bases of sex determinism in oysters, and little more about the molecular pathways regulating reproduction. We have recently developed and validated a microarray containing 31,918 oligomers (Dheilly et al., 2011) representing the oyster transcriptome. The application of this microarray to the study of mollusks gametogenesis should provide a better understanding of the key factors involved in sex differentiation and the regulation of oyster reproduction. Results Expression of the 31,918 ESTs was studied in gonads of oysters cultured along the French Atlantic coasts over a yearly reproductive cycle. Principal component analysis and hierarchical clustering first showed a significant divergence in gene expression patterns of males and females beginning when gonial mitosis started. Early expressed male-specific genes included bindin and female-specific genes included foxL2, a pancreatic lipase related protein, cd63 and vitellogenin. ANOVA analysis of the data further revealed 2482 genes differentially expressed during the course of males and/or females gametogenesis. The expression of 434 genes could be localized in either germ cells or somatic cells of the gonad by comparing the transcriptome of gonads to the transcriptomes of striped oocytes and somatic tissues. Analysis of the annotated genes revealed conserved molecular mechanisms between mollusks and mammals. Genes involved in chromatin condensation, DNA replication and repair, mitosis and meiosis regulation, transcription, translation and apoptosis were expressed in both male and female gonads. Additional lists of genes more specifically involved in either spermatogenesis (meiotic phase, in spermatozoids and mature sperm formation and in flagella structure and movement) or oogenesis (female sex differentiation, transcriptional regulation, cell cycle regulation and oocytes maturation) were also generated. Conclusions Our study provides novel insight into spermatogenesis and oogenesis in an alternative hermaphrodite bivalve, the Pacific oyster C. gigas. We identified genes opening new perspectives for functional studies of the signaling pathways implicated in gonad differentiation and development. Individual gonad oysters were sampled in 3 sites: site 1 = Locmariaquer (Brittany, France), site 2 = Baie des Veys (Normandy, France), and site 3 = Argenton (Brittany, France). 8 undifferentiated stage 0 gonads from site 1 were processed. 4 individuals from site 1 were processed for each gonad developmental stage and sex: stage 1 male, stage 1 female, stage 2 male, stage 2 female, stage 3 male, and stage 3 female. Pools of stage 3 females were prepared with individuals from site 1 and site 2 for biological validation of the results. Striped gonads from stage 3 females were prepared for prediction of gene expression localization.

Project description:Background Triploidy can occur in all species but is often lethal in birds and mammals. In amphibian, invertebrates and numerous species of fishes, triploid animals are viable and undistinguishable from diploid individuals. Gametogenesis is often affected and most animals are sterile for at least one sex, and gametes for the other sex are often unfertile. Although the majority of triploid oysters are sterile (beta individuals, 3nb), a low but persistent proportion of male and female animals produce gametes (alpha individuals, 3na). Thus, oysters constitute a unique model to study the effect of triploidy on germ cells development of both male and females. In this study, we used microarray to study the consequences of polyploidy on triploid oyster germ cells mitosis and meiosis. Results We compared the transcriptome of gonads of 3na and 3nb oyster gonads over the course of gametogenesis to the transcriptome of diploid (2n) oyster gonads. This study allowed us to reveal an increase in DNA repair and apoptosis through the NF-kappaB pathway, and a decrease in actin remodeling and chromatin remodeling in all 3n oysters. The comparison of 3na and 3nb individuals with 2n revealed that a pachytene checkpoints may be responsible for the success in gametogenesis of 3na individuals and for the observed delay in gametogenesis. However, the sterility of 3nb individuals can be explained by a disruption of sex determinism mechanisms. Indeed 3nb females express male-specific genes including enkurin and an Elav-like gene, and 3nb males express female-specific genes including Forkhead box L2 and beta-catenin. Conclusions Our results bring back to the front of the research field the questions of genetic sex determinism, mitosis/meiosis control, pachytene checkpoint, and cell type specific DNA damage pathways. Furthermore, this study identifies numerous new candidate genes which function should now be studied in details in oysters and in other triploid animals in order to elucidate the complex mechanisms involved in the regulation of triploid cells division. Triploid spats were obtained by crossing tetraploid males and diploid females in the ifremer experimental hatchery (La tremblade, Charente Maritime, France). We performed microarray analysis on a total of 35 individual triploid gonads that can be grouped as follow: 3n stage 0 (4 individuals), 3n alpha Stage 1 (8 individuals), 3n beta Stage 1 (8 individuals), 3n alpha Stage 3 male (4 individuals), 3n beta Stage 3 male (3 individuals), 3n alpha Stage 3 female (4 individuals), and 3n beta stage 3 female (4 individuals).

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Physiological change under OsHV-1 contamination in Pacific oyster Crassostrea gigas through massive mortality events on fields

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