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.

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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Magallana gigas

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