Epigenetics and oocyte quality of the Eurasian Perch

Gametes quality and proper embryogenesis of the offspring are tightly linked to each other. Gametogenesis mainly relies on regulations at hormonal, cellular, and molecular levels that can be affected by natural (e.g. feeding, stress) and non-natural (e.g. pollution, drugs) factors. During oogenesis, several types of molecules are deposited in developing oocytes and will be used by the developing embryos right after fertilization. Consequently, environmental factors are suggested to be a principal driver of oocyte quality. In mammals, the epigenetic landscape of developing oocytes and early embryos is currently intensively studied. Major global epigenetic changes are observed, which impact successful embryogenesis. In fish species, only a few studies have investigated DNA methylation changes in these developmental milestones. E.g. global DNA methylation reprogramming is absent in zebrafish, but shaping the epigenome in medaka; suggesting that this mechanism may depend upon the species that are subjected to specific environmental conditions and reproductive strategies. With more than 30.000 fish species known today, fish present a wide variety of reproduction strategies controlled by a variety of mechanisms, and only very little is known about the molecular regulations during oogenesis. In addition, fish species greatly depend upon their environment to trigger each step of their reproduction cycle. Consequently, understanding how environmental conditions may interfere with mechanisms controlling reproduction is highly important in fish species. In this context, the Eurasian perch belongs to an interesting candidate species, as their synchronous oogenesis is regulated in part by temperature variations. Moreover, the Eurasian perch is under increasing demand for the freshwater food industry, where he is subjected to increased domestication in aquaculture farms throughout European countries. Importantly, this growing demand for perch is facing a decline in reproductive success under captive conditions and would greatly benefit from understanding the impact of environmental factors on fish oocyte quality. We propose to decipher the occurrence and dynamics of epigenomic changes in perch oogenesis in relationship to environmental modifications. We hypothesize that observed heterogeneities in oocyte quality are correlated with an abnormal epigenomic landscape and transcriptome and that temperature fluctuations at the beginning of perch oogenesis interfere with epigenomic changes with severe consequences for oocyte quality. The anticipated results will help to understand the dynamic adaptation of fish to environmental modifications and the emergence of heterogenous oocyte quality. The analysis of the impact of environmental factors on the epigenome in perch oogenesis will lead to improved aquaculture methodologies and reproduction efficiencies in freshwater fish and provide a basis for understanding how climate changes affect reproduction in fish species.