Transgenerational epigenetic sex determination: Environment experienced by female fish affects offspring sex ratio.

Sex determination is a complex process that can be influenced by environment in various taxa. Disturbed environments can affect population sex ratios and thus threaten their viability. Emerging evidences support a role of epigenetic mechanisms, notably DNA methylation, in environmental sex determination (ESD). In this work, using zebrafish as model and a transgenerational experiment comprising 4 successive generations, we report a strength link between the promotor methylation level of three genes in female gonads and population sex ratio. One generation of zebrafish was exposed throughout its lifetime to cadmium (Cd), a non-essential metal, at an environmentally relevant concentration. The subsequent generations were not exposed. At the first and the third generation a subset of individuals was exposed to an elevated temperature, a well-known masculinizing factor in zebrafish. While heat was associated to an increase in the methylation level of cyp19a1a gene and population masculinization, foxl2a/dmrt1 methylation levels appeared to be influenced by Cd and fish density leading to offspring feminization. Ancestral Cd exposure indeed led to a progressive feminization of the population over generations and affected the sex plastic response of zebrafish in response to heat. The effect of Cd on the methylation level of foxl2a was observed until the third generation, supporting potential transgenerational inheritance. Our results support (i) a key role of cyp19a1a methylation in SD in zebrafish in response to environmental cues and (ii) the fact that the environment experienced by parents, namely mothers in the present case, can affect their offspring sex ratio via environment-induced DNA methylation changes in gonads.

Transfer and Transcriptomic Profiling in Liver and Brain of European Eels (Anguilla anguilla) After Diet-borne Exposure to Gold Nanoparticles.

A nanometric revolution is underway, promising technical innovations in a wide range of applications and leading to a potential boost in environmental discharges. The propensity of nanoparticles (NPs) to be transferred throughout trophic chains and to generate toxicity was mainly assessed in primary consumers, whereas a lack of knowledge for higher trophic levels persists. The present study focused on a predatory fish, the European eel (Anguilla anguilla) exposed to gold NPs (AuNPs; 10 nm, polyethylene glycol-coated) for 21 d at 3 concentration levels in food: 0 (NP0), 1 (NP1), and 10 (NP10) mg Au kg-1 . Transfer was assessed by Au quantification in eel tissues, and transcriptomic responses in the liver and brain were revealed by a high-throughput RNA-sequencing approach. Eels fed at NP10 presented an erratic feeding behavior, whereas Au quantification only indicated transfer to intestine and kidney of NP1-exposed eels. Sequencing of RNA was performed in NP0 and NP1 eels. A total of 258 genes and 156 genes were significantly differentially transcribed in response to AuNP trophic exposure in the liver and brain, respectively. Enrichment analysis highlighted modifications in the immune system-related processes in the liver. In addition, results pointed out a shared response of both organs regarding 13 genes, most of them being involved in immune functions. This finding may shed light on the mode of action and toxicity of AuNPs in fish. Environ Toxicol Chem 2020;39:2450-2461. © 2020 SETAC.