Résumé
Sex in the Nile tilapia is controlled by sex chromosomes with an XX/XY system, by temperature and also by minor genetic factors. Nile tilapia aquaculture relies on male farming due to their better growth-rate and as a means to control reproduction. These males are usually produced by androgen treatments. Temperature-induced masculinisation is a feasible and a much more sustainable method to produce all-male offspring. High-temperatures applied during sex-differentiation induces masculinisation of XX females but the male proportion is dependent on the strain/population/family. The mechanisms generating these male phenotypes are poorly understood. At least one mode of action implies the DNA hypermethylation of the female aromatase cyp19a1a gene (responsible for estrogen biosynthesis), correlated with decreased cyp19a1a expression. Because fish methylated marks last after development, we analysed the DNA methylation in 3 months fish when gonads could be easily analysed. We performed a methylome study by MeDIP comparing ovaries and testis, of fish treated at 27°C or 36°C during sex-differentiation. MeDIP libraries were analysed between a high and a low thermosensitive family for which the sex-ratios at 36°C were of 90% and 59.8% males respectively. Differences of DNA methylated marks between control and treated males can be seen and are discussed with regard to gonadal gene expressions obtained by RNASeq.