Significant association of cyp19a promoter methylation with environmental factors and gonadal differentiation in olive flounder Paralichthys olivaceus.

The sex ratio of olive flounder Paralichthys olivaceus is sensitive to temperature or exogenous hormone exposures in the period of gonadal differentiation. Among sex-related genes, cyp19a, encoding cytochrome P450 aromatase, exhibits significant sex-dimorphic expression pattern and plays an important role in fish gonadal differentiation and development. The present study investigated the expression levels and promoter methylation dynamics of cyp19a and its regulators (nr5a2 and nr0b1), and sex-steroid hormone levels during flounder gonadal differentiation under the treatments of high temperature and estradiol-17β (E2). The results showed that levels of flounder cyp19a expression and estradiol-17β were repressed by high temperature treatment during this period. The up-regulation of nr5a2 by E2 treatment may be related to the all-female formation, and up-regulation of nr0b1 by high temperature treatment may be associated with masculinization. Co-transfection assay indicated that nr5a2 and nr0b1 were antagonist regulators of cyp19a. Furthermore, cyp19a promoter exhibited significant demethylation phenomenon at early stage of ovarian differentiation. While, high temperature could repress the demethylation process, resulting in hypermethylation maintenance in cyp19a promoter. The hypermethylation promoter was able to suppress cyp19a expression by blocking the nr5a2-mediated transactivation activity in vitro. The DNA methylation of epigenetic modification in cyp19a promoter might be the vital way linking environmental factors and gonadal differentiation in flounder.