Gene expression analysis in gonads of zebrafish (Danio rerio) subjected to masculinization treatments

Abstract

Fish exhibit all types of reproduction systems known in vertebrates in which sex determination and sex differentiation establish the final gender. Several environmental factors such as density, temperature or toxicity have been described to affect these two processes in fish, altering the final sex ratio. It is knownthat fish subjected to stress release higher cortisol plasma levels. Cortisol can, in turn, masculinize fish. In previous experiments using zebrafish (Danio rerio) in our laboratory, we have observed masculinization in fish subjected to either high density or cortisolt reated diets. Here, we aimed to understand the molecular mechanisms by which fish are masculinized by density and cortisol. For that purpose, we assessed gene expression in juvenile ovaries and testes by RTPCR of four canonical reproductionrelated genes, five genes involved in the glucocorticoid pathway and one epigenetic gene in fish subjected to different densities and cortisol treatments, during 6-90 and 10-45 days post fertilization, respectively. Results showed a significant downregulation of glucocorticoid receptor (nr3c1) in ovaries and testes and also downregulation of DNA methyltransferase 1 (dnmt1) and gonadal aromatase (cyp19a1a) in ovaries of fish subjected to high density. On the other hand, no differences in any of the studied genes were found in testes of fish fed with cortisol treated diets. In conclusion, this study shows that high density induced masculinization, involving changes in the expression of key sex differentiation genes, notably the downregulation of aromatase