Effects of Short-time Exposure to Atrazine on miRNA Expression Profiles in the Gonad of Common Carp (Cyprinus Carpio)

MicroRNAs (miRNAs) are endogenous small non-coding RNAs that negatively regulate gene expression by targeting specific mRNAs; they are involved in the modulation of important mRNA networks involved in toxicity. Atrazine is a known endocrine-disrupting chemical, whose molecular mechanisms are unknown. In this study, common carp (Cyprinus carpio) gonads at two key developmental stages were exposed to 0.428 ppb atrazine for 24 h in vitro. MiRNA expression profiles were analysed to identify miRNAs related to gonad development and to reveal the atrazine mechanisms interfering with gonad differentiation. Atrazine exposure caused significant alteration of multiple miRNAs. Compared with the juvenile ovary, more miRNAs were down-regulated in juvenile testis, some of these down-regulated miRNAs target the steroid hormone biosynthesis pathway related-genes. Predicted target genes of differently-expressed miRNAs after exposure to atrazine were involved in many reproductive biology signalling pathways. We suggest that these target genes may have important roles in atrazine-induced reproductive toxicity by altering miRNAs expression. Our results also indicate that atrazine can up-regulate aromatase expression through miRNAs, which supports the hypothesis that atrazine has endocrine-disrupting activity by altering the expression of genes of the Hypothalamus-Pituitary-Gonad axis through its corresponding miRNAs. This study tells us the following conclusions: 1. Atrazine exposure results in significant alterations of miRNAs whose predicted target genes are associated with reproductive processes. 2. In the primordial gonad, atrazine promoted the expression of early gonad-determining genes by decreasing specific miRNAs. 3. In the juvenile gonad, atrazine promoted the biosynthesis of steroid hormones.