Comparative miRNA transcriptome analysis reveals miR-375-3p targets cyp19a and regulates ovarian development in Medaka (Oryzias latipes).

In teleosts, hormonal secretion from the pituitary gland exhibits significant sex plasticity, potentially linked to gonadal differentiation through the hypothalamic-pituitary-gonadal (HPG) axis. miRNAs, as transcriptional regulators, affecting gene expression by promoting mRNA degradation or suppressing translation. To explore the association between miRNAs and cyp19a and their potential role in reproduction, RNA sequencing (RNA-Seq) was conducted on male and female medaka brains. A total of 54 miRNAs were identified as significantly differentially expressed, with 45 showing female-biased expression and 9 exhibiting male-biased expression. qPCR analysis revealed that the expression levels of candidate miRNAs significantly differed between males and females as sex differentiation progressed. Additionally, cyp19a1a was highly expressed in the ovary, while cyp19a1b showed high expression in the brain. Treatment with the aromatase inhibitor exemestane (EM) induced male characteristics, leading to noticeable ovarian degeneration and cavitation. Following EM treatment, qPCR analysis showed an increase in miRNA expression, alongside a decrease in female development-related genes (foxl2, cyp19a1a, and cyp19a1b) and an increase in male development-related genes (dmy, cyp17a, and gsdf), compared to the control group. Additionally, a dual-luciferase reporter assay confirmed that miR-375-3p specifically binds to cyp19a1a and cyp19a1b. In conclusion, this study enhances the understanding of miRNA regulatory mechanisms in the brain, gonads, and reproductive development of medaka.