Effects of Treatment with a DNA Methyltransferase Inhibitor 5-aza-dC on Sex Differentiation in Medaka (Oryzias latipes)

DNA methylation is a common epigenetic modification of DNA levels in the genome of eukaryotic cells, and an aberrant elevation of DNA methylation in gene promoter regions can inhibit gene expression. DNA methyltransferases (DNMTs) are involved in genomic DNA methylation, divided into maintenance DNA methyltransferases and de novo methylases, which are expressed to different degrees in the testis and ovaries. 5-aza-2'-deoxycytidine (5-aza-dC) is a cytidine analog with a strong methylation inhibition. In this experiment, medaka fish fries were treated with 5-aza-dC at 0 μg/L, 50 μg/L, and 100 μg/L. It was found that 100 g/L concentration of 5-aza-dC inhibited both body length and body weight of the adult fish, while 50 g/L concentration had no significant difference. In addition, paraffin section observation and gonad index statistics showed that after 100 g/L concentration of 5-aza-dC treatment, the gonad index of female fish increased significantly, but the gonad index of male fish had no significant difference. And the development of sperms and ovaries was normal without significant difference. Finally, we found that 5-aza-dC not only significantly decreased the transcription levels of <i>dnmt1</i> and <i>dnmt3bb.1</i>, but also significantly increased the expression levels of female-related genes such as <i>foxl2</i>, <i>cyp19a1</i> and <i>wnt4</i>, and significantly decreased the expression levels of male-related genes such as <i>dmrt1</i>, <i>sox9a</i> and <i>amh</i>. The DNA methylation patterns of <i>foxl2</i> and <i>dmrt1</i> genes were altered. This work provides more references for understanding the mechanism of DNA methylation affecting sex determination in fish.