Comprehensive analysis of genome‐wide DNA methylation and transcriptomics between ovary and testis in Monopterus albus

The ricefield eel (Monopterus albus), a protogynous hermaphroditic Synbranchiform species, is one of the most economically valuable freshwater fish in China. Studies on the sexual change of the ricefield eel will contribute to artificial culture and understanding the sex determination and differentiation in fish. In this study, the whole-genome DNA methylation and transcriptomes of ovary and testis were analysed in ricefield eel. An elevated methylation level in the genome was observed in the testis compared with the ovary. A total of 457 genes showed a negative correlation between DNA methylation status and expression level in the testis compared with the ovary. Of these genes, 16 candidates were screened on the basis of their vital roles reported in gonadal development. The methylation statuses and expression levels of dnmt3a, piwil1, tdrd1, sox30, nanos2, socs2, mei4 and zmiz1 were further validated using bisulphite sequencing PCR and quantitative real-time PCR respectively. These potential vital genes would be useful for future studies on the molecular mechanism of sex reversal in ricefield eel. Besides, the integrated analysis of DNA methylation and expression level of gonads provides basic information for epigenetic regulation in the process of sexual reversal in ricefield eel.