Methylation pattern polymorphism of cyp19a in Nile tilapia and hybrids

Skewed sex development is prevalent in fish hybrids. However, the histological observation and molecular mechanisms remain elusive. In this study, we showed that the interspecific hybrids of the two fish species, and , had a male ratio of 98.02%. Microscopic examination revealed that the gonads of both male and female hybrids were developmentally retarded. Compared with the ovaries, the testes of both and hybrids showed higher DNA methylation level in two selected regions in the promoter of , the gonadal aromatase gene that converts androgens into estrogens, showed higher level gene expression in the ovary than in the testis in both and hybrid tilapia. Methylation and gene expression level of were negative correlation between the testis and ovary. Gene transcription was suppressed by the methylation of the promoter in vitro. While there is no obvious difference of the methylation level in testis or ovary between and hybrids. Thus, the DNA methylation of the promoter of may be an essential component of the sex maintenance, but not a determinant of high male ratio and developmental retardation of gonads in tilapia hybrids.