Dimorphic DNA methylation during temperature-dependent sex determination in the sea turtle Lepidochelys olivacea

Sex determination in vertebrates depends on the expression of a conserved network of genes. Sea turtles such as Lepidochelys olivacea have temperature-dependent sex determination. The present work analyses some of the epigenetic processes involved in this. We describe sexual dimorphism in global DNA methylation patterns between ovaries and testes of L. olivacea and show that the differences may arise from a combination of DNA methylation and demethylation events that occur during sex determination. Irrespective of incubation temperature, 5-hydroxymethylcytosine was abundant in the bipotential gonad; however, following sex determination, this modification was no longer found in pre-Sertoli cells in the testes. These changes correlate with the establishment of the sexually dimorphic DNA methylation patterns, down regulation of Sox9 gene expression in ovaries and irreversible gonadal commitment towards a male or female differentiation pathway. Thus, DNA methylation changes may be necessary for the stabilization of the gene expression networks that drive the differentiation of the bipotential gonad to form either an ovary or a testis in L. olivacea and probably among other species that manifest temperature-dependent sex determination.