Epigenetic Control of Gonadal Aromatase (cyp19a1) in Temperature-Dependent Sex Determination of Red-Eared Slider Turtles

Abstract

In the red-eared slider turtle (Trachemys scripta), a species with temperature-dependent sex determination (TSD), the expression of the aromatase gene during gonad development is strictly limited to the female-producing temperature. The underlying mechanism remains unknown. In this study, we identified the upstream 5′-flanking region of the aromatase gene, gonad-specific promoter, and the temperature-dependent DNA methylation signatures during gonad development in the red-eared slider turtle. The 5′-flanking region of the slider aromatase exhibited sequence similarities to the aromatase genes of the American alligator, chicken, quail, and zebra finch. A putative TATA box was located 31 bp upstream of the gonad-specific transcription start site. DNA methylation at the CpG sites between the putative binding sites of the fork head domain factor (FOX) and vertebrate steroidogenic factor 1 (SF1) and adjacent TATA box in the promoter region were significantly lower in embryonic gonads at the female-producing temperature compared the male-producing temperature. A shift from male- to female-, but not from female- to male-, producing temperature changed the level of DNA methylation in gonads. Taken together these results indicate that the temperature, particularly female-producing temperature, allows demethylation at the specific CpG sites of the promoter region which leads the temperature-specific expression of aromatase during gonad development.

Incubation history prior to the canonical thermosensitive period determines sex in the American alligator

“…This initial portion of the TSP occurring before the onset of sexually dimorphic differentiation is more consistent with TSPs reported in turtle species, where thermosensitivity is observed prior to the sexually dimorphic gonadal differentiation and continues until shortly after this dimorphism is established (Bull & Vogt 1981, Pieau & Dorizzi 1981, Wibbels et al 1991. Recent reports in turtles and alligators have demonstrated a role for epigenetic patterning in coordinating sexually dimorphic gene expression (Matsumoto et al 2013. The finding that the effects on sex ratios resulting from pulses of FPT, occurring prior to the onset of histological and transcriptional sexual dimorphism, were not reversed by subsequent incubations provides insights into the stability of the mechanisms underlying this early thermosensitivity.…”

Dmrt1 induces the male pathway in a turtle with temperature-dependent sex determination

“…In this example, DNA methylation of the gonadal aromatase (Cyp19a1) promoter was associated with temperature-induced sex ratio shifts (NavarroMartín et al, 2011). In T. scripta, the DNA methylation level of the gonadal Cyp19a1 promoter was higher at MPT than FPT by stage 19 onwards, and was reduced in response to temperature shifts from MPT to FPT (Matsumoto et al, 2013a). Similarly, differential incubation temperatures resulted in dimorphic DNA methylation patterning of the Cyp19a1 and Sox9 promoters in gonads of American alligator embryos (Parrott et al, 2014).…”

“…Epigenetic mechanisms, including DNA methylation, histone modification and non-coding RNAs, can integrate environmental information with the regulation of gene expression, and have been emerging as a promising regulatory mechanism for TSD (Matsumoto et al, 2013a;Navarro-Martín et al, 2011;Parrott et al, 2014;Piferrer, 2013;Venegas et al, 2016). The first example of an epigenetic mechanism mediating temperature effects on sexual development in a vertebrate came from a study on the European sea bass, a fish with a polygenic system of sex determination where temperature and genetics contribute equally to sexual fate.…”

Gonadal Differentiation in Reptiles Exhibiting Environmental Sex Determination

“…In contrast to the CYP19A1 promoter, the SOX9 promoter is hypermethylated in the gonads of embryos incubated at FPT relative to MPT [Parrott et al, 2014]. Recent studies in the red-eared slider have also shown that the putative CYP19A1 promoter is methylated at elevated levels in those embryos incubated at MPT relative to those at FPT [Matsumoto et al, 2013]. This reported dimorphic methylation originates during the TSP, suggesting that it plays an integral role in sex determination.…”