Steroid Signaling System Responds Differently to Temperature and Hormone Manipulation in the Red-Eared Slider Turtle (Trachemys scripta elegans), a Reptile with Temperature-Dependent Sex Determination

Abstract

Many reptiles, including the red-eared slider turtle (Trachemys scripta elegans), exhibit temperature-dependent sex determination (TSD). Temperature determines gonadal sex during the middle of embryogenesis, or the temperature-sensitive period (TSP), when gonadal sex is labile to both temperature and hormones – particularly estrogen. The biological actions of steroid hormones are mediated by their receptors as defined here as the classic transcriptional regulation of target genes. To elucidate estrogen action during sex determination, we examined estrogen receptor α (Esr1, hereafter referred to as ERα), estrogen receptor β (Esr2, hereafter referred to as ERβ), and androgen receptor (Ar, hereafter referred to as AR) expression in slider turtle gonads before, during and after the TSP, as well as following sex reversal via temperature or steroid hormone manipulation. ERα and AR levels spike at the female-producing temperature while ovarian sex is determined, but none of the receptors exhibited sexually dimorphic localization within the gonad prior to morphological differentiation. All three receptors respond differentially to sex-reversing treatments. When shifted to female-producing temperatures, embryos maintain ERα and AR expression while ERβ is reduced. When shifted to male-producing temperatures, medullary expression of all three receptors is reduced. Feminization via estradiol (E₂) treatment at a male-producing temperature profoundly changed the expression patterns for all three receptors. ERα and ERβ redirected to the cortex in E₂-created ovaries, while AR medullary expression was transiently reduced. Although warmer incubation temperature and estrogen result in the same endpoint (ovarian development), our results indicate different steroid signaling patterns between temperature- and estrogen-induced feminization.