[Estrogen receptor Esr1 induces early ovarian differentiation in Trachemys scripta]

This study aims to explore the roles of three estrogen receptors (Esr1, Esr2, and Gper1) in early differentiation of embryonic gonads of Trachemys scripta. The expression characteristics of the receptor genes were studied first. The Esr1, Esr2, and Gper1 agonists PPT, WAY 200070, and G-1 were respectively injected into the embryos at the male-producing temperature (MPT) before initiation of gonadal differentiation. The sex reversal of the treated embryonic gonads was analyzed in terms of morphological structure of gonads, distribution pattern of germ cells, and expression of key genes and proteins involved in sex differentiation. The expression level of esr1 during the critical stage of sex differentiation was higher than those of esr2 and gper1 (very low expression) and was particularly high in the gonads at the female-producing temperature (FPT). After treatment with PPT, the MPT gonads presented obviously feminized morphology and structure, with the germ cells exhibiting a female distribution pattern. Furthermore, the mRNA expression levels of the key genes (dmrt1, amh, and sox9) for male differentiation were down-regulated significantly, while those of the key genes (foxl2 and cyp19a1) for female differentiation were up-regulated observably. The fluorescent signals of Amh and Sox9 expression almost disappeared, while Foxl2 and Arom were activated to express abundantly, which fully demonstrated the sex reversal of the gonads from male to female (sex reversal rate: 70.27%). However, the MPT gonads treated with WAY 200070 and G-1 still differentiated into testes, and the expression patterns of the key genes and proteins were similar to those in male gonads. The above results demonstrate that activation of Esr1 alone can fully initiate the early female differentiation process of gonads, suggesting that estrogen may induce early ovarian differentiation via Esr1 in Trachemys scripta. The findings provide a basis for further revealing the mechanisms of estrogen regulation in sex determination and differentiation of turtles.