Uncovering the transcriptional landscape of estrogen-induced gonadal feminization in the Chinese giant salamander.

Exogenous estrogen (17β-estradiol, E2) induces partial sex reversal in the Chinese giant salamander (CGS) at low concentrations (25 µg/L), and complete sex reversal at high concentrations (1000 µg/L), suggesting potential risks of skewed sex ratios in wild populations of this critically endangered species. Simultaneously, controlled sex reversal offers a strategy to enhance the aquaculture efficiency of captive CGS. However, the molecular mechanisms underlying this process remain largely unexplored. Here, we generated histological evidence of male-to-female sex reversal in CGS under E2 treatment and characterized dynamic, multi-timepoint transcriptomic changes during this process. Integrating histological and transcriptomic data, we identified 210 days post-hatching (120 days after hormone treatment) as a critical window for male gonadal sex reversal. During this period, E2 upregulates meiosis-related genes, promoting and maintaining the transition from male to female gonads. Concurrently, E2 suppresses DMRT1 expression, inhibiting male-specific differentiation pathways and facilitating testicular feminization. Notably, early E2 exposure increases CYP19A expression, but as E2 accumulates, it gradually supplants role of CYP19A in hormone-mediated regulation, resulting in a progressive decline of CYP19A function in gonads. These findings provide a comprehensive molecular and histological framework for understanding E2-induced sex reversal in CGS, offering crucial insights for the conservation of wild populations and for improving aquaculture practices.