Endocrine disrupting compounds in the environment, their impact on reproduction of Xenopus laevis, and basic mechanisms underlying sexual differentiation in amphibians

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Concerns have grown regarding the impact of endocrine disrupting compounds (EDCs) on the endocrine systems of various animals, leading to negative effects on reproductive biology, including reduced fertility and developmental abnormalities. This study explores several facets of this issue. Initially, the presence of EDCs with (anti)estrogenic and (anti)androgenic actions was assessed in water and sediment from the polluted Lambro River in Northern Italy, using yeast-based bioassays. Moderate estrogenic and significant anti-androgenic activities were detected at biologically relevant concentrations. Subsequently, the effects of EDCs on aquatic organisms were examined by exposing adult South African clawed toads (Xenopus laevis) to Lambro river water and specific EDC model compounds. Key endpoints included mRNA expression related to the hypothalamus-pituitary-gonad axis and liver biomarker genes, alongside plasma sex steroids and gonadal histology. Notable responses were primarily observed in (anti)estrogenic treatments, while gonadal histology proved to be the most sensitive indicator, revealing feminization in male toads exposed to river water. Lastly, the study analyzed the mechanisms of sexual differentiation in X. laevis, focusing on mRNA expressions of steroidogenic enzymes during tadpole development. Findings indicated that aromatase and 5α-reductase type 2 are crucial for gamete maturation, with disruptions in sperm matu