Low-Dose Bisphenol A Induces Brain Aromatase (cyp19a1b) Expression in Male Zebrafish (Danio rerio): Implications for Endocrine-Active Substance Screening

Environmental endocrine-disrupting chemicals (EDCs) are linked to adverse reproductive and neuroendocrine outcomes in vertebrates. Bisphenol A (BPA), a high-production monomer used in plastics and resins, exhibits estrogenic activity and is detected in aquatic environments. In teleosts, the brain aromatase isoform cyp19a1b is an estrogen-responsive transcript enriched in radial glia and neurons, suggesting utility as a central nervous system biomarker of xenoestrogen exposure. Here, we partially cloned zebrafish cyp19a1b cDNA, examined its tissue distribution and neuroanatomical localization, and tested whether short-term exposure to 17β-estradiol (E2) or BPA modulates cyp19a1b expression in adult male brain. Semi-quantitative RT-PCR showed that cyp19a1b was abundant in female brain but scarce in peripheral tissues; in males, basal brain expression was low and testis was negative. In situ hybridization using a clone-derived, DIG-labeled probe revealed widespread labeling across the forebrain, optic tectum, cerebellar Purkinje cell layer, hypothalamic periventricular neurons and pituitary. Five-day BPA exposure elicited a non-monotonic (U-shaped) response, with significant induction at both low (10^？8 M) and high (10^？5 M) concentrations. These results indicate that adult male zebrafish brain retains inducible aromatase capacity and that cyp19a1b is sensitive to environmentally relevant low-dose BPA. Collectively, our findings support brain cyp19a1b as a practical neuroendocrine biomarker for endocrine-active substance screening and environmental monitoring and demonstrate that semi-quantitative RT-PCR can detect low-dose, non-monotonic dose-response behavior.