Ecotoxicological and Molecular Profiling of Atrazine in <scp> <i>Hydra magnipapillata</i> </scp> Model: Disruption of Hippo Signalling and Induction of Oxidative Stress

Atrazine (ATZ), one of the most widely practiced herbicides, is recognized as an endocrine disruptor with insurmountable ecotoxicological consequences. While extensively studied in vertebrate models, its impact on early diverging metazoans remains poorly characterized. We investigated the effects of ATZ exposure on Hydra magnipapillata, considering its structural and functional alteration at organismal, cellular and molecular hierarchies. Feeding assays revealed dose- and duration-dependent morphological alterations, battery cell disruption and impairment of prey capture. Regeneration and budding were greatly inhibited, suggesting compromised stem cell activity. Acridine orange (AO) staining and comet assay confirmed apoptosis through DNA damage compounding with oxidative stress-mediated cytotoxicity. Transcription analysis revealed modulation of Hippo signalling (Hpo, LATS and Mob) and induction of oxidative stress markers (SOD, GST, CAT and Hsp70) together with upregulation of FoxO, reflecting conserved stress adaptive responses. Protein analysis revealed upregulation of StAR and downregulation of SRD5A2 and AKR1C2, demonstrating the disruption of steroidogenesis. These results indicate that ATZ interferes with conserved pathways associated with growth, stress resistance and steroid metabolism in Hydra, linking molecular alterations to impaired physiology. By integrating classical and molecular biomarkers, this study supports the use of Hydra as a sentinel model in ecotoxicology and provides comparative insights into evolutionary conservation of endocrine-disturbing effects of ATZ across metazoans.