Photoperiod-driven gene regulation in the brain of Chirostoma estor: endocrine, metabolic, and epigenetic insights

IntroductionAquatic light environments are increasingly altered by human activity, yet the endocrine and molecular mechanisms enabling fish to cope with extreme photoperiods remain poorly understood. This study investigates neuroendocrine and transcriptomic responses to continuous illumination in Chirostoma estor.MethodsWe conducted an in silico, hypothesis-driven reanalysis of a juvenile brain transcriptome obtained at 12 weeks post-hatching under continuous light (LL) or a control 12 h light: 12 h dark photoperiod. The analysis focused on genes associated with somatic growth, thyroid signaling, oxidative balance, appetite regulation, and epigenetic processes.ResultsContinuous illumination induced a transcriptional profile consistent with enhanced growth signaling sensitivity, including increased expression of growth hormone receptor and insulin-like growth factor pathway components, alongside reduced growth hormone transcripts and somatostatin receptor expression. Thyroid signaling showed reciprocal regulation of receptor isoforms, suggesting a growth-permissive mechanism. LL also upregulated antioxidant and redox-buffering genes, including mitochondrial uncoupling protein 2. In contrast, stress-axis regulators such as corticotropin-releasing factor and glucocorticoid receptor were more highly expressed under the control photoperiod. Epigenetic and nuclear architecture regulators displayed coordinated changes, indicating chromatin remodeling linked to selective pathway activation. Appetite-related genes showed mixed regulation patterns.DiscussionThese findings support a model in which continuous illumination promotes an alternative neuroendocrine state integrating growth-axis rewiring, oxidative stress protection, and epigenetic remodeling. This plastic response provides mechanistic insight into photoperiod-driven adaptation, with implications for understanding environmental light disruption and optimizing photoperiod management in aquaculture.