Trascriptome-wide deregulation of gene expression in zebrafish exposed to artificial light at night

Urbanization and human activities are increasing global levels of artificial light at night (ALAN). Several studies have shown that ALAN negatively impacts wildlife, altering their perception, physiology, and behaviour, eventually leading to reduced fitness. ALAN also disrupts biological rhythms, affecting ability of animals to synchronize with natural cycles. There still is a critical lack of knowledge on the effects of ALAN on freshwater ecosystems, which are biodiversity hotspots and highly impacted. Our study aimed to understand the molecular effect of prolonged ALAN exposure in the zebrafish, already used as a research model in this field. Using high-throughput RNA sequencing, we investigated the transcriptome-wide gene expression responses in whole brains of ALAN exposed zebrafish. To identify daily changes in gene expression and metabolic pathways, samples were collected at four different timepoints along the day, two at daytime and two at nighttime. One month of exposure to ALAN induced deregulation of several genes and metabolic pathways both during the night, when zebrafish were directly exposed to artificial light, and during the day when they experienced natural light conditions. The highest number of differentially expressed genes were found at the early hours of the day and at night. Overall, the deregulated genes include both circadian clock genes and those related to immunity, stress response, responses to sensory stimuli, energy production, motor activity, and reproductive processes. These results provide new insights into the mechanisms through which ALAN affects animal biology, suggesting broader impacts than previously recognised. To safeguard aquatic ecosystems and their biodiversity, it is paramount to mitigate light pollution.