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GLOBAL TRANSCRIPT CHANGES IN THE LIVER OF POLAR COD (Boreogadus saida) EXPOSED TO DIFFERENT POLLUTANTS Knut Erik Tollefsen1,You Song1, Tore Høgåsen1, Siri Nesbakken2,3, Augustine Arukwe2, Lionel Camus4,5, Jasmine Nahrgang6,7, 1 Norwegian Institute for Water Research (NIVA), Gaustadalleen 21, N-0586 Oslo, Norway. Current address: National Registration Section, Norwegian Food Safety Authority, Pb.383, 2381 Brumunddal, Norway. 3Department of Biology, Norwegian University of Science & Technology (NTNU), Høgskoleringen 1, 7491 Trondheim, Trondheim, Norway. 4Akvaplanniva AS, 9296 Tromsø, Norway. 5Department of Engineering and Safety, UiT the Arctic University of Norway, 9037 Tromsø, Norway. 6Department of Arctic and Marine Biology, Faculty of Biosciences, Fisheries and Economics UiT the Arctic University of Norway, 9037 Tromsø, Norway. 7University Centre In Svalbard, 9171 Longyearbyen, Norway. 2 Corresponding Author: Knut Erik Tollefsen ([email protected]) ☐ Platform presentation ☐ Poster ☐ Either platform presentation or poster Preferred session theme: From mechanisms to ecological relevance (populations) Abstract Polar cod (Boreogadus saida) are susceptible to various pollutants and efforts to characterise the responses to environmental and anthropogenic stressors have been pointed out as key to performing risk assessment for this Arctic keystone species. As the exposure to single and mixtures of pollutants (and stressors) often lead to complex cellular responses, broad and unbiased approaches for assessing cellular perturbations (e.g. biomarkers) as predictors for higher organisational effects in polar cod are urgently needed. The main objectives of this work was to develop a global gene expression oligonucleotide micro array (oligoarray) and support bioinformatics solutions to identify the toxic Mode of Action (MoA) of both single and multiple stressors related to potential pollution scenarios in the Arctic. RNA deepsequencing of different tissue samples from fish exposed to various pollutants followed by denovo assembly of the Polar cod transcriptome were used to design a 83k high-density oligoarray. The array contained 82k transcripts with high quality annotations and about 50k transcripts with predicted protein coding regions. The performance of the arrays was verified by analyzing samples of polar cod exposed to the natural estrogen 17-estradiol (E2) by intraperitoneal injection, complex mixture of different PAHs and oil exposure (Water-borne and dietary exposure). The results obtained were compared to single gene expression analysis by qPCR and protein expression of well-known biomarkers for exposure to estrogens (vitellogenin) and PAH/oil exposure (CYP4501A). Results from the evaluation study show that the gene expression array identified a high number of genes being differentially expressed in the liver of polar cod after exposure to 5 mg/kg E2 and that this response were consistent with the regulation of estrogen-responsive genes. Dietary exposure to 0.16 and 20 ug/g (feed) of benzo(a)pyrene led to substantial hepatic transcriptional changes already at the lowest exposure concentration. Subsequent functional enrichment analysis revealed that these transcriptional changes were affecting a number of biological processes, including DNA damage and repair, apoptosis, transmembrane transport, immune responses, antioxidant activity, nuclear receptor activation and biotransformation. Pathway-analysis based on identification of gene (protein) orthologs in mammalian species supported the previous findings, and identified a number of toxic responses and pathways that were interrogated more in detail. The overall findings of the studies suggest that Polar cod respond in a similar manner as other fish species to exposure to estrogens, and that exposure to PAHs affect a number of toxicological responses related to detoxification and adverse effects such as DNA damage, cancer development, protein degradation, immune dysfunction. Acknowledgements: funding from ConocoPhilips, NFR-214184 POLARISATION, NFR-SIS (NIVA) project “MolPop”.