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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
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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”.