Characterizing transcriptomic responses of southern flounder (Paralichthys lethostigma) chronically exposed to Deepwater Horizon oiled sediments

• Published in: Aquatic toxicology 2021-01, Vol.230, p.105716, Article 105716
• Main Authors: Rodgers, Maria L., Sherwood, Tracy A., Tarnecki, Andrea M., Griffitt, Robert J., Wetzel, Dana L.
• Format: Article
• Language: English
• Subjects: Animals; Cholesterol biosyntheis; Computational Biology; Deepwater Horizon; Flounder - genetics; Geologic Sediments - chemistry; Gills - chemistry; Gills - drug effects; Gulf of Mexico; Immune; Liver - chemistry; Liver - drug effects; Oil; Petroleum - toxicity; Petroleum Pollution - adverse effects; Southern flounder; Transcriptome - drug effects; Transcriptomics; Water Pollutants, Chemical - toxicity
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2020.105716

•Thyroid hormone metabolism-related pathways are impacted in gill tissue after oil exposure.•A recovery period increases the number of altered genes and pathways in gill and liver.•Cellular and humoral immune responses are significantly altered after a recovery period.•Cholesterol biosynthesis-related pathways are more suppressed after a recovery period. To obtain a deeper understanding of the transcriptomic responses to oil in southern flounder (Paralichthys lethostigma), we performed quantitative PCR and RNA sequencing on liver and gill tissue after a chronic exposure (35 days) to Deepwater Horizon crude oiled sediment and after a 30-day recovery period. We wanted to understand which specific genes are differentially expressed in liver and gill tissues directly after oiled sediment exposure and with the addition of a recovery period. Furthermore, we wanted to examine specific enriched pathways in these two tissues to determine the impact of exposure with and without a recovery period on biological processes (e.g. immune function). Liver and gill tissues were chosen because they represent two distinct organs that are highly important to consider when examining the impacts of oiled sediment exposure. The liver is the classic detoxification organ, while the gill is in direct contact with sediment in benthic fishes. Examination of these two tissues, therefore, generates a broad understanding of the transcriptomic consequences of oil exposure across an organism. Gene expression for interleukin 8 (il8) and interleukin 1B (il1β) was significantly increased versus control measurements for fish exposed to oiled sediments for 35 days in gill tissue. Hierarchical clustering of gene expression showed that tissue type was the main driver of gene expression (rather than treatment). The inclusion of a 30-day post-exposure recovery period showed a return of il8 and il1β gene expression in the gill to baseline expression levels. However, the recovery period increased the number of differentially expressed genes and significantly affected canonical pathways in both tissue types. Pathways related to cholesterol biosynthesis were significantly suppressed in oil-exposed flounder with a recovery period, but not in the exposed flounder without a recovery period. At the end of the exposure, 17 pathways were significantly affected in the gill, including thyroid hormone metabolism-related pathways, which were the most influenced. Liver tissue from the recovered fish had the great