Differential Gene Expression Induced by Exposure of Captive Mink to Fuel Oil: A Model for the Sea Otter

Abstract

Free-ranging sea otters are subject to hydrocarbon exposure from a variety of sources, both natural and anthropogenic. Effects of direct exposure to unrefined crude oil, such as that associated with the Exxon Valdez oil spill, are readily apparent. However, the impact of subtle but pathophysiologically relevant concentrations of crude oil on sea otters is difficult to assess. The present study was directed at developing a model for assessing the impact of low concentrations of fuel oil on sea otters. Quantitative PCR was used to identify differential gene expression in American mink that were exposed to low concentrations of bunker C fuel oil. A total of 23 genes, representing 10 different physiological systems, were analyzed for perturbation. Six genes with immunological relevance were differentially expressed in oil-fed mink. Interleukin-18 (IL-18), IL-10, inducible nitric oxide synthase (iNOS), cyclooxygenase 2 (COX-2), and complement cytolysis inhibitor (CLI) were down-regulated while IL-2 was up-regulated. Expression of two additional genes was affected; heat shock protein 70 (HSP70) was up-regulated and thyroid hormone receptor (THR) was down-regulated. While the significance of each perturbation is not immediately evident, we identified differential expression of genes that would be consistent with the presence of immune system-modifying and endocrine-disrupting compounds in fuel oil. Application of this approach to identify effects of petroleum contamination on sea otters should be possible following expansion of this mink model to identify a greater number of affected genes in peripheral blood leukocytes.

Variations of transcript profiles between sea otters Enhydra lutris from Prince William Sound, Alaska, and clinically normal reference otters

“…Interestingly, the gene AHR was not strongly differentially expressed in this nor the mink study (Bowen et al 2007). Up-regulation of AHR is indicative of immediate exposure to classes of environmental toxicants including polycyclic aromatic hydrocarbons, polyhalogenated hydrocarbons, dibenzofurans, and dioxin (Oesch-Bartlomowicz & Oesch 2005).…”

“…The genes selected in our study were based on a suite of genes transcribed in American mink (Neovison vison) experimentally exposed to crude oil (Bowen et al 2007). Although targeted for oil exposure, these genes represent immune function responses to potential biological, physical, or anthropogenic inputs, and can be sensitive indicators of environmental stressors, particularly those that cause subtle or chronic effects on an organism.…”

“…A change in gene transcription in peripheral blood leukocytes was evident in American mink Mustela vison exposed to petroleum oil (Bowen et al 2007). Sensitive and specific gene markers were developed using samples previously collected from mink with subtle petroleum oil-associated pathophysiological anomalies and altered lymphocyte function (Schwartz et al 2004a,b).…”

“…The effects of oil exposure, as with other toxins, could involve multiple organ systems and change with dose and route of exposure. Bowen et al (2007) identified genes in the mink that were significantly altered in transcription by exposure to oil. These genes play a role in immunomodulation, inflammation, cytoprotection, tu mor suppression, reproduction, cellular stressresponse, metal metabolism, xenobiotic metabolizing enzymes, antioxidant enzymes, and cell-cell adhesion (Bowen et al 2011).…”

“…Using these degenerate primers on sea otter complementary DNA (cDNA), we sequenced 10 target ge nes and 1 reference gene identified in the mink panel (Bowen et al 2006a(Bowen et al , 2007(Bowen et al , 2011. The objective of our study was to compare transcription of targeted genes in sea otters sampled in 2008 among areas within PWS that had been impacted to varying degrees by the EVOS with reference groups of sea otters diagnosed as 'clinically normal', consisting of captive aquarium animals sampled from 2008 to 2010, and free-ranging animals from the Alaska Peninsula sampled in 2009 from an area with no known, large-scale anthropogenic impacts (Bowen et al 2011).…”