Gene expression, glutathione status, and indicators of hepatic oxidative stress in laughing gull (Larus atricilla) hatchlings exposed to methylmercury.
Despite extensive studies of methylmercury (MeHg) toxicity in birds, molecular effects on birds are poorly characterized. To improve our understanding of toxicity pathways and identify novel indicators of avian exposure to Hg, the authors investigated genomic changes, glutathione status, and oxidative status indicators in liver from laughing gull (Larus atricilla) hatchlings that were exposed in ovo to MeHg (0.05-1.6 µg/g). Genes involved in the transsulfuration pathway, iron transport and storage, thyroid-hormone related processes, and cellular respiration were identified by suppression subtractive hybridization as differentially expressed. Quantitative polymerase chain reaction (qPCR) identified statistically significant effects of Hg on cytochrome C oxidase subunits I and II, transferrin, and methionine adenosyltransferase RNA expression. Glutathione-S-transferase activity and protein-bound sulfhydryl levels decreased, whereas glucose-6-phosphate dehydrogenase activity increased dose-dependently. Total sulfhydryl concentrations were significantly lower at 0.4 µg/g Hg than in controls. Together, these endpoints provided some evidence of compensatory effects, but little indication of oxidative damage at the tested doses, and suggest that sequestration of Hg through various pathways may be important for minimizing toxicity in laughing gulls. This is the first study to describe the genomic response of an avian species to Hg. Laughing gulls are among the less sensitive avian species with regard to Hg toxicity, and their ability to prevent hepatic oxidative stress may be important for surviving levels of MeHg exposures at which other species succumb.
USGS Patuxent Wildlife Research Center, Beltsville, MD, USA.
Kathryn
K
Jenko
Natalie K
NK
Karouna-Renier
David J
DJ
Hoffman
D000818:Animals; D046091:Charadriiformes / Q000378:metabolism*; D020387:Food Chain; D015870:Gene Expression / Q000187:drug effects; D005978:Glutathione / Q000378:metabolism*; D008099:Liver / Q000187:drug effects* / Q000378:metabolism / Q000503:physiopathology; D008767:Methylmercury Compounds / Q000633:toxicity*; D010063:Ovum / Q000187:drug effects; D018384:Oxidative Stress / Q000187:drug effects*; D012333:RNA, Messenger / Q000032:analysis; D013438:Sulfhydryl Compounds / Q000378:metabolism; D059467:Transcriptome
D008767:Methylmercury Compounds; D012333:RNA, Messenger; D013438:Sulfhydryl Compounds; D005978:Glutathione