title: RNA sequencing analysis of transcriptional change in the freshwater mussel Elliptio complanata after environmentally relevant sodium chloride exposure.
abstract: To identify potential biomarkers of salt stress in a freshwater sentinel species, we examined transcriptional responses of the common mussel Elliptio complanata to controlled sodium chloride (NaCl) exposures. Ribonucleic acid sequencing (RNA-Seq) of mantle tissue identified 481 transcripts differentially expressed in adult mussels exposed to 2 ppt NaCl (1.2 ppt chloride) for 7 d, of which 290 had nonoverlapping intervals. Differentially expressed gene categories included ion and transmembrane transport, oxidoreductase activity, maintenance of protein folding, and amino acid metabolism. The rate-limiting enzyme for synthesis of taurine, an amino acid frequently linked to osmotic stress in aquatic species, was upregulated, as was the transmembrane ion pump sodium/potassium adenosine 5'-triphosphatase. These patterns confirm a primary transcriptional response to the experimental dose, albeit likely overlapping with nonspecific secondary stress responses. Substantial involvement of the heat shock protein 70 chaperone family and the water-transporting aquaporin family was not detected, however, in contrast to some studies in other bivalves. A subset of the most significantly regulated genes was confirmed by quantitative polymerase chain reaction in an independent sample. Cluster analysis showed separation of mussels exposed to 2 ppt NaCl from control mussels in multivariate space, but mussels exposed to 1 ppt NaCl were largely indistinguishable from controls. Transcriptome-scale analysis of salt exposure under laboratory conditions efficiently identified candidate biomarkers for further functional analysis and field validation. Environ Toxicol Chem 2017;36:2352-2366. © Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America.
authors.affiliation: Leetown Science Center, US Geological Survey, Kearneysville, West Virginia.
authors.forename: Laura S
authors.initials: LS
authors.lastname: Robertson
authors.affiliation: Northern Appalachian Research Laboratory, Leetown Science Center, US Geological Survey, Wellsboro, Pennsylvania.
authors.forename: Heather S
authors.initials: HS
authors.lastname: Galbraith
authors.affiliation: Leetown Science Center, US Geological Survey, Kearneysville, West Virginia.
authors.forename: Deborah
authors.initials: D
authors.lastname: Iwanowicz
authors.affiliation: Northern Appalachian Research Laboratory, Leetown Science Center, US Geological Survey, Wellsboro, Pennsylvania.
authors.forename: Carrie J
authors.initials: CJ
authors.lastname: Blakeslee
authors.affiliation: Fort Collins Science Center, US Geological Survey, Fort Collins, Colorado.
authors.forename: R Scott
authors.initials: RS
authors.lastname: Cornman
mesh_terms: D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D004781:Environmental Exposure; D005618:Fresh Water / Q000737:chemistry; D009997:Osmotic Pressure; D054712:Salinity; D017423:Sequence Analysis, RNA; D012965:Sodium Chloride / Q000633:toxicity*; D000254:Sodium-Potassium-Exchanging ATPase / Q000235:genetics / Q000378:metabolism; D013312:Stress, Physiological; D013654:Taurine / Q000378:metabolism; D014158:Transcription, Genetic; D059467:Transcriptome; D049876:Unionidae / Q000187:drug effects* / Q000235:genetics / Q000378:metabolism
chemical_list: D015415:Biomarkers; D013654:Taurine; D012965:Sodium Chloride; D000254:Sodium-Potassium-Exchanging ATPase
keywords: Biomarker; Ecotoxicogenomics; Freshwater toxicology