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.

A weight‐of‐evidence approach for defining thermal sensitivity in a federally endangered species

“…New and reliable methods for quantifying stress in mussels could include the use of custom intermittent flow respirometry systems, which may provide improved means for quantifying respiration and clearance rates (Steffensen, ; Sui et al, ; Svendsen, Bushnell, & Steffensen, ). Alternatively, molecular markers have been developed for assessing physiological responses to stressors in other aquatic taxa (Denslow, Garcia‐Reyero, & Barber, ); however, few studies have applied this technology to freshwater mussels (but see Bertucci et al, ; Luo et al, ; Robertson, Galbraith, Iwanowicz, Blakeslee, & Cornman, ). Carefully selected molecular markers have the added benefit of providing insight into the mechanism (pathway) of the physiological response (Denslow et al, ).…”

“…Alternatively, molecular markers have been developed for assessing physiological responses to stressors in other aquatic taxa (Denslow, Garcia-Reyero, & Barber, 2007); however, few studies have applied this technology to freshwater mussels (but see Bertucci et al, 2017;Luo et al, 2014;Robertson, Galbraith, Iwanowicz, Blakeslee, & Cornman, 2017). Carefully selected molecular markers have the added benefit of providing insight into the mechanism (pathway) of the physiological response (Denslow et al, 2007).…”

Identifying conserved polychaete molecular markers of metal exposure: Comparative analyses using the Alitta virens (Annelida, Lophotrochozoa) transcriptome

“…We have taken a more conservative approach, limiting ourselves to identifying genes with pronounced differential expression patterns, where the cut-off for differential expressed genes is decided using qPCR. Similar approaches have provided reliable indications of pronounced gene expression differences (Al Seesi et al, 2014;Neave et al, 2012;Short et al, 2014;Wippler et al, 2016;Robertson et al, 2017). As we used qPCR to validate the RNASeq compar ison of control and exposed animals, it was important to identify reliable reference genes.…”

The Status of Mussel Health Assessment and a Path Forward

“…2017; Roznere et al 2017), and exposure to an estrogenic compound (Leonard et al 2014). Other recent studies evaluated mussel gene responses to stress using transcriptomes (Wang et al 2012;Cornman et al 2014;Luo et al 2014;Robertson et al 2017;Jeffrey et al 2018;Roznere et al 2018;Waller et al 2019).…”