Citation:

Reichman, J., J. Steevens, R. Hockett, A. Farag, D. Harper, H. Ren, A. Fisher, N. Kimble, D. Ekman, AND M. Jankowski. Transcriptome Responses of Rainbow Trout and Chinook Salmon to Sub-Lethal Exposures to Zinc. SETAC North America, 43rd Annual Meeting, Pittsburgh, PA, November 13 - 17, 2022.

Impact/Purpose:

Metals occur in surface waters naturally but may be elevated as a result of mining activities, roadway runoff and other sources. Aquatic life, including Federally Threatened and Endangered Species (T&E Species) may be exposed and experience ill effects. EPA regularly conducts ecological risk assessments to determine if its decisions incorporate an understanding of the sensitivity of T&E Species to metals exposure. However, because toxicity information will generally be limited for Listed species, new approaches are needed to help the agency use existing toxicity information for its assessments. Using advanced genomics tools and focusing on two salmonid species, the authors compared transcriptome changes in Rainbow trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus tshawytscha) exposed to zinc to determine the influence of taxonomic relatedness on molecular impacts from metal exposures across closely related taxa. The authors found that there were 22 impacted biochemical pathways shared between the species. Such knowledge indicates that the extrapolation of metals toxicity data across fish taxa during risk assessments focused on T&E Species has a defined biological basis. The project aims to enhance the scientific basis for ecological risk assessment work at EPA and beyond in order to more efficiently accomplish the mission to protect environmental health.

Description:

In the environment, fish are often exposed to cationic metals from mining activities, roadway runoff, and other sources. Data are needed on the influence of taxonomic relatedness regarding the molecular impacts from metal exposures among closely related taxa to help inform decisions on the potential use of surrogate species in toxicity risk assessments. Thus, we compared transcriptome changes in fin, gill, and liver of juvenile rainbow trout (Oncorhynchus mykiss) and Chinook salmon (Oncorhynchus tshawytscha) exposed to zinc (Zn) in control laboratory waters, and at 17%, or 50% of available 96-hour LC50 concentrations for 24 or 96 hours (N=6 per experimental group). Trimmed Illumina RNA-Seq reads from trout and salmon were aligned to GCF_002163495_1_Omyk_1.0_rna and GCF_018296145.1_Otsh_v2.0_rna templates respectively. Expression levels compared to controls were normalized with DESeq2 and differentially expressed genes (DEGs) were identified (i.e., ≥2-fold change, corrected P ≤0.05 and signal ≥10). Enrichment of KEGG and Reactome pathways by DEGs was tested by Fisher’s Exact Test (corrected FDR = 0.05). Rainbow trout had 1632 DEGs across all groups, while there were 10809 in Chinook salmon. For both species, the majority of DEGs came from gill tissue (58% and 96%, respectively).  There were 89 significantly enriched pathways for trout and 212 for salmon with 22 shared between the species. For both species there were proportional increases of impacted pathways associated with higher Zn concentration and longer exposure duration. The top hierarchical categories for the shared pathways were cell cycle, cellular responses to stimuli, environmental information processing, extracellular matrix organization, genetic information processing, hemostasis, immune system, metabolism, metabolism of RNA, organismal systems, and signal transduction. The results suggest that a diverse core of salmonid-specific transcriptome responses to Zn exposure is present within the broader changes seen in each species. Investigations are underway to identify the extent to which these pathways are also affected by Zn in more distantly related fish including zebrafish (Danio rerio) and medaka (Oryzias latipes). In addition, we are checking for relationships between salmonid transcriptome changes and metabolomic shifts.

Record Details: